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Can beavers control the direction a tree falls?

Can beavers control the direction a tree falls?


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We humans can easily control the direction a tree falls by making a number of strategic cuts, essentially creating a hinge:

This prevents trees from falling on equipment and people and sets them up in a good location for the subsequent processing steps. I'm curious if beavers also perform directional felling and, if they do, how do they choose the direction (eg to fell the tree towards the damn, in a river, away from thick brush, etc)?

In this picture (and others), it appears as though the beaver has created a hinge. Is their any method to their technique or do they just start chewing and hope for the best?


It is difficult to find a scientific answer to this question, but let me insert this citation from a specialist site:

Contrary to popular belief, beaver cannot plan the direction in which trees will fall. Many trees become hung up in the branches of surrounding trees and are lost to the colony. In heavily forested areas, this loss may amount to one-half of the trees felled.

Another source says the same.


But scientists think beavers may actually plan the direction of falling:

By measuring the falling angle of 888 trees of a variety of sizes cut near 8 different dams in southwestern Saskatchewan, we tested the hypothesis that beavers (Castor canadensis) fell trees in a non-random direction. We predicted that trees would be preferentially felled towards the dam to minimize the costs of transporting materials to the dam and to minimize the amount of time beavers spend on land. We established a 150 m wide × 250 m long transect at each dam and determined the felling angle of at least 100 aspen trees cut in each transect. We found that trees were felled by beavers with a mean felling angle of 357.9°, a direction not significantly different from that of the dam. In all, 62% of trees were felled within 45° of the direction of the dam. While our data are consistent with the hypothesis, an experimental test is required to establish the reason(s) for the pattern we found.

Their picture is better than thousands of words:

And another paper:

We studied patterns in the orientation of cutting when beavers (Castor canadensis) cut trees around Alum Creek Lake in central Ohio. For 462 trees, we measured the slope at the base of the tree, the orientation of the cut relative to this slope, the distance of the tree from the water, the radius of the tree, and the symmetry of the cut. The land around Alum Creek Lake generally slopes toward the water, so to direct the fall of a tree towards the water a beaver should cut a symmetrical tree from the downhill side. Cutting from the downhill side occurred for trees >9.0 m from the water. Near the shore, trees tended to lean toward the water and would fall toward the water regardless of the side from which the beaver cut. At distances <9-0 m from shore, beavers cut predominantly from the uphill side where it should be easy to sit and there is little danger of the tree falling on them. At all distances, beavers showed random orientation when cutting trees on shallow slopes (<20°), whereas on steep slopes (especially slopes >30°) they cut predominantly from the uphill side. Beavers cut small trees (<5.0 cm diameter) mostly from the downhill side, but tended to cut trees >5.0 cm in diameter from the uphill side. Overall, enough factors interacted that no single pattern of cutting existed for all trees.


How to Fell a Tree

This article was co-authored by Mike Garcia. Mike Garcia is a Licensed Landscape Contractor and the Founder of Enviroscape LA, a full-service landscape design and construction firm in Los Angeles, California. With over 30 years of experience, Mike specializes in sustainable landscape practices. Mike holds an Ornamental Horticulture degree, C-27 Landscape Contractor and D-49 Tree Service Contractor licenses, and Permaculture Design, California Naturalist, International Certified Professional Pond Contractor, and Pond Building certifications. He is one of eight Internationally Certified Pond Builders in the world. Enviroscape LA has won landscape and water feature awards from the International Professional Pond Contractors Association (IPPCA), National Association of Pond Professionals (NAPP), and the California Landscape Contractors Association (CLCA). Mike is a past president of the CLCA and currently serves on their local Board of Directors. Enviroscape LA has been featured in PONDS USA Magazine, Pond and Garden Lifestyles Magazine, and the Los Angeles Times. Mike has appeared on Extreme Home Makeover, HGTV's Landscapers Challenge, and A & E's series Fix That Yard.

There are 14 references cited in this article, which can be found at the bottom of the page.

wikiHow marks an article as reader-approved once it receives enough positive feedback. In this case, 100% of readers who voted found the article helpful, earning it our reader-approved status.

This article has been viewed 635,324 times.

If you want to cut down a tree, it's important that you use the right techniques and follow safety precautions because it's potentially dangerous. [1] X Expert Source

Mike Garcia
Licensed Landscape Contractor Expert Interview. 20 November 2020. To fell a tree, you should scout out the tree and the area around the tree to make sure that it has a safe path to fall. Then, you'll need to create a notch in the side of the tree with a chainsaw or hatchet so that you can control how it falls. If you follow the right steps, you can safely cut down a tree.


Scientific Classification

Kingdom Plantae
Phylum Pinophyta
Class Pinopsida
Order Pinales
Family Pinaceae
Genus Pinus
Subgenus Strobus
Species Pinus Strobus


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Contents

Philosophy in classical Greece is the ultimate origin of the Western conception of the nature of things. [12]

According to Aristotle, the philosophical study of human nature itself originated with Socrates, who turned philosophy from study of the heavens to study of the human things. [16] Though leaving no written works, Socrates is said to have studied the question of how a person should best live. It is clear from the works of his students, Plato and Xenophon, and also from the accounts of Aristotle (Plato's student), that Socrates was a rationalist and believed that the best life and the life most suited to human nature involved reasoning. The Socratic school was the dominant surviving influence in philosophical discussion in the Middle Ages, amongst Islamic, Christian, and Jewish philosophers.

The human soul in the works of Plato and Aristotle has a nature that is divided in a specifically human way. One part is specifically human and rational, being further divided into (1) a part which is rational on its own and (2) a spirited part which can understand reason. Other parts of the soul are home to desires or passions similar to those found in animals. In both Aristotle and Plato, spiritedness (thumos) is distinguished from the other passions (epithūmíā). [17] The proper function of the "rational" was to rule the other parts of the soul, helped by spiritedness. By this account, using one's reason is the best way to live, and philosophers are the highest types of humans.

Aristotle Edit

Aristotle—Plato's most famous student-made some of the most famous and influential statements about human nature. In his works, apart from using a similar scheme of a divided human soul, some clear statements about human nature are made:

  • Man is a conjugal animal: An animal that is born to couple in adulthood. In doing so, man builds a household (oikos) and, in more successful cases, a clan or small village still run upon patriarchal lines. [18]
  • Man is a political animal: An animal with an innate propensity to develop more complex communities (i.e. the size of a city or town), with systems of law-making and a division of labor. This type of community is different in kind from a large family, and requires the special use of human reason. [19]
  • Man is a mimetic animal: Man loves to use his imagination, and not only to make laws and run town councils: "[W]e enjoy looking at accurate likenesses of things which are themselves painful to see, obscene beasts, for instance, and corpses.… [The] reason why we enjoy seeing likenesses is that, as we look, we learn and infer what each is, for instance, 'that is so and so. ' " [20]

For Aristotle, reason is not only what is most special about humanity compared to other animals, but it is also what we were meant to achieve at our best. Much of Aristotle's description of human nature is still influential today. However, the particular teleological idea that humans are "meant" or intended to be something has become much less popular in modern times. [21]

Theory of four causes Edit

For the Socratics, human nature, and all natures, are metaphysical concepts. Aristotle developed the standard presentation of this approach with his theory of four causes, whereby every living thing exhibits four aspects, or "causes:"

For example, an oak tree is made of plant cells (matter) grows from an acorn (effect) exhibits the nature of oak trees (form) and grows into a fully mature oak tree (end). According to Aristotle, human nature is an example of a formal cause. Likewise, our 'end' is to become a fully actualized human being (including fully actualizing the mind). Aristotle suggests that the human intellect ( νοῦς , noûs), while "smallest in bulk", is the most significant part of the human psyche and should be cultivated above all else. [22] The cultivation of learning and intellectual growth of the philosopher is thereby also the happiest and least painful life.

Confucianism Edit

Human nature is a central question in Chinese philosophy. [23] From the Song dynasty, the theory of potential or innate goodness of human beings became dominant in Confucianism. [24]

Mencius Edit

Mencius argues that human nature is good, [23] [25] understanding human nature as the innate tendency to an ideal state that's expected to be formed under the right conditions. [26] Therefore, humans have the capacity to be good, even though they are not all good. [26]

According to Mencian theory, human nature contains four beginnings ( 端 duan ) of morality: [27]

  1. a sense of compassion that develops into benevolence ( 仁 ren )
  2. a sense of shame and disdain that develops into righteousness ( 義 yi )
  3. a sense of respect and courtesy that develops into propriety ( 禮 li ) and
  4. a sense of right and wrong that develops into wisdom ( 智 zhi ). [25][27]

The beginnings of morality are characterized by both affective motivations and intuitive judgments, such as what's right and wrong, deferential, respectful, or disdainful. [27]

In Mencius' view, goodness is the result of the development of innate tendencies toward the virtues of benevolence, righteousness, wisdom, and propriety. [25] The tendencies are manifested in moral emotions for every human being. [25] Reflection ( 思 si ) upon the manifestations of the four beginnings leads to the development of virtues. [25] It brings recognition that virtue takes precedence over satisfaction, but a lack of reflection inhibits moral development. [27] In other words, humans have a constitution comprising emotional predispositions that direct them to goodness. [25]

Mencius also addresses the question why the capacity for evil is not grounded in human nature. [25] If an individual becomes bad, it is not the result of his or her constitution, as their constitution contains the emotional predispositions that direct to goodness, but a matter of injuring or not fully developing his or her constitution in the appropriate direction. [25] He recognizes desires of the senses as natural predispositions distinct from the four beginnings. [27] People can be misled and led astray by their desires if they do not engage their ethical motivations. [25] He therefore places responsibility on people to reflect on the manifestations of the four beginnings. [27] Herein, it is not the function of ears and eyes but the function of the heart to reflect, as sensory organs are associated with sensual desires but the heart is the seat of feeling and thinking. [28] Mencius considers core virtues—benevolence, righteousness, propriety, and wisdom—as internal qualities that humans originally possess, so people can not attain full satisfaction by solely pursuits of self-interest due to their innate morality. [29] Wong (2018) underscores that Mencius' characterization of human nature as good means that "it contains predispositions to feel and act in morally appropriate ways and to make intuitive normative judgments that can with the right nurturing conditions give human beings guidance as to the proper emphasis to be given to the desires of the senses." [27]

Mencius sees ritual (i.e., the standard for how humans should treat and interact with each other) as an outward expression of the inherent moral sense in human nature. [29]

Xunzi Edit

Mencius' view of ritual is in contrast to Xunzi, who does not view moral sense as an innate part of human nature. [30] Rather, a moral sense is acquired through learning, in which one engages in and reflects upon a set of ritual practices. [30] Xunzi's claim that human nature is bad, according to Ivanhoe (1994), means that humans do not have a conception of morality and therefore must acquire it through learning, lest destructive and alienating competition inevitably arises from human desire. [30]

Xunzi understands human nature as the basic faculties, capacities, and desires that people have from birth. [26] He argues that human nature is evil and that any goodness is the result of human activity. [23] [31] It is human nature to seek profit, because humans desire for sensory satisfaction. [31] Xunzi states that "Now the nature of man is evil. It must depend on teachers and laws to become correct and achieve propriety and righteousness and then it becomes disciplined." [23] He underscores that goodness comes from the traits and habits acquired through conscious actions, which he calls artifice ( 偽 wei ). [26] Therefore, morality is seen as a human artifice but not as a part of human nature. [32]

Legalism Edit

Human nature is one of the major pillars of Legalism in China. [33] However, Legalists do not concern themselves with whether human goodness or badness is inborn, and whether human beings possess the fundamental qualities associated with that nature. [33]

Legalists see the overwhelming majority of human beings as selfish in nature. [33] They hold the view that human nature is evil, in which individuals are driven by selfishness. [34] Therefore, people are not expected to always behave morally. [33] For instance, due to the corrupt nature of humans, Legalists did not trust that officials would carry out their duties in a fair and impartial manner. [35] There is a perpetual political struggle, characterized by conflict among contending human actors and interests, where individuals are easily tempted due to their selfish nature at the expense of others. [34]

According to Legalism, selfishness in human nature can not be eliminated or altered by education or self-cultivation. [33] [36] It dismisses the possibility that people can overcome their selfishness and considers the possibility that people can be driven by moral commitment to be exceptionally rare. [33] Legalists do not see the individual morality of both the rulers or the ruled as an important concern in a political system. [33] Instead, Legalist thinkers such as Han Fei emphasize clear and impersonal norms and standards (such as laws, regulations, and rules) as the basis to maintain order. [33]

As human nature has an unchanging selfish but satiable core, Han Fei argues that competition for external goods during times of scarcity produces disorder, while times of abundance simply mean that people do not fall back into chaos and conflict but not that they are necessarily nice. [36] Additionally, Han Fei argues that people are all motivated by their unchanging selfish core to want whatever advantage they can gain from whomever they can gain such advantage, which especially comes to expression in situations where people can act with impunity. [36]

Legalists posit that human selfishness can be an asset rather than a threat to a state. [33] It is axiomatic in Legalism that the government can not be staffed by upright and trustworthy men of service, because every member of the elite—like any member of society—will pursue their own interests and thus must be employed for their interests. [33] Herein, individuals must be allowed to pursue their selfish interests exclusively in a manner that benefits rather than contradicts the needs of a state. [33] Therefore, a political system that presupposes this human selfishness is the only viable system. [33] In contrast, a political system based on trust and respect (rather than impersonal norms and standards) brings great concern with regard to an ongoing and irresolvable power struggle. [33] Rather, checks and controls must be in place to limit the subversion of the system by its actors (such as ministers and other officials). [33] Legalists view the usage of reward and punishment as effective political controls, as it is in human nature to have likes and dislikes. [34] For instance, according to the Legalist statesman Shang Yang, it is crucial to investigate the disposition of people in terms of rewards and penalties when a law is established. [33] He explains that a populace can not be driven to pursuits of agriculture or warfare if people consider these to be bitter or dangerous on the basis of calculations about their possible benefits, but people can be directed toward these pursuits through the application of positive and negative incentives. [33] As an implication of the selfish core in human nature, Han Fei remarks that "Those who act as ministers fear the penalties and hope to profit by the rewards." [36]

In Han Fei's view, the only realistic option is a political system that produces equivalents of junzi (君子, who are virtuous exemplars in Confucianism) but not junzi. [36] This does not mean, however, that Han Fei makes a distinction between seeming and being good, as he does not entertain the idea that humans are good. [36] Rather, as human nature is constituted by self-interest, he argues that humans can be shaped behaviorally to yield social order if it is in the individual's own self-interest to abide by the norms (i.e., different interests are aligned to each other and the social good), which is most efficiently ensured if the norms are publicly and impartially enforced. [36]

In Christian theology, there are two ways of "conceiving human nature:" The first is "spiritual, Biblical, and theistic" and the second is "natural, cosmical, and anti-theistic". [37] : 6 The focus in this section is on the former. As William James put it in his study of human nature from a religious perspective, "religion" has a "department of human nature". [38]

Various views of human nature have been held by theologians. However, there are some "basic assertions" in all "biblical anthropology:" [39]

  1. "Humankind has its origin in God, its creator."
  2. "Humans bear the 'image of God'."
  3. Humans are "to rule the rest of creation".

The Bible contains no single "doctrine of human nature". Rather, it provides material for more philosophical descriptions of human nature. [40] For example, Creation as found in the Book of Genesis provides a theory on human nature. [41]

Catechism of the Catholic Church, under the chapter "Dignity of the human person", provides an article about man as image of God, vocation to beatitude, freedom, human acts, passions, moral conscience, virtues, and sin. [42]

Created human nature Edit

As originally created, the Bible describes "two elements" in human nature: "the body and the breath or spirit of life breathed into it by God". By this was created a "living soul", meaning a "living person". [43] According to Genesis 1:27, this living person was made in the "image of God". [44] From the biblical perspective, "to be human is to bear the image of God." [45] : 18

Genesis does not elaborate the meaning of "the image of God", but scholars find suggestions. One is that being created in the image of God distinguishes human nature from that of the beasts. [46] Another is that as God is "able to make decisions and rule" so humans made in God's image are "able to make decisions and rule". A third is that mankind possesses an inherent ability "to set goals" and move toward them. [45] : 5, 14 That God denoted creation as "good" suggests that Adam was "created in the image of God, in righteousness". [47]

Adam was created with ability to make "right choices", but also with the ability to choose sin, by which he fell from righteousness into a state of "sin and depravity". [45] : 231 Thus, according to the Bible, "humankind is not as God created it." [48]

Fallen human nature Edit

By Adam's fall into sin, "human nature" became "corrupt", although it retains the image of God. Both the Old Testament and the New Testament teach that "sin is universal." [45] : 17, 141 For example, Psalm 51:5 reads: "For behold I was conceived in iniquities and in sins did my mother conceive me." [49] Jesus taught that everyone is a "sinner naturally" because it is mankind's "nature and disposition to sin". [37] : 124–5 Paul, in Romans 7:18, speaks of his "sinful nature". [50]

Such a "recognition that there is something wrong with the moral nature of man is found in all religions." [45] : 141 Augustine of Hippo coined a term for the assessment that all humans are born sinful: original sin. [51] Original sin is "the tendency to sin innate in all human beings". [52] The doctrine of original sin is held by the Catholic Church and most mainstream Protestant denominations, but rejected by the Eastern Orthodox Church, which holds the similar doctrine of ancestral fault.

"The corruption of original sin extends to every aspect of human nature": to "reason and will" as well as to "appetites and impulses". This condition is sometimes called "total depravity". [53] Total depravity does not mean that humanity is as "thoroughly depraved" as it could become. [54] Commenting on Romans 2:14, John Calvin writes that all people have "some notions of justice and rectitude . which are implanted by nature" all people. [55]

Adam embodied the "whole of human nature" so when Adam sinned "all of human nature sinned." [56] The Old Testament does not explicitly link the "corruption of human nature" to Adam's sin. However, the "universality of sin" implies a link to Adam. In the New Testament, Paul concurs with the "universality of sin". He also makes explicit what the Old Testament implied: the link between humanity's "sinful nature" and Adam's sin [57] In Romans 5:19, Paul writes, "through [Adam's] disobedience humanity became sinful." [58] Paul also applied humanity's sinful nature to himself: "there is nothing good in my sinful nature." [59] [60]

The theological "doctrine of original sin" as an inherent element of human nature is not based only on the Bible. It is in part a "generalization from obvious facts" open to empirical observation. [61]

Empirical view Edit

A number of experts on human nature have described the manifestations of original (i.e., the innate tendency to) sin as empirical facts.

  • Biologist Richard Dawkins, in his The Selfish Gene, states that "a predominant quality" in a successful surviving gene is "ruthless selfishness". Furthermore, "this gene selfishness will usually give rise to selfishness in individual behavior." [62]
  • Child psychologist Burton L. White finds a "selfish" trait in children from birth, a trait that expresses itself in actions that are "blatantly selfish". [63][64]
  • Sociologist William Graham Sumner finds it a fact that "everywhere one meets "fraud, corruption, ignorance, selfishness, and all the other vices of human nature". [65] He enumerates "the vices and passions of human nature" as "cupidity, lust, vindictiveness, ambition, and vanity". Sumner finds such human nature to be universal: in all people, in all places, and in all stations in society. [66]
  • Psychiatrist Thomas Anthony Harris, on the basis of his "data at hand", observes "sin, or badness, or evil, or 'human nature', whatever we call the flaw in our species, is apparent in every person." Harris calls this condition "intrinsic badness" or "original sin". [67]

Empirical discussion questioning the genetic exclusivity of such an intrinsic badness proposition is presented by researchers Elliott Sober and David Sloan Wilson. In their book, Unto Others: The Evolution and Psychology of Unselfish Behavior, they propose a theory of multilevel group selection in support of an inherent genetic "altruism" in opposition to the original sin exclusivity for human nature. [68]

20th century Liberal Theology Edit

Liberal theologians in the early 20th century described human nature as "basically good", needing only "proper training and education". But the above examples document the return to a "more realistic view" of human nature "as basically sinful and self-centered". Human nature needs "to be regenerated . to be able to live the unselfish life". [69]

Regenerated human nature Edit

According to the Bible, "Adam's disobedience corrupted human nature" but God mercifully "regenerates". [70] "Regeneration is a radical change" that involves a "renewal of our [human] nature". [71] Thus, to counter original sin, Christianity purposes "a complete transformation of individuals" by Christ. [72]

The goal of Christ's coming is that fallen humanity might be "conformed to or transformed into the image of Christ who is the perfect image of God", as in 2 Corinthians 4:4. [73] The New Testament makes clear the "universal need" for regeneration. [74] A sampling of biblical portrayals of regenerating human nature and the behavioral results follow.

  • being "transformed by the renewing of your minds" (Romans 12:2) [75]
  • being transformed from one's "old self" (or "old man") into a "new self" (or "new man") (Colossians 3:9-10) [76]
  • being transformed from people who "hate others" and "are hard to get along with" and who are "jealous, angry, and selfish" to people who are "loving, happy, peaceful, patient, kind, good, faithful, gentle, and self-controlled" (Galatians 5:20-23) [77]
  • being transformed from looking "to your own interests" to looking "to the interests of others" (Philippians 2:4) [78]

One of the defining changes that occurred at the end of the Middle Ages was the end of the dominance of Aristotelian philosophy, and its replacement by a new approach to the study of nature, including human nature. [ citation needed ] In this approach, all attempts at conjecture about formal and final causes were rejected as useless speculation. [ citation needed ] Also, the term "law of nature" now applied to any regular and predictable pattern in nature, not literally a law made by a divine lawmaker, and, in the same way, "human nature" became not a special metaphysical cause, but simply whatever can be said to be typical tendencies of humans. [ citation needed ]

Although this new realism applied to the study of human life from the beginning—for example, in Machiavelli's works—the definitive argument for the final rejection of Aristotle was associated especially with Francis Bacon. Bacon sometimes wrote as if he accepted the traditional four causes ("It is a correct position that "true knowledge is knowledge by causes." And causes again are not improperly distributed into four kinds: the material, the formal, the efficient, and the final") but he adapted these terms and rejected one of the three:

But of these the final cause rather corrupts than advances the sciences, except such as have to do with human action. The discovery of the formal is despaired of. The efficient and the material (as they are investigated and received, that is, as remote causes, without reference to the latent process leading to the form) are but slight and superficial, and contribute little, if anything, to true and active science. [79]

This line of thinking continued with René Descartes, whose new approach returned philosophy or science to its pre-Socratic focus upon non-human things. Thomas Hobbes, then Giambattista Vico, and David Hume all claimed to be the first to properly use a modern Baconian scientific approach to human things.

Hobbes famously followed Descartes in describing humanity as matter in motion, just like machines. He also very influentially described man's natural state (without science and artifice) as one where life would be "solitary, poor, nasty, brutish and short". [80] Following him, John Locke's philosophy of empiricism also saw human nature as a tabula rasa. In this view, the mind is at birth a "blank slate" without rules, so data are added, and rules for processing them are formed solely by our sensory experiences. [81]

Jean-Jacques Rousseau pushed the approach of Hobbes to an extreme and criticized it at the same time. He was a contemporary and acquaintance of Hume, writing before the French Revolution and long before Darwin and Freud. He shocked Western civilization with his Second Discourse by proposing that humans had once been solitary animals, without reason or language or communities, and had developed these things due to accidents of pre-history. (This proposal was also less famously made by Giambattista Vico.) In other words, Rousseau argued that human nature was not only not fixed, but not even approximately fixed compared to what had been assumed before him. Humans are political, and rational, and have language now, but originally they had none of these things. [82] This in turn implied that living under the management of human reason might not be a happy way to live at all, and perhaps there is no ideal way to live. Rousseau is also unusual in the extent to which he took the approach of Hobbes, asserting that primitive humans were not even naturally social. A civilized human is therefore not only imbalanced and unhappy because of the mismatch between civilized life and human nature, but unlike Hobbes, Rousseau also became well known for the suggestion that primitive humans had been happier, "noble savages". [83]

Rousseau's conception of human nature has been seen as the origin of many intellectual and political developments of the 19th and 20th centuries. [84] He was an important influence upon Kant, Hegel, and Marx, and the development of German idealism, historicism, and romanticism.

What human nature did entail, according to Rousseau and the other modernists of the 17th and 18th centuries, were animal-like passions that led humanity to develop language and reasoning, and more complex communities (or communities of any kind, according to Rousseau).

In contrast to Rousseau, David Hume was a critic of the oversimplifying and systematic approach of Hobbes, Rousseau, and some others whereby, for example, all human nature is assumed to be driven by variations of selfishness. Influenced by Hutcheson and Shaftesbury, he argued against oversimplification. On the one hand, he accepted that, for many political and economic subjects, people could be assumed to be driven by such simple selfishness, and he also wrote of some of the more social aspects of "human nature" as something which could be destroyed, for example if people did not associate in just societies. On the other hand, he rejected what he called the "paradox of the sceptics", saying that no politician could have invented words like " 'honourable' and 'shameful,' 'lovely' and 'odious,' 'noble' and 'despicable ' ", unless there was not some natural "original constitution of the mind". [85]

Hume—like Rousseau—was controversial in his own time for his modernist approach, following the example of Bacon and Hobbes, of avoiding consideration of metaphysical explanations for any type of cause and effect. He was accused of being an atheist. He wrote:

We needn't push our researches so far as to ask "Why do we have humanity, i.e. a fellow-feeling with others?" It's enough that we experience this as a force in human nature. Our examination of causes must stop somewhere. [85]

After Rousseau and Hume, the nature of philosophy and science changed, branching into different disciplines and approaches, and the study of human nature changed accordingly. Rousseau's proposal that human nature is malleable became a major influence upon international revolutionary movements of various kinds, while Hume's approach has been more typical in Anglo-Saxon countries, including the United States. [ citation needed ]

According to Edouard Machery, the concept of human nature is an outgrowth of folk biology and in particular, the concept of folk essentialism - the tendency of ordinary people to ascribe essences to kinds. Machery argues that while the idea that humans have an "essence" is a very old idea, the idea that all humans have a unified human nature is relatively modern for a long time, people thought of humans as "us versus them" and thus did not think of human beings as a unified kind. [86]

The concept of human nature is a source of ongoing debate in contemporary philosophy, specifically within philosophy of biology, a subfield of the philosophy of science. Prominent critics of the concept – David L. Hull, [87] Michael Ghiselin, [88] and David Buller [89] see also [5] [6] [7] – argue that human nature is incompatible with modern evolutionary biology. Conversely, defenders of the concept argue that when defined in certain ways, human nature is both scientifically respectable and meaningful. [5] [6] [7] [90] [91] [92] Therefore, the value and usefulness of the concept depends essentially on how one construes it. This section summarizes the prominent construals of human nature and outlines the key arguments from philosophers on both sides of the debate.

Criticism of the concept of human nature (Hull) Edit

Philosopher of science David L. Hull has influentially argued that there is no such thing as human nature. Hull's criticism is raised against philosophers who conceive human nature as a set of intrinsic phenotypic traits (or characters) that are universal among humans, unique to humans, and definitive of what it is to be a member of the biological species Homo sapiens. In particular, Hull argues that such "essential sameness of human beings" is "temporary, contingent and relatively rare" in biology. [87] He argues that variation, insofar as it is the result of evolution, is an essential feature of all biological species. Moreover, the type of variation which characterizes a certain species in a certain historical moment is "to a large extent accidental" [87] He writes: [87] : 3

Periodically a biological species might be characterized by one or more characters which are both universally distributed among and limited to the organisms belonging to that species, but such states of affairs are temporary, contingent and relatively rare.

Hull reasons that properties universally shared by all members of a certain species are usually also possessed by members of other species, whereas properties exclusively possessed by the members of a certain species are rarely possessed by all members of that species. For these reasons, Hull observes that, in contemporary evolutionary taxonomy, belonging to a particular species does not depend on the possession of any specific intrinsic properties. Rather, it depends on standing in the right kind of relations (relations of genealogy or interbreeding, depending on the precise species concept being used) to other members of the species. Consequently, there can be no intrinsic properties that define what it is to be a member of the species Homo sapiens. Individual organisms, including humans, are part of a species by virtue of their relations with other members of the same species, not shared intrinsic properties.

According to Hull, the moral significance of his argument lies in its impact on the biologically legitimate basis for the concept of "human rights". While it has long been argued that there is a sound basis for "human rights" in the idea that all human beings are essentially the same, should Hull's criticism work, such a basis – at least on a biological level – would disappear. Nevertheless, Hull does not perceive this to be a fundamental for human rights, because people can choose to continue respecting human rights even without sharing the same human nature. [87]

Defences of the concept of human nature Edit

Several contemporary philosophers have attempted to defend the notion of human nature against charges that it is incompatible with modern evolutionary biology by proposing alternative interpretations. They claim that the concept of human nature continues to bear relevance in the fields of neuroscience and biology. Many have proposed non-essentialist notions. Others have argued that, even if Darwinism has shown that any attempt to base species membership on "intrinsic essential properties" is untenable, essences can still be "relational" – this would be consistent with the interbreeding, ecological, and phylogenetic species concepts, which are accepted by modern evolutionary biology. [93] These attempts aim to make Darwinism compatible with a certain conception of human nature which is stable across time.

"Nomological" account (Machery) Edit

Philosopher of science Edouard Machery has proposed that the above criticisms only apply to a specific definition (or "notion") of human nature, and not to "human nature in general". [91] He distinguishes between two different notions:

  • An essentialist notion of human nature - "Human nature is the set of properties that are separately necessary and jointly sufficient for being a human." These properties are also usually considered as distinctive of human beings. They are also intrinsic to humans and inherent to their essence. [91]
  • A nomological notion of human nature - "Human nature is the set of properties that humans tend to possess as a result of the evolution of their species." [91]

Machery clarifies that, to count as being "a result of evolution", a property must have an ultimate explanation in Ernst Mayr's sense. It must be possible to explain the trait as the product of evolutionary processes. Importantly, properties can count as part of human nature in the nomological sense even if they are not universal among humans and not unique to humans. In other words, nomological properties need not be necessary nor sufficient for being human. Instead, it is enough that these properties are shared by most humans, as a result of the evolution of their species – they "need to be typical". [94] Therefore, human nature in the nomological sense does not define what it is to be a member of the species Homo sapiens. Examples of properties that count as parts of human nature on the nomological definition include: being bipedal, having the capacity to speak, having a tendency towards biparental investment in children, having fear reactions to unexpected noises. [91] Finally, since they are the product of evolution, properties belonging to the nomological notion of human nature are not fixed, but they can change over time. [94]

Machery agrees with biologists and others philosophers of biology that the essentialist notion of human nature is incompatible with modern evolutionary biology: we cannot explain membership in the human species by means of a definition or a set of properties. However, he maintains that this does not mean humans have no nature, because we can accept the nomological notion which is not a definitional notion. Therefore, we should think of human nature as the many properties humans have in common as a result of evolution. [91]

Machery argues that notions of human nature can help explain why that, while cultures are very diverse, there are also many constants across cultures. For Machery, most forms of cultural diversity are in fact diversity on a common theme for example, Machery observes that the concept of a kinship system is common across cultures but the exact form it takes and the specifics vary between cultures. [95]

Problems with the nomological account Edit

Machery also highlights potential drawbacks of the nomological account. [91] One is that the nomological notion is a watered-down notion that cannot perform many of the roles that the concept of human nature is expected to perform in science and philosophy. The properties endowed upon humans by the nomological account do not distinguish humans from other animals or define what it is to be human. Machery pre-empts this objection by claiming that the nomological concept of human nature still fulfils many roles. He highlights the importance of a conception which picks out what humans share in common which can be used to make scientific, psychological generalizations about human-beings. [94] One advantage of such a conception is that it gives an idea of the traits displayed by the majority of human beings which can be explained in evolutionary terms.

Another potential drawback is that the nomological account of human nature threatens to lead to the absurd conclusion that all properties of humans are parts of human nature. According to the nomological account, a trait is only part of human nature if it is a result of evolution. However, there is a sense in which all human traits are results of evolution. For example, the belief that water is wet is shared by all humans. However, this belief is only possible because we have, for example, evolved a sense of touch. It is difficult to separate traits which are the result of evolution and those which are not. Machery claims the distinction between proximate and ultimate explanation can do the work here: only some human traits can be given an ultimate explanation, he argues.

According to the philosopher Richard Samuels [92] the account of human nature is expected to fulfill the five following roles:

  • an organizing function that demarks a territory of scientific inquiry
  • a descriptive function that is traditionally understood as specifying properties that are universal across and unique to human being
  • a causal explanatory function that offers causal explanation for occurring human behaviours and features
  • a taxonomic function that specifies possessing human nature as a necessary and sufficient criterion for belonging to the human species
  • Invariances that assume the understanding that human nature is to some degree fixed, invariable or at least hard to change and stable across time.

Samuels objects that Machery's nomological account fails to deliver on the causal explanatory function, because it claims that superficial and co-varying properties are the essence of human nature. Thus, human nature cannot be the underlying cause of these properties and accordingly cannot fulfill its causal explanatory role.

Philosopher Grant Ramsey also rejects Machery's nomological account. For him, defining human nature with respect to only universal traits fails to capture many important human characteristics. [90] Ramsey quotes the anthropologist Clifford Geertz, who claims that "the notion that unless a cultural phenomenon is empirically universal it cannot reflect anything about the nature of man is about as logical as the notion that because sickle-cell anemia is, fortunately, not universal, it cannot tell us anything about human genetic processes. It is not whether phenomena are empirically common that is critical in science. but whether they can be made to reveal the enduring natural processes that underly them." [96] Following Geertz, Ramsey holds that the study of human nature should not rely exclusively on universal or near-universal traits. There are many idiosyncratic and particular traits of scientific interest. Machery's account of human nature cannot give an account to such differences between men and women as the nomological account only picks out the common features within a species. In this light, the female menstrual cycle which is a biologically an essential and useful feature cannot be included in a nomological account of human nature. [90]

Ramsey [90] also objects that Machery uncritically adopts the innate-acquired dichotomy, distinguishing between human properties due to enculturation and those due to evolution. Ramsey objects that human properties do not just fall in one of the two categories, writing that "any organismic property is going to be due to both heritable features of the organism as well as the particular environmental features the organism happens to encounter during its life." [90]

"Causal essentialist" account (Samuels) Edit

Richard Samuels, in an article titled "Science and Human Nature", proposes a causal essentialist view that "human nature should be identified with a suite of mechanisms, processes, and structures that causally explain many of the more superficial properties and regularities reliably associated with humanity." [92] This view is "causal" because the mechanisms causally explain the superficial properties reliably associated with humanity by referencing the underlying causal structures the properties belong to. For example, it is true that the belief that water is wet is shared by all humans yet it is not in itself a significant aspect of human nature. Instead, the psychological process that lead us to assign the word "wetness" to water is a universal trait shared by all human beings. In this respect, the superficial belief that water is wet reveals an important causal psychological process which is widely shared by most human beings. The explanation is also "essentialist" because there is a core set of empirically discoverable cognitive mechanism that count as part of the human nature. According to Samuels, his view avoids the standard biological objections to human nature essentialism.

Samuels argues that the theoretical roles of human nature includes: organizing role, descriptive functions, causal explanatory functions, taxonomic functions, and invariances.

In comparison with traditional essentialist view, the "causal essentialist" view does not accomplish the taxonomic role of human nature (the role of defining what it is to be human). He claims however, that no conception could achieve this, as the fulfillment of the role would not survive evolutionary biologists’ objections (articulated above by in "Criticisms of the concept of human nature"). In comparison with Machery's nomological conception, Samuels wants to restore the causal-explanatory function of human nature. He defines the essence of human nature as causal mechanisms and not as surface-level properties. For instance, on this view, linguistic behaviour is not part of human nature, but the cognitive mechanisms underpinning linguistic behaviour might count as part of human nature.

"Life-history trait cluster" account (Ramsey) Edit

Grant Ramsey proposes an alternative account of human nature, which he names the "life-history trait cluster" account. [90] This view stems from the recognition that the combination of a specific genetic constitution with a specific environment is not sufficient to determine how a life will go, i.e., whether one is rich, poor, dies old, dies young, etc. Many ‘life histories’ are possible for a given individual, each populated by a great number of traits. Ramsey defines his conception of human nature in reference to the “pattern of trait clusters within the totality of extant possible life-histories”. [90] In other words, there are certain life histories, i.e., possible routes one's life can take, for example: being rich, being a PhD student, or getting ill. Ramsey underlines the patterns behind these possible routes by delving into the causes of these life histories. For example, one can make the following claim: “Humans sweat when they get exhausted" or one can also propose neurological claims such as “Humans secrete Adrenaline when they are in flight-fight mode.” This approach enables Ramsey to go beyond the superficial appearances and understand the similarities/differences between individuals in a deeper level which refers to the causal mechanisms (processes, structures and constraints etc.) which lie beneath them. Once we list all the possible life-histories of an individual, we can find these causal patterns and add them together to form the basis of individual nature.

Ramsey's next argumentative manoeuvre is to point out that traits are not randomly scattered across potential life histories there are patterns. “These patterns” he states “provide the basis for the notion of individual and human nature”. [90] : 987 While one's ‘individual nature’ consists of the pattern of trait clusters distributed across that individual's set of possible life histories, Human Nature, Ramsey defines as “the pattern of trait clusters within the totality of extant human possible life histories”. [90] : 987 Thus, if we were to combine all possible life histories of all individuals in existence we would have access to the trait distribution patterns that constitute human nature.

Trait patterns, on Ramsey's account, can be captured in the form of conditional statements, such as "if female, you develop ovaries" or "if male, you develop testes." These statements will not be true of all humans. Ramsey contends that these statements capture part of human nature if they have a good balance of pervasiveness (many people satisfy the antecedent of the conditional statement), and robustness (many people who satisfy the antecedent go on to satisfy the consequent).

Human nature and human enhancement Edit

The contemporary debate between so-called “bioconservatives” and “transhumanists” is directly related to the concept of human nature: transhumanists argue that "current human nature is improvable through the use of applied science and other rational methods." [97] Bioconservatives believe that the costs outweigh the benefits: in particular, they present their position as a defense of human nature which, according to them, is threatened by human enhancement technologies. Although this debate is mainly of an ethical kind, it is deeply rooted in the different interpretations of human nature, human freedom, and human dignity (which, according to bioconservatives, is specific to human beings, while transhumanists think that it can be possessed also by posthumans). As explained by Allen Buchanan, [98] the literature against human enhancement is characterized by two main concerns: that "enhancement may alter or destroy human nature" and that "if enhancement alters or destroys human nature, this will undercut our ability to ascertain the good," as "the good is determined by our nature." [98]

Bioconservatives include Jürgen Habermas, [99] Leon Kass, [100] Francis Fukuyama, [101] and Bill McKibben. [97] Some of the reasons why they oppose (certain forms of) human enhancement technology are to be found in the worry that such technology would be “dehumanizing” (as they would undermine the human dignity intrinsically built in our human nature). For instance, they fear that becoming “posthumans” could pose a threat to “ordinary” humans [102] or be harmful to posthumans themselves. [103] [97]

Jürgen Habermas makes the argument against the specific case of genetic modification of unborn children by their parents, referred to as “eugenic programming” by Habermas. His argument is two-folded: The most immediate threat is on the “ethical freedom” of programmed individuals, and the subsequent threat is on the viability of liberal democracy. Reasoning of the former can be formulated as the following: Genetic programming of desirable traits, capabilities and dispositions puts restrictions on a person's freedom to choose a life of his own, to be the sole author of his existence. A genetically-programmed child may feel alienated from his identity, which is now irreversibly co-written by human agents other than himself. This feeling of alienation, resulted from“contingency of a life's beginning that is not at [one's] disposal,” makes it difficult for genetically-modified persons to perceive themselves as moral agents who can make ethical judgement freely and independently - that is, without any substantial or definitive interference from another agent. Habermas proposes a second threat - the undermining power of genetic programming on the viability of democracy. The basis of liberal democracy, Habermas rightfully claims, is the symmetrical and independent mutual recognition among free, equal and autonomous persons. Genetic programming jeopardizes this condition by irreversibly subjecting children to permanent dependence on their parents, thus depriving them of their perceived ability to be full citizens of the legal community. This fundamental modification to human relationship erodes the foundation of liberal democracy and puts its viability in danger. [104]

The most famous proponent of transhumanism, on the other hand, is Oxford Swedish philosopher Nick Bostrom. According to Bostrom, "human enhancement technologies should be made widely available," [97] as they would offer enormous potential for improving the lives of human beings, without "dehumanizing" them: for instance, improving their intellectual and physical capacities, or protecting them from suffering, illnesses, aging, and physical and cognitive shortcomings. [97] In response to bioconservatives, transhumanists argue that expanding a person's "capability set" would increase her freedom of choice, rather than reducing it. [97]

Allen Buchanan has questioned the relevance of the concept of human nature to this debate. In "Human Nature and Enhancement", he argued that good but also bad characteristics are part of human nature, and that changing the "bad" ones does not necessarily imply that the "good" ones will be affected. Moreover, Buchanan argued that the way we evaluate the good is independent of human nature: in fact, we can "make coherent judgements about the defective aspects of human nature, and if those defects were readied this need not affect our ability to judge what is good". [98] Buchanan's conclusion is that the debate on enhancement of human beings would be more fruitful if it was conducted without appealing to the concept of human nature. [98]

Tim Lewens presented a similar position: since the only notions of human nature which are compatible with biology offer "no ethical guidance in debates over enhancement", we should set the concept of human nature aside when debating about enhancement. On the other hand, "folk", neo-Aristotelian conceptions of human nature seem to have normative implications, but they have no basis in scientific research. [105] Grant Ramsey replied to these claims, arguing that his "life-history trait cluster" account allows the concept of human nature "to inform questions of human enhancement". [106]

Appeals to nature often fall foul of the naturalistic fallacy, whereby certain capacities or traits are considered morally 'good' in virtue of their naturalness. The fallacy was initially introduced by G. E. Moore in 1903, who challenged philosopher's attempts to define good reductively, in terms of natural properties (such as desirable). Reliance on 'the natural' as a justification for resisting enhancement is criticised on several grounds by transhumanists, against the bioconservative motivation to preserve or protect 'human nature'.

For example, Nick Bostrom asserts "had Mother Nature been a real parent, she would have been in jail for child abuse and murder" [107] thus not worthy of unqualified protection. Similarly, Arthur Caplan opposes naturalistic objections to life extension enhancements, by claiming that: [108]

The explanation of why ageing occurs has many of the attributes of a stochastic or chance phenomenon. And this makes ageing unnatural and in no way an intrinsic part of human nature. As such, there is no reason why it is intrinsically wrong to try to reverse or cure ageing.

Instinctual behaviour Edit

Instinctual behaviour, an inherent inclination towards a particular complex behaviour, has been observed in humans. Emotions such as fear are part of human nature (see Fear § Innate fear for example). However they are also known to have been malleable and not fixed (see neuroplasticity and Fear § Inability to experience fear).

Congenital fear of snakes and spiders was found in six-month-old babies. [109] Infant cry is a manifestation of instinct. The infant cannot otherwise protect itself for survival during its long period of maturation. The maternal instinct, manifest particularly in response to the infant cry, has long been respected as one of the most powerful. Its mechanism has been partly elucidated by observations with functional MRI of the mother’s brain. [110]

The herd instinct is found in human children and chimpanzee cubs, but is apparently absent in the young orangutans. [111]

Squeamishness and disgust in humans is an instinct developed during evolution to protect the body and avoid infection by various diseases. [112]

Hormones can affect instinctual behaviour.

Hormones Edit

Testosterone (main male sex hormone) primes several instincts, especially sexuality also dominance, manifest in self-affirmation, the urge to win over rivals (see competitiveness), to dominate a hierarchy (see dominance hierarchy), and to respond to violent signals in men (see aggression), with weakening of empathy. [113] In men, a decrease in testosterone level after the birth of a child in the family was found, so that the father’s energies are more directed to nurturing, protecting and caring for the child. [114] [115] Unduly high levels of this hormone are often associated in a person with aggressiveness, illegal behavior, violence against others, such phenomena as banditry, etc. [ citation needed ] This is confirmed by studies conducted in prisons. [116] [117] The amount of testosterone in men may increase dramatically in response to any competition. [118] In men, the level of testosterone varies depending on whether it is susceptible to the smell of an ovulating or non-ovulatory woman (see menstrual cycle). Men exposed to the odors of ovulating women maintained a stable level of testosterone, which was higher than the level of testosterone in men exposed to non-ovulatory signals. This is due to the fact that an ovulating woman is capable of conceiving, and therefore a man who feels the smell of an ovulating woman is given a signal to sexual activity. [119]

Socioeconomic context Edit

The socioeconomic environment of humans are a context which affect their brain development. [120] It has been argued that H. sapiens is unsustainable by nature – that unsustainability is an inevitable emergent property of his unaltered nature. [121] It has also been argued that human nature is not necessarily resulting in unsustainability but is embedded in and affected by a socioeconomic system that is not having an inevitable structure [122] [ additional citation(s) needed ] – that the contemporary socioeconomic macrosystem affects human activities. [123] A paper published in 1997 concluded that humanity suffer consequences of a "poor fit" between inherited natures and "many of the constructed environments in organizational society". [124] Designing a "cultural narrative" explicitly for living on a finite planet may be suitable for overriding "outdated" innate tendencies. [121]

Human nature – which some have argued to vary to some extent per individual and in time, not be static and, at least in the future, to some extent be purposely alterable [125] – is one of the factors that shape which, how and when human activities are conducted. The contemporary socioeconomic and collective decision-making mechanisms are structures that may affect the expression of human nature – for instance, innate tendencies to seek survival, well-being, respect and status that some consider fundamental to humans [126] may result in varying product-designs, types of work, public infrastructure-designs and the distribution and prevalence of each. As with the nature versus nurture debate, which is concerned whether – or to which degrees – human behavior is determined by the environment or by a person's genes, scientific research is inconclusive about the degree to which human nature is shaped by and manageable by systemic structures as well as about how and to which degrees these structures can and should be purposely altered swiftly globally.


Contents

Before the 1980s, when it was unclear whether warming by greenhouse gases would dominate aerosol-induced cooling, scientists often used the term inadvertent climate modification to refer to humankind's impact on the climate. In the 1980s, the terms global warming and climate change were popularised, the former referring only to increased surface warming, while the latter describes the full effect of greenhouse gases on the climate. [20] Global warming became the most popular term after NASA climate scientist James Hansen used it in his 1988 testimony in the U.S. Senate. [21] In the 2000s, the term climate change increased in popularity. [22] Global warming usually refers to human-induced warming of the Earth system, whereas climate change can refer to natural as well as anthropogenic change. [23] The two terms are often used interchangeably. [24]

Various scientists, politicians and media figures have adopted the terms climate crisis or climate emergency to talk about climate change, while using global heating instead of global warming. [25] The policy editor-in-chief of The Guardian explained that they included this language in their editorial guidelines "to ensure that we are being scientifically precise, while also communicating clearly with readers on this very important issue". [26] Oxford Dictionary chose climate emergency as its word of the year in 2019 and defines the term as "a situation in which urgent action is required to reduce or halt climate change and avoid potentially irreversible environmental damage resulting from it". [27]

Multiple independently produced instrumental datasets show that the climate system is warming, [30] with the 2009–2018 decade being 0.93 ± 0.07 °C (1.67 ± 0.13 °F) warmer than the pre-industrial baseline (1850–1900). [31] Currently, surface temperatures are rising by about 0.2 °C (0.36 °F) per decade, [32] with 2020 reaching a temperature of 1.2 °C (2.2 °F) above pre-industrial. [13] Since 1950, the number of cold days and nights has decreased, and the number of warm days and nights has increased. [33]

There was little net warming between the 18th century and the mid-19th century. Climate proxies, sources of climate information from natural archives such as trees and ice cores, show that natural variations offset the early effects of the Industrial Revolution. [34] Thermometer records began to provide global coverage around 1850. [35] Historical patterns of warming and cooling, like the Medieval Climate Anomaly and the Little Ice Age, did not occur at the same time across different regions, but temperatures may have reached as high as those of the late-20th century in a limited set of regions. [36] There have been prehistorical episodes of global warming, such as the Paleocene–Eocene Thermal Maximum. [37] However, the modern observed rise in temperature and CO
2 concentrations has been so rapid that even abrupt geophysical events that took place in Earth's history do not approach current rates. [38]

Evidence of warming from air temperature measurements are reinforced with a wide range of other observations. [39] There has been an increase in the frequency and intensity of heavy precipitation, melting of snow and land ice, and increased atmospheric humidity. [40] Flora and fauna are also behaving in a manner consistent with warming for instance, plants are flowering earlier in spring. [41] Another key indicator is the cooling of the upper atmosphere, which demonstrates that greenhouse gases are trapping heat near the Earth's surface and preventing it from radiating into space. [42]

While locations of warming vary, the patterns are independent of where greenhouse gases are emitted, because the gases persist long enough to diffuse across the planet. Since the pre-industrial period, global average land temperatures have increased almost twice as fast as global average surface temperatures. [43] This is because of the larger heat capacity of oceans, and because oceans lose more heat by evaporation. [44] Over 90% of the additional energy in the climate system over the last 50 years has been stored in the ocean, with the remainder warming the atmosphere, melting ice, and warming the continents. [45] [46]

The Northern Hemisphere and the North Pole have warmed much faster than the South Pole and Southern Hemisphere. The Northern Hemisphere not only has much more land, but also more seasonal snow cover and sea ice, because of how the land masses are arranged around the Arctic Ocean. As these surfaces flip from reflecting a lot of light to being dark after the ice has melted, they start absorbing more heat. [47] Localised black carbon deposits on snow and ice also contribute to Arctic warming. [48] Arctic temperatures have increased and are predicted to continue to increase during this century at over twice the rate of the rest of the world. [49] Melting of glaciers and ice sheets in the Arctic disrupts ocean circulation, including a weakened Gulf Stream, further changing the climate. [50]

The climate system experiences various cycles on its own which can last for years (such as the El Niño–Southern Oscillation), decades or even centuries. [51] Other changes are caused by an imbalance of energy that is "external" to the climate system, but not always external to the Earth. [52] Examples of external forcings include changes in the composition of the atmosphere (e.g. increased concentrations of greenhouse gases), solar luminosity, volcanic eruptions, and variations in the Earth's orbit around the Sun. [53]

To determine the human contribution to climate change, known internal climate variability and natural external forcings need to be ruled out. A key approach is to determine unique "fingerprints" for all potential causes, then compare these fingerprints with observed patterns of climate change. [54] For example, solar forcing can be ruled out as a major cause because its fingerprint is warming in the entire atmosphere, and only the lower atmosphere has warmed, as expected from greenhouse gases (which trap heat energy radiating from the surface). [55] Attribution of recent climate change shows that the primary driver is elevated greenhouse gases, but that aerosols also have a strong effect. [56]

Greenhouse gases

The Earth absorbs sunlight, then radiates it as heat. Greenhouse gases in the atmosphere absorb and reemit infrared radiation, slowing the rate at which it can pass through the atmosphere and escape into space. [57] Before the Industrial Revolution, naturally-occurring amounts of greenhouse gases caused the air near the surface to be about 33 °C (59 °F) warmer than it would have been in their absence. [58] [59] While water vapour (

25%) are the biggest contributors to the greenhouse effect, they increase as a function of temperature and are therefore considered feedbacks. On the other hand, concentrations of gases such as CO
2 (

20%), tropospheric ozone, [60] CFCs and nitrous oxide are not temperature-dependent, and are therefor considered external forcings. [61]

Human activity since the Industrial Revolution, mainly extracting and burning fossil fuels (coal, oil, and natural gas), [62] has increased the amount of greenhouse gases in the atmosphere, resulting in a radiative imbalance. In 2018, the concentrations of CO
2 and methane had increased by about 45% and 160%, respectively, since 1750. [63] These CO
2 levels are much higher than they have been at any time during the last 800,000 years, the period for which reliable data have been collected from air trapped in ice cores. [64] Less direct geological evidence indicates that CO
2 values have not been this high for millions of years. [65]

Global anthropogenic greenhouse gas emissions in 2018, excluding those from land use change, were equivalent to 52 billion tonnes of CO
2 . Of these emissions, 72% was actual CO
2 , 19% was methane, 6% was nitrous oxide, and 3% was fluorinated gases. [3] CO
2 emissions primarily come from burning fossil fuels to provide energy for transport, manufacturing, heating, and electricity. [66] Additional CO
2 emissions come from deforestation and industrial processes, which include the CO
2 released by the chemical reactions for making cement, steel, aluminum, and fertiliser. [67] Methane emissions come from livestock, manure, rice cultivation, landfills, wastewater, coal mining, as well as oil and gas extraction. [68] Nitrous oxide emissions largely come from the microbial decomposition of inorganic and organic fertiliser. [69] From a production standpoint, the primary sources of global greenhouse gas emissions are estimated as: electricity and heat (25%), agriculture and forestry (24%), industry and manufacturing (21%), transport (14%), and buildings (6%). [70]

Despite the contribution of deforestation to greenhouse gas emissions, the Earth's land surface, particularly its forests, remain a significant carbon sink for CO
2 . Natural processes, such as carbon fixation in the soil and photosynthesis, more than offset the greenhouse gas contributions from deforestation. The land-surface sink is estimated to remove about 29% of annual global CO
2 emissions. [71] The ocean also serves as a significant carbon sink via a two-step process. First, CO
2 dissolves in the surface water. Afterwards, the ocean's overturning circulation distributes it deep into the ocean's interior, where it accumulates over time as part of the carbon cycle. Over the last two decades, the world's oceans have absorbed 20 to 30% of emitted CO
2 . [72]

Aerosols and clouds

Air pollution, in the form of aerosols, not only puts a large burden on human health, but also affects the climate on a large scale. [73] From 1961 to 1990, a gradual reduction in the amount of sunlight reaching the Earth's surface was observed, a phenomenon popularly known as global dimming, [74] typically attributed to aerosols from biofuel and fossil fuel burning. [75] Aerosol removal by precipitation gives tropospheric aerosols an atmospheric lifetime of only about a week, while stratospheric aerosols can remain in the atmosphere for a few years. [76] Globally, aerosols have been declining since 1990, meaning that they no longer mask greenhouse gas warming as much. [77]

In addition to their direct effects (scattering and absorbing solar radiation), aerosols have indirect effects on the Earth's radiation budget. Sulfate aerosols act as cloud condensation nuclei and thus lead to clouds that have more and smaller cloud droplets. These clouds reflect solar radiation more efficiently than clouds with fewer and larger droplets. [78] This effect also causes droplets to be more uniform in size, which reduces the growth of raindrops and makes clouds more reflective to incoming sunlight. [79] Indirect effects of aerosols are the largest uncertainty in radiative forcing. [80]

While aerosols typically limit global warming by reflecting sunlight, black carbon in soot that falls on snow or ice can contribute to global warming. Not only does this increase the absorption of sunlight, it also increases melting and sea-level rise. [81] Limiting new black carbon deposits in the Arctic could reduce global warming by 0.2 °C (0.36 °F) by 2050. [82]

Changes of the land surface

Humans change the Earth's surface mainly to create more agricultural land. Today, agriculture takes up 34% of Earth's land area, while 26% is forests, and 30% is uninhabitable (glaciers, deserts, etc.). [84] The amount of forested land continues to decrease, largely due to conversion to cropland in the tropics. [85] This deforestation is the most significant aspect of land surface change affecting global warming. The main causes of deforestation are: permanent land-use change from forest to agricultural land producing products such as beef and palm oil (27%), logging to produce forestry/forest products (26%), short term shifting cultivation (24%), and wildfires (23%). [86]

In addition to affecting greenhouse gas concentrations, land-use changes affect global warming through a variety of other chemical and physical mechanisms. Changing the type of vegetation in a region affects the local temperature, by changing how much of the sunlight gets reflected back into space (albedo), and how much heat is lost by evaporation. For instance, the change from a dark forest to grassland makes the surface lighter, causing it to reflect more sunlight. Deforestation can also contribute to changing temperatures by affecting the release of aerosols and other chemical compounds that influence clouds, and by changing wind patterns. [87] In tropic and temperate areas the net effect is to produce significant warming, while at latitudes closer to the poles a gain of albedo (as forest is replaced by snow cover) leads to an overall cooling effect. [87] Globally, these effects are estimated to have led to a slight cooling, dominated by an increase in surface albedo. [88]

Solar and volcanic activity

Physical climate models are unable to reproduce the rapid warming observed in recent decades when taking into account only variations in solar output and volcanic activity. [89] As the Sun is the Earth's primary energy source, changes in incoming sunlight directly affect the climate system. [90] Solar irradiance has been measured directly by satellites, [91] and indirect measurements are available from the early 1600s. [90] There has been no upward trend in the amount of the Sun's energy reaching the Earth. [92] Further evidence for greenhouse gases being the cause of recent climate change come from measurements showing the warming of the lower atmosphere (the troposphere), coupled with the cooling of the upper atmosphere (the stratosphere). [93] If solar variations were responsible for the observed warming, warming of both the troposphere and the stratosphere would be expected, but that has not been the case. [55]

Explosive volcanic eruptions represent the largest natural forcing over the industrial era. When the eruption is sufficiently strong (with sulfur dioxide reaching the stratosphere) sunlight can be partially blocked for a couple of years, with a temperature signal lasting about twice as long. In the industrial era, volcanic activity has had negligible impacts on global temperature trends. [94] Present-day volcanic CO2 emissions are equivalent to less than 1% of current anthropogenic CO2 emissions. [95]

Climate change feedback

The response of the climate system to an initial forcing is modified by feedbacks: increased by self-reinforcing feedbacks and reduced by balancing feedbacks. [97] The main reinforcing feedbacks are the water-vapour feedback, the ice–albedo feedback, and probably the net effect of clouds. [98] The primary balancing feedback to global temperature change is radiative cooling to space as infrared radiation in response to rising surface temperature. [99] In addition to temperature feedbacks, there are feedbacks in the carbon cycle, such as the fertilizing effect of CO
2 on plant growth. [100] Uncertainty over feedbacks is the major reason why different climate models project different magnitudes of warming for a given amount of emissions. [101]

As air gets warmer, it can hold more moisture. After initial warming due to emissions of greenhouse gases, the atmosphere will hold more water. As water vapour is a potent greenhouse gas, this further heats the atmosphere. [98] If cloud cover increases, more sunlight will be reflected back into space, cooling the planet. If clouds become more high and thin, they act as an insulator, reflecting heat from below back downwards and warming the planet. [102] Overall, the net cloud feedback over the industrial era has probably exacerbated temperature rise. [103] The reduction of snow cover and sea ice in the Arctic reduces the albedo of the Earth's surface. [104] More of the Sun's energy is now absorbed in these regions, contributing to amplification of Arctic temperature changes. [105] Arctic amplification is also melting permafrost, which releases methane and CO
2 into the atmosphere. [106]

Around half of human-caused CO
2 emissions have been absorbed by land plants and by the oceans. [107] On land, elevated CO
2 and an extended growing season have stimulated plant growth. Climate change increases droughts and heat waves that inhibit plant growth, which makes it uncertain whether this carbon sink will continue to grow in the future. [108] Soils contain large quantities of carbon and may release some when they heat up. [109] As more CO
2 and heat are absorbed by the ocean, it acidifies, its circulation changes and phytoplankton takes up less carbon, decreasing the rate at which the ocean absorbs atmospheric carbon. [110] Climate change can increase methane emissions from wetlands, marine and freshwater systems, and permafrost. [111]

Future warming depends on the strengths of climate feedbacks and on emissions of greenhouse gases. [112] The former are often estimated using various climate models, developed by multiple scientific institutions. [113] A climate model is a representation of the physical, chemical, and biological processes that affect the climate system. [114] Models include changes in the Earth's orbit, historical changes in the Sun's activity, and volcanic forcing. [115] Computer models attempt to reproduce and predict the circulation of the oceans, the annual cycle of the seasons, and the flows of carbon between the land surface and the atmosphere. [116] Models project different future temperature rises for given emissions of greenhouse gases they also do not fully agree on the strength of different feedbacks on climate sensitivity and magnitude of inertia of the climate system. [117]

The physical realism of models is tested by examining their ability to simulate contemporary or past climates. [118] Past models have underestimated the rate of Arctic shrinkage [119] and underestimated the rate of precipitation increase. [120] Sea level rise since 1990 was underestimated in older models, but more recent models agree well with observations. [121] The 2017 United States-published National Climate Assessment notes that "climate models may still be underestimating or missing relevant feedback processes". [122]

Various Representative Concentration Pathways (RCPs) can be used as input for climate models: "a stringent mitigation scenario (RCP2.6), two intermediate scenarios (RCP4.5 and RCP6.0) and one scenario with very high [greenhouse gas] emissions (RCP8.5)". [123] RCPs only look at concentrations of greenhouse gases, and so do not include the response of the carbon cycle. [124] Climate model projections summarised in the IPCC Fifth Assessment Report indicate that, during the 21st century, the global surface temperature is likely to rise a further 0.3 to 1.7 °C (0.5 to 3.1 °F) in a moderate scenario, or as much as 2.6 to 4.8 °C (4.7 to 8.6 °F) in an extreme scenario, depending on the rate of future greenhouse gas emissions and on climate feedback effects. [125]

A subset of climate models add societal factors to a simple physical climate model. These models simulate how population, economic growth, and energy use affect – and interact with – the physical climate. With this information, these models can produce scenarios of how greenhouse gas emissions may vary in the future. This output is then used as input for physical climate models to generate climate change projections. [126] In some scenarios emissions continue to rise over the century, while others have reduced emissions. [127] Fossil fuel resources are too abundant for shortages to be relied on to limit carbon emissions in the 21st century. [128] Emissions scenarios can be combined with modelling of the carbon cycle to predict how atmospheric concentrations of greenhouse gases might change in the future. [129] According to these combined models, by 2100 the atmospheric concentration of CO2 could be as low as 380 or as high as 1400 ppm, depending on the socioeconomic scenario and the mitigation scenario. [130]

The remaining carbon emissions budget is determined by modelling the carbon cycle and the climate sensitivity to greenhouse gases. [131] According to the IPCC, global warming can be kept below 1.5 °C (2.7 °F) with a two-thirds chance if emissions after 2018 do not exceed 420 or 570 gigatonnes of CO
2 , depending on exactly how the global temperature is defined. This amount corresponds to 10 to 13 years of current emissions. There are high uncertainties about the budget for instance, it may be 100 gigatonnes of CO
2 smaller due to methane release from permafrost and wetlands. [132]

Physical environment

The environmental effects of climate change are broad and far-reaching, affecting oceans, ice, and weather. Changes may occur gradually or rapidly. Evidence for these effects comes from studying climate change in the past, from modelling, and from modern observations. [134] Since the 1950s, droughts and heat waves have appeared simultaneously with increasing frequency. [135] Extremely wet or dry events within the monsoon period have increased in India and East Asia. [136] The maximum rainfall and wind speed from hurricanes and typhoons is likely increasing. [8] Frequency of tropical cyclones has not increased as a result of climate change. [137] While tornado and severe thunderstorm frequency has not increased as a result of climate change, the areas affected by such phenomena may be changing. [138]

Global sea level is rising as a consequence of glacial melt, melt of the ice sheets in Greenland and Antarctica, and thermal expansion. Between 1993 and 2017, the rise increased over time, averaging 3.1 ± 0.3 mm per year. [139] Over the 21st century, the IPCC projects that in a very high emissions scenario the sea level could rise by 61–110 cm. [140] Increased ocean warmth is undermining and threatening to unplug Antarctic glacier outlets, risking a large melt of the ice sheet [141] and the possibility of a 2-meter sea level rise by 2100 under high emissions. [142]

Climate change has led to decades of shrinking and thinning of the Arctic sea ice, making it vulnerable to atmospheric anomalies. [143] While ice-free summers are expected to be rare at 1.5 °C (2.7 °F) degrees of warming, they are set to occur once every three to ten years at a warming level of 2.0 °C (3.6 °F). [144] Higher atmospheric CO
2 concentrations have led to changes in ocean chemistry. An increase in dissolved CO
2 is causing oceans to acidify. [145] In addition, oxygen levels are decreasing as oxygen is less soluble in warmer water, [146] with hypoxic dead zones expanding as a result of algal blooms stimulated by higher temperatures, higher CO
2 levels, ocean deoxygenation, and eutrophication. [147]

Tipping points and long-term impacts

The greater the amount of global warming, the greater the risk of passing through ‘tipping points’, thresholds beyond which certain impacts can no longer be avoided even if temperatures are reduced. [148] An example is the collapse of West Antarctic and Greenland ice sheets, where a temperature rise of 1.5 to 2.0 °C (2.7 to 3.6 °F) may commit the ice sheets to melt, although the time scale of melt is uncertain and depends on future warming. [149] [14] Some large-scale changes could occur over a short time period, such as a collapse of the Atlantic Meridional Overturning Circulation, [150] which would trigger major climate changes in the North Atlantic, Europe, and North America. [151]

The long-term effects of climate change include further ice melt, ocean warming, sea level rise, and ocean acidification. On the timescale of centuries to millennia, the magnitude of climate change will be determined primarily by anthropogenic CO
2 emissions. [152] This is due to CO
2 's long atmospheric lifetime. [152] Oceanic CO
2 uptake is slow enough that ocean acidification will continue for hundreds to thousands of years. [153] These emissions are estimated to have prolonged the current interglacial period by at least 100,000 years. [154] Sea level rise will continue over many centuries, with an estimated rise of 2.3 metres per degree Celsius (4.2 ft/°F) after 2000 years. [155]

Nature and wildlife

Recent warming has driven many terrestrial and freshwater species poleward and towards higher altitudes. [156] Higher atmospheric CO
2 levels and an extended growing season have resulted in global greening, whereas heatwaves and drought have reduced ecosystem productivity in some regions. The future balance of these opposing effects is unclear. [157] Climate change has contributed to the expansion of drier climate zones, such as the expansion of deserts in the subtropics. [158] The size and speed of global warming is making abrupt changes in ecosystems more likely. [159] Overall, it is expected that climate change will result in the extinction of many species. [160]

The oceans have heated more slowly than the land, but plants and animals in the ocean have migrated towards the colder poles faster than species on land. [161] Just as on land, heat waves in the ocean occur more frequently due to climate change, with harmful effects found on a wide range of organisms such as corals, kelp, and seabirds. [162] Ocean acidification is impacting organisms who produce shells and skeletons, such as mussels and barnacles, and coral reefs coral reefs have seen extensive bleaching after heat waves. [163] Harmful algae bloom enhanced by climate change and eutrophication cause anoxia, disruption of food webs and massive large-scale mortality of marine life. [164] Coastal ecosystems are under particular stress, with almost half of wetlands having disappeared as a consequence of climate change and other human impacts. [165]

Ecological collapse. Bleaching has damaged the Great Barrier Reef and threatens reefs worldwide. [166]

Habitat destruction. Many arctic animals rely on sea ice, which has been disappearing in a warming Arctic. [168]

Pest propagation. Mild winters allow more pine beetles to survive to kill large swaths of forest. [169]

Humans

The effects of climate change on humans, mostly due to warming and shifts in precipitation, have been detected worldwide. Regional impacts of climate change are now observable on all continents and across ocean regions, [170] with low-latitude, less developed areas facing the greatest risk. [171] Continued emission of greenhouse gases will lead to further warming and long-lasting changes in the climate system, with potentially “severe, pervasive and irreversible impacts” for both people and ecosystems. [172] Climate change risks are unevenly distributed, but are generally greater for disadvantaged people in developing and developed countries. [173]

Food and health

Health impacts include both the direct effects of extreme weather, leading to injury and loss of life, [174] as well as indirect effects, such as undernutrition brought on by crop failures. [175] Various infectious diseases are more easily transmitted in a warmer climate, such as dengue fever, which affects children most severely, and malaria. [176] Young children are the most vulnerable to food shortages, and together with older people, to extreme heat. [177] The World Health Organization (WHO) has estimated that between 2030 and 2050, climate change is expected to cause approximately 250,000 additional deaths per year from heat exposure in elderly people, increases in diarrheal disease, malaria, dengue, coastal flooding, and childhood undernutrition. [178] Over 500,000 additional adult deaths are projected yearly by 2050 due to reductions in food availability and quality. [179] Other major health risks associated with climate change include air and water quality. [180] The WHO has classified human impacts from climate change as the greatest threat to global health in the 21st century. [181]

Climate change is affecting food security and has caused reduction in global mean yields of maize, wheat, and soybeans between 1981 and 2010. [182] Future warming could further reduce global yields of major crops. [183] Crop production will probably be negatively affected in low-latitude countries, while effects at northern latitudes may be positive or negative. [184] Up to an additional 183 million people worldwide, particularly those with lower incomes, are at risk of hunger as a consequence of these impacts. [185] The effects of warming on the oceans impact fish stocks, with a global decline in the maximum catch potential. Only polar stocks are showing an increased potential. [186] Regions dependent on glacier water, regions that are already dry, and small islands are at increased risk of water stress due to climate change. [187]

Livelihoods

Economic damages due to climate change have been underestimated, and may be severe, with the probability of disastrous tail-risk events being nontrivial. [188] Climate change has likely already increased global economic inequality, and is projected to continue doing so. [189] Most of the severe impacts are expected in sub-Saharan Africa and South-East Asia, where existing poverty is already exacerbated. [190] The World Bank estimates that climate change could drive over 120 million people into poverty by 2030. [191] Current inequalities between men and women, between rich and poor, and between different ethnicities have been observed to worsen as a consequence of climate variability and climate change. [192] An expert elicitation concluded that the role of climate change in armed conflict has been small compared to factors such as socio-economic inequality and state capabilities, but that future warming will bring increasing risks. [193]

Low-lying islands and coastal communities are threatened through hazards posed by sea level rise, such as flooding and permanent submergence. [194] This could lead to statelessness for populations in island nations, such as the Maldives and Tuvalu. [195] In some regions, rise in temperature and humidity may be too severe for humans to adapt to. [196] With worst-case climate change, models project that almost one-third of humanity might live in extremely hot and uninhabitable climates, similar to the current climate found mainly in the Sahara. [197] These factors, plus weather extremes, can drive environmental migration, both within and between countries. [198] Displacement of people is expected to increase as a consequence of more frequent extreme weather, sea level rise, and conflict arising from increased competition over natural resources. Climate change may also increase vulnerabilities, leading to "trapped populations" in some areas who are not able to move due to a lack of resources. [199]

Environmental migration. Sparser rainfall leads to desertification that harms agriculture and can displace populations. Shown: Telly, Mali. [200]

Agricultural changes. Droughts, rising temperatures, and extreme weather negatively impact agriculture. Shown: Texas, US. [201]

Tidal flooding. Sea-level rise increases flooding in low-lying coastal regions. Shown: Venice, Italy. [202]

Storm intensification. Bangladesh after Cyclone Sidr is an example of catastrophic flooding from increased rainfall. [203]

Heat wave intensification. Events like the June 2019 European heat wave are becoming more common. [204]

Mitigation

Climate change impacts can be mitigated by reducing greenhouse gas emissions and by enhancing sinks that absorb greenhouse gases from the atmosphere. [205] In order to limit global warming to less than 1.5 °C with a high likelihood of success, global greenhouse gas emissions needs to be net-zero by 2050, or by 2070 with a 2 °C target. [206] This requires far-reaching, systemic changes on an unprecedented scale in energy, land, cities, transport, buildings, and industry. [207] Scenarios that limit global warming to 1.5 °C often describe reaching net negative emissions at some point. [208] To make progress towards a goal of limiting warming to 2 °C, the United Nations Environment Programme estimates that, within the next decade, countries need to triple the amount of reductions they have committed to in their current Paris Agreements an even greater level of reduction is required to meet the 1.5 °C goal. [209]

Although there is no single pathway to limit global warming to 1.5 or 2.0 °C (2.7 or 3.6 °F), [210] most scenarios and strategies see a major increase in the use of renewable energy in combination with increased energy efficiency measures to generate the needed greenhouse gas reductions. [211] To reduce pressures on ecosystems and enhance their carbon sequestration capabilities, changes would also be necessary in sectors such as forestry and agriculture. [212]

Other approaches to mitigating climate change entail a higher level of risk. Scenarios that limit global warming to 1.5 °C typically project the large-scale use of carbon dioxide removal methods over the 21st century. [213] There are concerns, though, about over-reliance on these technologies, as well as possible environmental impacts. [214] Solar radiation management (SRM) methods have also been explored as a possible supplement to deep reductions in emissions. However, SRM would raise significant ethical and legal issues, and the risks are poorly understood. [215]

Clean energy

Long-term decarbonisation scenarios point to rapid and significant investment in renewable energy, [217] which includes solar and wind power, bioenergy, geothermal energy, and hydropower. [218] Fossil fuels accounted for 80% of the world's energy in 2018, while the remaining share was split between nuclear power and renewables [219] that mix is projected to change significantly over the next 30 years. [211] Solar and wind have seen substantial growth and progress over the last few years photovoltaic solar and onshore wind are the cheapest forms of adding new power generation capacity in most countries. [220] Renewables represented 75% of all new electricity generation installed in 2019, with solar and wind constituting nearly all of that amount. [221] Meanwhile, nuclear power costs are increasing amidst stagnant power share, so that nuclear power generation is now several times more expensive per megawatt-hour than wind and solar. [222]

To achieve carbon neutrality by 2050, renewable energy would become the dominant form of electricity generation, rising to 85% or more by 2050 in some scenarios. The use of electricity for other needs, such as heating, would rise to the point where electricity becomes the largest form of overall energy supply. [223] Investment in coal would be eliminated and coal use nearly phased out by 2050. [224]

In transport, scenarios envision sharp increases in the market share of electric vehicles, and low carbon fuel substitution for other transportation modes like shipping. [225] Building heating would be increasingly decarbonized with the use of technologies like heat pumps. [226]

There are obstacles to the continued rapid development of renewables. For solar and wind power, a key challenge is their intermittency and seasonal variability. Traditionally, hydro dams with reservoirs and conventional power plants have been used when variable energy production is low. Intermittency can further be countered by demand flexibility, and by expanding battery storage and long-distance transmission to smooth variability of renewable output across wider geographic areas. [217] Some environmental and land use concerns have been associated with large solar and wind projects, [227] while bioenergy is often not carbon neutral and may have negative consequences for food security. [228] Hydropower growth has been slowing and is set to decline further due to concerns about social and environmental impacts. [229]

Clean energy improves human health by minimizing climate change and has the near-term benefit of reducing air pollution deaths, [230] which were estimated at 7 million annually in 2016. [231] Meeting the Paris Agreement goals that limit warming to a 2 °C increase could save about a million of those lives per year by 2050, whereas limiting global warming to 1.5 °C could save millions and simultaneously increase energy security and reduce poverty. [232]

Energy efficiency

Reducing energy demand is another major feature of decarbonisation scenarios and plans. [233] In addition to directly reducing emissions, energy demand reduction measures provide more flexibility for low carbon energy development, aid in the management of the electricity grid, and minimise carbon-intensive infrastructure development. [234] Over the next few decades, major increases in energy efficiency investment will be required to achieve these reductions, comparable to the expected level of investment in renewable energy. [235] However, several COVID-19 related changes in energy use patterns, energy efficiency investments, and funding have made forecasts for this decade more difficult and uncertain. [236]

Efficiency strategies to reduce energy demand vary by sector. In transport, gains can be made by switching passengers and freight to more efficient travel modes, such as buses and trains, and increasing the use of electric vehicles. [237] Industrial strategies to reduce energy demand include increasing the energy efficiency of heating systems and motors, designing less energy-intensive products, and increasing product lifetimes. [238] In the building sector the focus is on better design of new buildings, and incorporating higher levels of energy efficiency in retrofitting techniques for existing structures. [239] In addition to decarbonizing energy use, the use of technologies like heat pumps can also increase building energy efficiency. [240]

Agriculture and industry

Agriculture and forestry face a triple challenge of limiting greenhouse gas emissions, preventing the further conversion of forests to agricultural land, and meeting increases in world food demand. [241] A suite of actions could reduce agriculture/forestry-based greenhouse gas emissions by 66% from 2010 levels by reducing growth in demand for food and other agricultural products, increasing land productivity, protecting and restoring forests, and reducing greenhouse gas emissions from agricultural production. [242]

In addition to the industrial demand reduction measures mentioned earlier, steel and cement production, which together are responsible for about 13% of industrial CO
2 emissions, present particular challenges. In these industries, carbon-intensive materials such as coke and lime play an integral role in the production process. Reducing CO
2 emissions here requires research driven efforts aimed at decarbonizing the chemistry of these processes. [243]

Carbon sequestration

Natural carbon sinks can be enhanced to sequester significantly larger amounts of CO
2 beyond naturally occurring levels. [244] Reforestation and tree planting on non-forest lands are among the most mature sequestration techniques, although they raise food security concerns. Soil carbon sequestration and coastal carbon sequestration are less understood options. [245] The feasibility of land-based negative emissions methods for mitigation are uncertain in models the IPCC has described mitigation strategies based on them as risky. [246]

Where energy production or CO
2 -intensive heavy industries continue to produce waste CO
2 , the gas can be captured and stored instead of being released to the atmosphere. Although its current use is limited in scale and expensive, [247] carbon capture and storage (CCS) may be able to play a significant role in limiting CO
2 emissions by mid-century. [248] This technique, in combination with bio-energy production (BECCS) can result in net-negative emissions, where the amount of greenhouse gasses that are released into the atmosphere are less than the sequestered, or stored, amount in the bio-energy fuel being grown. [249] It remains highly uncertain whether carbon dioxide removal techniques, such as BECCS, will be able to play a large role in limiting warming to 1.5 °C, and policy decisions based on reliance on carbon dioxide removal increases the risk of global warming increasing beyond international goals. [250]

Adaptation

Adaptation is "the process of adjustment to current or expected changes in climate and its effects". [251] Without additional mitigation, adaptation cannot avert the risk of "severe, widespread and irreversible" impacts. [252] More severe climate change requires more transformative adaptation, which can be prohibitively expensive. [251] The capacity and potential for humans to adapt, called adaptive capacity, is unevenly distributed across different regions and populations, and developing countries generally have less. [253] The first two decades of the 21st century saw an increase in adaptive capacity in most low- and middle-income countries with improved access to basic sanitation and electricity, but progress is slow. Many countries have implemented adaptation policies. However, there is a considerable gap between necessary and available finance. [254]

Adaptation to sea level rise consists of avoiding at-risk areas, learning to live with increased flooding, protection and, if needed, the more transformative option of managed retreat. [255] There are economic barriers for moderation of dangerous heat impact: avoiding strenuous work or employing private air conditioning is not possible for everybody. [256] In agriculture, adaptation options include a switch to more sustainable diets, diversification, erosion control and genetic improvements for increased tolerance to a changing climate. [257] Insurance allows for risk-sharing, but is often difficult to obtain for people on lower incomes. [258] Education, migration and early warning systems can reduce climate vulnerability. [259]

Ecosystems adapt to climate change, a process that can be supported by human intervention. Possible responses include increasing connectivity between ecosystems, allowing species to migrate to more favourable climate conditions and species relocation. Protection and restoration of natural and semi-natural areas helps build resilience, making it easier for ecosystems to adapt. Many of the actions that promote adaptation in ecosystems, also help humans adapt via ecosystem-based adaptation. For instance, restoration of natural fire regimes makes catastrophic fires less likely, and reduces human exposure. Giving rivers more space allows for more water storage in the natural system, reducing flood risk. Restored forest act as a carbon sink, but planting trees in unsuitable regions can exacerbate climate impacts. [260]

There are some synergies and trade-offs between adaptation and mitigation. Adaptation measures often offer short-term benefits, whereas mitigation has longer-term benefits. [261] Increased use of air conditioning allows people to better cope with heat, but increases energy demand. Compact urban development may lead to reduced emissions from transport and construction. Simultaneously, it may increase the urban heat island effect, leading to higher temperatures and increased exposure. [262] Increased food productivity has large benefits for both adaptation and mitigation. [263]

Countries that are most vulnerable to climate change have typically been responsible for a small share of global emissions, which raises questions about justice and fairness. [264] Climate change is strongly linked to sustainable development. Limiting global warming makes it easier to achieve sustainable development goals, such as eradicating poverty and reducing inequalities. The connection between the two is recognised in the Sustainable Development Goal 13 which is to "Take urgent action to combat climate change and its impacts". [265] The goals on food, clean water and ecosystem protections have synergies with climate mitigation. [266]

The geopolitics of climate change is complex and has often been framed as a free-rider problem, in which all countries benefit from mitigation done by other countries, but individual countries would lose from investing in a transition to a low-carbon economy themselves. This framing has been challenged. For instance, the benefits in terms of public health and local environmental improvements of coal phase-out exceed the costs in almost all regions. [267] Another argument against this framing is that net importers of fossil fuels win economically from transitioning, causing net exporters to face stranded assets: fossil fuels they cannot sell. [268]

Policy options

A wide range of policies, regulations and laws are being used to reduce greenhouse gases. Carbon pricing mechanisms include carbon taxes and emissions trading systems. [269] As of 2019, carbon pricing covers about 20% of global greenhouse gas emissions. [270] Direct global fossil fuel subsidies reached $319 billion in 2017, and $5.2 trillion when indirect costs such as air pollution are priced in. [271] Ending these can cause a 28% reduction in global carbon emissions and a 46% reduction in air pollution deaths. [272] Subsidies could also be redirected to support the transition to clean energy. [273] More prescriptive methods that can reduce greenhouse gases include vehicle efficiency standards, renewable fuel standards, and air pollution regulations on heavy industry. [274] Renewable portfolio standards have been enacted in several countries requiring utilities to increase the percentage of electricity they generate from renewable sources. [275]

As the use of fossil fuels is reduced, there are Just Transition considerations involving the social and economic challenges that arise. An example is the employment of workers in the affected industries, along with the well-being of the broader communities involved. [276] Climate justice considerations, such as those facing indigenous populations in the Arctic, [277] are another important aspect of mitigation policies. [278]

International climate agreements

Nearly all countries in the world are parties to the 1994 United Nations Framework Convention on Climate Change (UNFCCC). [280] The objective of the UNFCCC is to prevent dangerous human interference with the climate system. [281] As stated in the convention, this requires that greenhouse gas concentrations are stabilised in the atmosphere at a level where ecosystems can adapt naturally to climate change, food production is not threatened, and economic development can be sustained. [282] Global emissions have risen since signing of the UNFCCC, which does not actually restrict emissions but rather provides a framework for protocols that do. [70] Its yearly conferences are the stage of global negotiations. [283]

The 1997 Kyoto Protocol extended the UNFCCC and included legally binding commitments for most developed countries to limit their emissions, [284] During Kyoto Protocol negotiations, the G77 (representing developing countries) pushed for a mandate requiring developed countries to "[take] the lead" in reducing their emissions, [285] since developed countries contributed most to the accumulation of greenhouse gases in the atmosphere, and since per-capita emissions were still relatively low in developing countries and emissions of developing countries would grow to meet their development needs. [286]

The 2009 Copenhagen Accord has been widely portrayed as disappointing because of its low goals, and was rejected by poorer nations including the G77. [287] Associated parties aimed to limit the increase in global mean temperature to below 2.0 °C (3.6 °F). [288] The Accord set the goal of sending $100 billion per year to developing countries in assistance for mitigation and adaptation by 2020, and proposed the founding of the Green Climate Fund. [289] As of 2020 [update] , the fund has failed to reach its expected target, and risks a shrinkage in its funding. [290]

In 2015 all UN countries negotiated the Paris Agreement, which aims to keep global warming well below 1.5 °C (2.7 °F) and contains an aspirational goal of keeping warming under 1.5 °C . [291] The agreement replaced the Kyoto Protocol. Unlike Kyoto, no binding emission targets were set in the Paris Agreement. Instead, the procedure of regularly setting ever more ambitious goals and reevaluating these goals every five years has been made binding. [292] The Paris Agreement reiterated that developing countries must be financially supported. [293] As of February 2021 [update] , 194 states and the European Union have signed the treaty and 188 states and the EU have ratified or acceded to the agreement. [294]

The 1987 Montreal Protocol, an international agreement to stop emitting ozone-depleting gases, may have been more effective at curbing greenhouse gas emissions than the Kyoto Protocol specifically designed to do so. [295] The 2016 Kigali Amendment to the Montreal Protocol aims to reduce the emissions of hydrofluorocarbons, a group of powerful greenhouse gases which served as a replacement for banned ozone-depleting gases. This strengthened the makes the Montreal Protocol a stronger agreement against climate change. [296]

National responses

In 2019, the United Kingdom parliament became the first national government in the world to officially declare a climate emergency. [297] Other countries and jurisdictions followed suit. [298] In November 2019 the European Parliament declared a "climate and environmental emergency", [299] and the European Commission presented its European Green Deal with the goal of making the EU carbon-neutral by 2050. [300] Major countries in Asia have made similar pledges: South Korea and Japan have committed to become carbon neutral by 2050, and China by 2060. [301]

As of 2021, based on information from 48 NDCs which represent 40% of the parties to the Paris Agreement, estimated total greenhouse gas emissions will be 0.5% lower compared to 2010 levels, below the 45% or 25% reduction goals to limit global warming to 1.5 °C or 2 °C, respectively. [302]

Scientific consensus

There is an overwhelming scientific consensus that global surface temperatures have increased in recent decades and that the trend is caused mainly by human-induced emissions of greenhouse gases, with 90–100% (depending on the exact question, timing and sampling methodology) of publishing climate scientists agreeing. [304] The consensus has grown to 100% among research scientists on anthropogenic global warming as of 2019. [305] No scientific body of national or international standing disagrees with this view. [306] Consensus has further developed that some form of action should be taken to protect people against the impacts of climate change, and national science academies have called on world leaders to cut global emissions. [307]

Scientific discussion takes place in journal articles that are peer-reviewed, which scientists subject to assessment every couple of years in the Intergovernmental Panel on Climate Change reports. [308] In 2013, the IPCC Fifth Assessment Report stated that "it is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century". [309] Their 2018 report expressed the scientific consensus as: "human influence on climate has been the dominant cause of observed warming since the mid-20th century". [310] Scientists have issued two warnings to humanity, in 2017 and 2019, expressing concern about the current trajectory of potentially catastrophic climate change, and about untold human suffering as a consequence. [311]

The public

Climate change came to international public attention in the late 1980s. [312] Due to confusing media coverage in the early 1990s, understanding was often confounded by conflation with other environmental issues like ozone depletion. [313] In popular culture, the first movie to reach a mass public on the topic was The Day After Tomorrow in 2004, followed a few years later by the Al Gore documentary An Inconvenient Truth. Books, stories and films about climate change fall under the genre of climate fiction. [312]

Significant regional differences exist in both public concern for and public understanding of climate change. In 2015, a median of 54% of respondents considered it "a very serious problem", but Americans and Chinese (whose economies are responsible for the greatest annual CO2 emissions) were among the least concerned. [314] A 2018 survey found increased concern globally on the issue compared to 2013 in most countries. More highly educated people, and in some countries, women and younger people were more likely to see climate change as a serious threat. In the United States, there was a large partisan gap in opinion. [315]

Denial and misinformation

Public debate about climate change has been strongly affected by climate change denial and misinformation, which originated in the United States and has since spread to other countries, particularly Canada and Australia. The actors behind climate change denial form a well-funded and relatively coordinated coalition of fossil fuel companies, industry groups, conservative think tanks, and contrarian scientists. [317] Like the tobacco industry before, the main strategy of these groups has been to manufacture doubt about scientific data and results. [318] Many who deny, dismiss, or hold unwarranted doubt about the scientific consensus on anthropogenic climate change are labelled as "climate change skeptics", which several scientists have noted is a misnomer. [319]

There are different variants of climate denial: some deny that warming takes place at all, some acknowledge warming but attribute it to natural influences, and some minimise the negative impacts of climate change. [320] Manufacturing uncertainty about the science later developed into a manufacturing controversy: creating the belief that there is significant uncertainty about climate change within the scientific community in order to delay policy changes. [321] Strategies to promote these ideas include criticism of scientific institutions, [322] and questioning the motives of individual scientists. [320] An echo chamber of climate-denying blogs and media has further fomented misunderstanding of climate change. [323]

Protest and litigation

Climate protests have risen in popularity in the 2010s in such forms as public demonstrations, [324] fossil fuel divestment, and lawsuits. [325] Prominent recent demonstrations include the school strike for climate, and civil disobedience. In the school strike, youth across the globe have protested by skipping school, inspired by Swedish teenager Greta Thunberg. [326] Mass civil disobedience actions by groups like Extinction Rebellion have protested by causing disruption. [327] Litigation is increasingly used as a tool to strengthen climate action, with many lawsuits targeting governments to demand that they take ambitious action or enforce existing laws regarding climate change. [328] Lawsuits against fossil-fuel companies, from activists, shareholders and investors, generally seek compensation for loss and damage. [329]

To explain why Earth's temperature was higher than expected considering only incoming solar radiation, Joseph Fourier proposed the existence of a greenhouse effect. Solar energy reaches the surface as the atmosphere is transparent to solar radiation. The warmed surface emits infrared radiation, but the atmosphere is relatively opaque to infrared and slows the emission of energy, warming the planet. [330] Starting in 1859, [331] John Tyndall established that nitrogen and oxygen (99% of dry air) are transparent to infrared, but water vapour and traces of some gases (significantly methane and carbon dioxide) both absorb infrared and, when warmed, emit infrared radiation. Changing concentrations of these gases could have caused "all the mutations of climate which the researches of geologists reveal" including ice ages. [332]

Svante Arrhenius noted that water vapour in air continuously varied, but carbon dioxide ( CO
2 ) was determined by long term geological processes. At the end of an ice age, warming from increased CO
2 would increase the amount of water vapour, amplifying its effect in a feedback process. In 1896, he published the first climate model of its kind, showing that halving of CO
2 could have produced the drop in temperature initiating the ice age. Arrhenius calculated the temperature increase expected from doubling CO
2 to be around 5–6 °C (9.0–10.8 °F). [333] Other scientists were initially sceptical and believed the greenhouse effect to be saturated so that adding more CO
2 would make no difference. They thought climate would be self-regulating. [334] From 1938 Guy Stewart Callendar published evidence that climate was warming and CO
2 levels increasing, [335] but his calculations met the same objections. [334]

In the 1950s, Gilbert Plass created a detailed computer model that included different atmospheric layers and the infrared spectrum and found that increasing CO
2 levels would cause warming. In the same decade Hans Suess found evidence CO
2 levels had been rising, Roger Revelle showed the oceans would not absorb the increase, and together they helped Charles Keeling to begin a record of continued increase, the Keeling Curve. [334] Scientists alerted the public, [336] and the dangers were highlighted at James Hansen's 1988 Congressional testimony. [21] The Intergovernmental Panel on Climate Change, set up in 1988 to provide formal advice to the world's governments, spurred interdisciplinary research. [337]


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Keystone Species

Every ecosystem has certain species that are critical to the survival of the other species in the system. The keystone species could be a huge predator or an unassuming plant, but without them the ecosystem may not survive.

Beaver

The American Beaver (Castor canadensis) is one example of a keystone species in North America.

Photograph by Michael Quinton / Minden Pictures

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In any arrangement or community, the &ldquokeystone&rdquo is considered one of the most vital parts. In a marine ecosystem, or any type of ecosystem, a keystone species is an organism that helps hold the system together. Without its keystone species, ecosystems would look very different. Some ecosystems might not be able to adapt to environmental changes if their keystone species disappeared. That could spell the end of the ecosystem, or it could allow an invasive species to take over and dramatically shift the ecosystem in a new direction.

Since a keystone species is not a formal designation, scientists may debate which plants or animals in a particular ecosystem deserve the title. Some wildlife scientists say the concept oversimplifies one animal or plant&rsquos role in complex food webs and habitats. On the other hand, calling a particular plant or animal in an ecosystem a keystone species is a way to help the public understand just how important one species can be to the survival of many others.

There are three types of keystone species cited by many scientists: predators, ecosystem engineers, and mutualists.

Predators help control the populations of prey species, which in turn affects the quantity of plants and animals further along the food web. Sharks, for example, often prey upon old or sick fish, leaving healthier animals to flourish. Simply by their presence near sea grass beds, sharks are able to keep smaller animals from overgrazing and wiping out the grass. Scientists in Australia observed that when tiger sharks were not near the grass beds, sea turtles&mdashamong tiger sharks&rsquo favorite prey&mdashtended to decimate them. But when tiger sharks patrolled the grass beds, the sea turtles were forced to graze across a much wider region.

Ecosystem Engineers

An ecosystem engineer is an organism that creates, changes, or destroys a habitat. There is perhaps no clearer example of a keystone engineer than the beaver. River ecosystems rely on beavers to take down old or dead trees along riverbanks to use for their dams. This allows new, healthier trees to grow in abundance. The dams divert water in rivers, creating wetlands that allow a variety of animals and plants to thrive.

When two or more species in an ecosystem interact for each other&rsquos benefit, they are called mutualists. Bees are a primary example of this. As bees take the nectar from flowers, they collect pollen and spread it from one flower to the next, enhancing the odds of fertilization and greater flower growth. Nectar and pollen are also the primary food sources for the bees themselves.

Some scientists identify other categories of keystone species. One alternate list includes predators, herbivores, and mutualists. Another cites predators, mutualists, and competitors for resources.

Keystone species can also be plants. Mangrove trees, for instance, serve a keystone role in many coastlines by firming up shorelines and reducing erosion. They also provide a safe haven and feeding area for small fish among their roots, which reach down through the shallow water.

In many cases, the vital role of a keystone species in an ecosystem is not fully appreciated until that species is gone. Ecologist Robert Paine, who coined the term &ldquokeystone species&rdquo in the 1960s, observed the importance of such species in a study of starfish along the rocky Pacific coastline in Washington state. The starfish fed on mussels, which kept the mussel population in check and allowed many other species to thrive. When the starfish were removed from the area as part of an experiment, the mussel population swelled and crowded out other species. The biodiversity of the ecosystem was drastically reduced. Payne&rsquos study showed that identifying and protecting keystone species can help preserve the population of many other species.

The American Beaver (Castor canadensis) is one example of a keystone species in North America.


Contents

The concept of the keystone species was introduced in 1969 by the zoologist Robert T. Paine. [1] [2] Paine developed the concept to explain his observations and experiments on the relationships between marine invertebrates of the intertidal zone (between the high and low tide lines), including starfish and mussels. He removed the starfish from an area, and documented the effects on the ecosystem. [3] In his 1966 paper, Food Web Complexity and Species Diversity, Paine had described such a system in Makah Bay in Washington. [4] In his 1969 paper, Paine proposed the keystone species concept, using Pisaster ochraceus, a species of starfish generally known as ochre starfish, and Mytilus californianus, a species of mussel, as a primary example. [1] The ochre starfish is a generalist predator and feeds on chitons, limpets, snails, barnacles, echinoids and even decapod crustacea. The favourite food for these starfish is the mussel which is a dominant competitor for the space on the rocks. The ochre starfish keeps the population numbers of the mussels in check along with the other preys allowing the other seaweeds, sponges and anemones to co-exist that ochre starfish do not consume. When Paine removed the ochre starfish the mussels quickly outgrew the other species crowding them out. The concept became popular in conservation, and was deployed in a range of contexts and mobilized to engender support for conservation, especially where human activities had damaged ecosystems, such as by removing keystone predators. [5] [6]

A keystone species was defined by Paine as a species that has a disproportionately large effect on its environment relative to its abundance. [7] It has been defined operationally by Davic in 2003 as "a strongly interacting species whose top-down effect on species diversity and competition is large relative to its biomass dominance within a functional group." [8]

A classic keystone species is a predator that prevents a particular herbivorous species from eliminating dominant plant species. If prey numbers are low, keystone predators can be even less abundant and still be effective. Yet without the predators, the herbivorous prey would explode in numbers, wipe out the dominant plants, and dramatically alter the character of the ecosystem. The exact scenario changes in each example, but the central idea remains that through a chain of interactions, a non-abundant species has an outsized impact on ecosystem functions. For example, the herbivorous weevil Euhrychiopsis lecontei is thought to have keystone effects on aquatic plant diversity by foraging on nuisance Eurasian watermilfoil in North American waters. [9] Similarly, the wasp species Agelaia vicina has been labeled a keystone species for its unparalleled nest size, colony size, and high rate of brood production. The diversity of its prey and the quantity necessary to sustain its high rate of growth have a direct impact on other species around it. [7]

The keystone concept is defined by its ecological effects, and these in turn make it important for conservation. In this it overlaps with several other species conservation concepts such as flagship species, indicator species, and umbrella species. For example, the jaguar is a charismatic big cat which meets all of these definitions: [10]

The jaguar is an umbrella species, flagship species, and wilderness quality indicator. It promotes the goals of carnivore recovery, protecting and restoring connectivity through Madrean woodland and riparian areas, and protecting and restoring riparian areas. . A reserve system that protects jaguars is an umbrella for many other species. . the jaguar [is] a keystone in subtropical and tropical America .


Generalist and Specialist Species

Generalist species can feed on a wide variety of things and thrive in various environments. Specialist species eat a limited diet and occupy a much narrower niche.

Clinging to Mom

Koala are a specialist species, only feeding on the leaves of the eucalyptus tree.

Photograph by Anne B. Keiser

In the field of ecology, classifying a species as a generalist or a specialist is a way to identify what kinds of food and habitat resources it relies on to survive. Generalists can eat a variety of foods and thrive in a range of habitats. Specialists, on the other hand, have a limited diet and stricter habitat requirements.

Raccoons (Procyon lotor) are an example of a generalist species. They can live in a wide variety of environments, including forests, mountains, and large cities, which they do throughout North America. Raccoons are omnivores and can feast on everything from fruit and nuts to insects, frogs, eggs, and human trash. Other examples of generalist species include bobcats and coyotes.

An example of a specialist species is the koala (Phascolarctos cinereus). Native to Australia, koalas are herbivorous marsupials that feed only on the leaves of the eucalyptus tree. Therefore, their range is restricted to habitats that support eucalyptus trees. Within this diet, some koalas specialize even further and eat leaves from only one or two specific trees.

An example of a carnivorous specialist is the Canada lynx (Lynx canadensis), which preys upon snowshoe hare. Canada lynx (Lepus americanus) inhabit the forested, mountainous areas favored by their prey, and are well-adapted to hunting in deep, soft snow.

Like the koala and the Canada lynx, specialist species evolved to fit a very specific niche. This can pose a problem when environmental disruptions, like effects from climate change or habitat loss, occur. Such disturbances have a strong effect on specialists because they cannot adapt to use other food sources or habitats as quickly as generalist species. In fact, some scientists have found that the number of specialist species is declining due to human activity, and the number of generalist species is on the rise.

Koala are a specialist species, only feeding on the leaves of the eucalyptus tree.


Watch the video: Πώς ξεραίνουμε ανεπιθύμητα δέντρα ή θάμνους. (June 2022).


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