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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

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Can animals and plants adapt to global warming?

What the science says...

Human-caused climate change is occurring too rapidly for species to be able to adapt. Plants and animals are currently dying off at a rate that is 100 to 1000 times faster than the average rate of extinction over geological timescales. Because of this, there is mounting evidence that we are heading towards a mass extinction event.

Climate Myth...

Animals and plants can adapt

[C]orals, trees, birds, mammals, and butterflies are adapting well to the routine reality of changing climate." (source: Hudson Institute)

There have been five “big” mass extinction events in Earth’s history, each one driven by rapid climatic change. When climate changes too fast for species to be able to adapt, extinctions are bound to occur. Figure 1 shows prior extinction events and atmospheric CO2 concentration over geological time. Each open circle denotes an extinction event (big or small), with the “Big Five” mass extinctions highlighted. Note that nearly every extinction event occurred after a sharp increase in CO2 levels, including four out of the Big Five.

The only one of the Big Five mass extinctions where this did not occur is the most recent Paleocene Thermal Extinction, that wiped out the dinosaurs 65 million years ago. This was kicked off by a large meteor strike (a different, more jarring change in climate). Most extinctions have been linked to immense volcanic events, called Large Igneous Province (LIP) eruptions. These events spew billions of metric tonnes of carbon dioxide (CO2) and sulfur dioxide (SO2) into the atmosphere, in many cases triggering marine anoxia (oxygen loss) and ocean acidification due to rapid greenhouse warming. 

The largest of the mass extinctions, the Permian Extinction (also known as the “Great Dying), resulted in the loss of nearly 96% of all marine species and 70% of all terrestrial species at the end of the Permian Era 251 million years ago. During this event, which was triggered by an LIP eruption in modern-day Siberia, global temperatures warmed by nearly 10 °C and the world’s oceans lost up to 80% of their oxygen content. This eruption, which lasted over a period of approximately 900,000 ± 800,000 years, is estimated to have released as much as 170,000 gigatonnes (Gt) of CO2 into the atmosphere. Using these estimated values, one can compute that CO2 was released at an average rate of about 0.1 to 1.7 Gt/year during the event. This is much less than the rate at which humans are emitting CO2 today. For example, we released 33 Gt CO2 in the year 2019 alone, and current projections show that global emissions are only going to increase in the near future. 

One myth argues that this change is fine, because animals and plants have adapted to shifts in CO2 concentration or temperature of similar magnitude. For example, Earth has had periods in the past where CO2 concentrations reached levels of 1-2 thousand parts per million, much higher than today. Also, the global average temperature difference between ice ages and the warm interglacial periods between them is thought to be nearly 4-7 °C. These natural changes may seem drastic, however, the rates of global mean change associated with them are not comparable to the changes we are experiencing today or at the onset of each mass extinction event.

When contrarians argue that species will be able to adapt to current climate change because they have adapted to “routine” climate changes in the past, they are committing the fallacy of false equivalence. We cannot compare how species adapted to natural climate shifts (like ice age cycles) to how they will adapt to future, human-caused change because they take place over different timescales. Comparing rapid, human-caused climate change to the slow, natural climate change of the past is like comparing apples to oranges.

Most large, natural shifts in CO2 concentration have occurred over tens to hundreds of thousands of years (Figure 2). For example, the periods between ice ages and warm periods occur over about 10,000 years, with a warming rate of about 0.005 °C/decade. Comparatively, state-of-the-art climate models predict that global mean temperatures will warm by 2-6 °C in the next 100 years due to anthropogenic climate change. This current rate of warming would be 20-60 times faster than the natural warming rate after ice ages. Today’s shifts in CO2 concentration and global mean temperature due to human emissions are occurring too fast for plants and animals to be able to adapt.  

Future climate change aside, the natural world has already been under attack for centuries. Since the discovery of agriculture, humans have massively transformed the globe through the expansion of modern civilization, to the detriment of Earth’s biodiversity. More recently, this transformation was kicked into high gear with the Industrial Revolution of the late 1800s. Great swathes of temperate forest in Europe, Asia and North America have been cleared over the past few centuries for agriculture, timber, and urban development. Tropical forests in South America and Africa are now on the front line. Human-assisted species invasions of pests, competitors, and predators are rising exponentially, and overexploitation of fisheries and forest animals for meat have already driven many species to the point of collapse.

The ways plants and animals adapt to changes in their environment have also been severely hampered. In order for many species to migrate large distances – one of the main ways animals adapt to climatic shifts – they would have to cross large areas of human influence. Mass migration in areas of large human population – entwined with crisscrossing, high-speed highways and polluted, dammed-up rivers – is a challenging task. Along with this, it has been shown that climate change has already had an impact on the environmental cues that animals use to determine the timing and navigation of their migratory patterns. Subsequently, these changes in animal migratory behavior have also been shown to have a detrimental effect on the an animal’s average lifespan and overall health.

There is much evidence that we are already on the brink of a sixth mass extinction event. Because of human activity, the number of species on the planet is already decreasing. According to the Millennium Ecosystem Assessment (an international environmental report with the goal of assessing the impact of ecosystem change on human well-being), 60% of the world’s ecosystems are now degraded and the global rate of extinction is already at 100 to 1000 times that of the “normal” background rate on geological timescales. Because mass extinction events take place over a long time period compared to human life spans, this evidence alone is not enough to definitely conclude the occurrence of such an event. However, we can say with certainty that rapid, anthropogenic climate change will only make things worse for Earth’s biodiversity.

If we fail to prevent catastrophic climate change, there will be many regions of the world (some of which are highly populated) which will become uninhabitable to even us humans. This is based on human physiology and future temperature and humidity predictions under climate change. When temperature and humidity levels are too high – indicated by something scientists call a high “wet bulb temperature” – the human body is not able to cool itself by sweating. Extended periods of these high wet bulb temperatures increase the rate of heat stroke and death in humans. Here in the U.S., large areas of the Mississippi Valley, the South, and Arizona could have almost a month’s worth or more of these dangerously hot and humid days by the year 2050 (Figure 3). When we zoom out to the entire globe, it gets worse, specifically in tropical regions. Right now, only 1% of the Earth’s land is considered a “barely livable” hot zone, mainly within the Sahara and other deserted regions. If emissions continue unregulated and climate change continues unmitigated, this fraction could increase to 19% by 2070. Billions of people live in these potential, future hot zones. Due to the current state of the global economy, many disadvantaged people residing in these potentially deadly places may not be able to move away or adapt.

In summary, the current outlook on Earth’s biodiversity is gloomy. We know that most mass extinctions in the fossil record have been triggered by the rapid onset of global warming due to an increase in carbon dioxide emissions to the atmosphere. In the past, these emissions were usually due to large, volcanic episodes which occurred over tens to hundreds of thousands of years. On a geological timescale, these changes occurred in the blink of an eye, and this is why they were so costly. The human-caused climate change that is occurring today is similar; since 1850, we have increased atmospheric CO2 levels to the highest they have been in the last 3 to 5 million years. Humans are changing the Earth’s climate faster than animals and plants are able to adapt, and a multitude of evidence points to the occurrence of a sixth mass extinction. Even though this may be depressing, there is still hope. There is still time to reverse the worst effects of man-made climate change, and to do so we must support conservationist efforts and transition to renewable energy. For all of human history we have depended on Earth’s biodiversity, and it now depends on us to save it.

Last updated on 13 November 2020 by fhaychap. View Archives

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Further reading/viewing

Here are related lecture-videos from Denial101x - Making Sense of Climate Science Denial

Additional videos from the MOOC

State of the Wild, A Global Portrait of Wildlife, Wildlands, and Oceans by James Hansen

Comments

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Comments 51 to 63 out of 63:

  1. Re: Anthony's post about Candian geese, @50: Here in Colorado we refer to them as 'illegal residents.' They are also here now, year-round, and I clearly remember this not being the case 30+ years ago. No wonder: We feem them so well with our over-irrigated Kentucky blus grass lawns, and excessive non-native trees, coupled with the fact of shorter, warmer winters, they made the Adam Smith rational choice, and stayed over.

  2. Responding to tkman0 question asked here

    It's helpful if you provide sources to where you got your understanding to better understand the question. However, if you read the article above it should help. Ease of adaption depends on the rate of change. It takes time for suitable soils to develop for instance and the change is not merely about temperature but also changes in precepitation etc. Climate change does not affect hours of sunlight either.

  3. tkman0 asks elswhere:

    "I understand that plants might not necessarily migrate north as temperatures increase and as their climatic boundaries change, but why is that the case? If you could point me towards a page or two that explains it, it would be appreciated."

    Well, this page asserts it, but does not explain it.  Discussion is at least on topic here.  So:

    Tree ranges do in fact migrate with temperatures.  This has been well established from evidence of response to the warming at the end of the last glacial using data from pollen and other plant remains:

    It is also evident in Europe, where there are a large number of species confined to one or a few mountains, the result of gradual migration up the mountain slope as the Earth warmed with the consequent genetic isolation allowing the evolution of new species.

    Migration in response to AGW faces three major limitations.

    First, migration may simply be not physically possible.  The alpine species mentioned above, for example, have an obvious limit to their migration with increasing warming such that any whose lower altitude range is within 600 meters of the summit will go extinct with a regional temperature rise of 4 C.  Indeed, they may go extinct with a smaller temperature rise in that as the population approaches the summit, a smaller and smaller population can be supported leaving them vulnerable to extinction by chance fluctuations on population due to disease, predation or unusual weather.  Similar issues face species near northern coastlines (in the NH).  A regional rise in temperature of 4 C will do for (at least locally) most species whose southern limit is within 600 km of a northern coastline:

     

    In addition to these obvious bariers, east-west mountain ranges, or even large scale changes in underlying soil type can present natural bariers to migration, and hence potential exinction threats.

    More importantly in the modern world is that human activity has created a very large number of additional bariers to migration (the second limitation).  Put simply, seeds from trees that land in cornfields do not grow to maturity.  Nor, come to that, do they typically grow to maturity in pasturage.  The vast farmlands developed by humans across the NH represent a major barier to the migration of the range of trees.

    Finally, and most importantly, the third barrier is the simple pace of temperature change.  We are currently facing an increase of temperature of about 3 C over the coming century.  That equates to a distance of about 450 km of change in latitudinal range to preserve current species health.  Trees that propogate by dropping  seeds can change there range at a few hundred meters per generation at most.  (They can do so much faster if the seeds are dispersed by birds, and to a lesser extent winds.)  Given the pace at which climate is changing, they well simply be left behind.  

    The effect will be complicated.  Intuitively that means their northern range will not expand as rapidly as their southern range retreats - but that is not necessarilly true.  For trees, like most life forms, the greatest competition comes from other species rather than from the environment itself.  This is shown by the shere range of environments in which trees protected from competition by being in gardens can grow.  It follows that the southern range will only retreat rapidly if some competitor species can advance quickly.  So the actual likely result (IMO) is that long lived, slow growing species will be displaced by short lived quick growing species across the range.  

  4. Thanks for the replies everyone, also just wanted to point out that some of the links on here dont link to articles, but insteasd link simply to a general climate change page at the univeristy of texas.

  5. tkman0

    The latest IPCC report has this graph about species movement rates vs warming rates

  6. There was an interesting find I saw published in the journal of Nature Communications published September 2014:Central Europe Tree Growth


    ...we show that, currently, the dominant tree species Norway spruce and European beech exhibit significantly faster tree growth (+32 to 77%), stand volume growth (+10 to 30%) and standing stock accumulation (+6 to 7%) than in 1960.

     

    That's interesting, a 75% increase in growth rate in beech trees in parts of Europe.

    My personal inclination is simply to work to manage forests responsibly.

  7. Protagorias,

    I saw an interesting find where it described that 25% of the trees in Texas over 4" diameter at breast height were killed by the drought they have had.   In California the current drought is the worst in the past 1200 or more years.  Fires alone have killed millions of trees.  Do you think the increase in trees in Central Europe is more or less than the decrease in trees in the American West?  What should we do to manage the forests more responsibly in the face of historic droughts?   

  8. Looking deeper I found this reference which is more reliable and suggests only about 5% of Texas trees were killed by the 2011 drought.  I stand by my point that managing forrests will produce little return in the face of historic drought.

  9. michael sweet,

    Climate change is undoubtedly happening at a very rapid and uncomfortable pace. And droughts are obviously a big concern.

    Perhaps what can produce a lot of return in the long run, be economocially sound jobs, as well as potentially help in managing forests and mitigating drought, is to gain the technology to unlock some of the water locked up the ringwoodite inside our planet. I think there's something like two or three times the volume of the world's oceans locked up in ringwoodite, but it's around 500 miles down.

  10. Once desertification takes hold it is an irreversible process. That is not to say the rain won't fall elsewhere yet where and in what proportion?

    The concept of non-linearity means there are no promises!

    Who can tell me if the economic rise of China has yet been reflected in the Keeling curve, for instance?

  11. To Anthony @50: Don't know much about birds but mentioning "migration" reminded me of a doco I saw the other night(about "song-birds" I think!?!) that said birds in the Northern hemisphere and the Southern hemisphere act differently. I think there may be a climatic reason to it but I can't remember what it was!

  12. This is appeal to nature fallacy. Just because some species exist, doesnt mean it's necessarily good that they continue to exist. Also, "animals/plants can adapt" doesnt necessarily mean every specie will adapt. it means life in general will adapt and create new forms of animals who, guess what, can now survive in the new climate. Throughout history catastrophic events changed entire climate of the planet in a day. and yet life survived, and flourished. So this entire appeal to nature fallacy is wholly uninteresting to me.

  13. guad,

     You are factually incorrect. An appeal to nature is an argument or rhetorical tactic in which it is proposed that "a thing is good because it is 'natural', or bad because it is 'unnatural'".

    Whereas this article focuses on actual things that are bad...because they would be bad whether natural or not. Ecosystems have functions. We call this ecosystem services. You might want to read up on it, since it is what keeps you alive. Ecosystem services

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