Will global warming cause a mass extinction event?

Originally posted on Skeptical Science… A related post can be found here.

Southeast Asian extinctions projected due to habitat loss (source: Sodhi, N. S., Koh, L. P., Brook, B. W. & Ng, P. K. L. 2004)

Human are transforming the global environmental. 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 are now on the front line. Human-assisted species invasions of pests, competitors and predators are rising exponentially, and over-exploitation of fisheries, and forest animals for bush meat, to the point of collapse, continues to be the rule rather than the exception.

Driving this has been a six-fold expansion of the human population since 1800 and a 50-fold increase in the size of the global economy. The great modern human enterprise was built on exploitation of the natural environment. Today, up to 83% of the Earth’s land area is under direct human influence and we entirely dominate 36% of the bioproductive surface. Up to half the world’s freshwater runoff is now captured for human use. More nitrogen is now converted into reactive forms by industry than all by all the planet’s natural processes and our industrial and agricultural processes are causing a continual build-up of long-lived greenhouse gases to levels unprecedented in at least the last 800,000 years and possibly much longer.

Clearly, this planet-wide domination by human society will have implications for biological diversity. Indeed, a recent review on the topic, the 2005 Millennium Ecosystem Assessment report (an environmental report of similar scale to the Intergovernmental Panel on Climate Change Assessment Reports), drew some bleak conclusions – 60% of the world’s ecosystems are now degraded and the extinction rate is now 100 to 1000 times higher than the “background” rate of long spans of geological time. For instance, a study I conducted in 2003 showed that up to 42% of species in the Southeast Asian region could be consigned to extinction by the year 2100 due to deforestation and habitat fragmentation alone.

Given these existing pressures and upheavals, it is a reasonable question to ask whether global warming will make any further meaningful contribution to this mess. Some, such as the sceptics S. Fred Singer and Dennis Avery, see no danger at all, maintaining that a warmer planet will be beneficial for mankind and other species on the planet and that “corals, trees, birds, mammals, and butterflies are adapting well to the routine reality of changing climate”. Also, although climate change is a concern for conservation biologists, it is not the focus for most researchers (at present), largely I think because of the severity and immediacy of the damage caused by other threats.

Global warming to date has certainly affected species’ geographical distributional ranges and the timing of breeding, migration, flowering, and so on. But extrapolating these observed impacts to predictions of future extinction risk is challenging. The most well known study to date, by a team from the UK, estimated that 18 and 35% of plant and animal species will be committed to extinction by 2050 due to climate change. This study, which used a simple approach of estimating changes in species geographical ranges after fitting to current bioclimatic conditions, caused a flurry of debate. Some argued that it was overly optimistic or too uncertain because it left out most ecological detail, while others said it was possibly overly pessimistic, based on what we know from species responses and apparent resilience to previous climate change in the fossil record – see below.

A large number of ancient mass extinction events have indeed been strongly linked to global climate change, including the most sweeping die-off that ended the Palaeozoic Era, 250 million years ago and the somewhat less cataclysmic, but still damaging, Palaeocene–Eocene Thermal Maximum, 55 million years ago. Yet in the more recent past, during the Quaternary glacial cycles spanning the last million years, there were apparently few climate-related extinctions. This curious paradox of few ice age extinctions even has a name – it is called ‘the Quaternary Conundrum’.

Over that time, the globally averaged temperature difference between the depth of an ice age and a warm interglacial period was 4 to 6°C – comparable to that predicted for the coming century due to anthropogenic global warming under the fossil-fuel-intensive, business-as-usual scenario. Most species appear to have persisted across these multiple glacial–interglacial cycles. This can be inferred from the fossil record, and from genetic evidence in modern species. In Europe and North America, populations shifted ranges southwards as the great northern hemisphere ice sheets advanced, and reinvaded northern realms when the glaciers retreated. Some species may have also persisted in locally favourable regions that were otherwise isolated within the tundra and ice-strewn landscapes. In Australia, a recently discovered cave site has shown that large-bodied mammals (‘megafauna’) were able to persist even in the arid landscape of the Nullarbor in conditions similar to now.

However, although the geological record is essential for understanding how species respond to natural climate change, there are a number of reasons why future impacts on biodiversity will be particularly severe:

A) Human-induced warming is already rapid and is expected to further accelerate. The IPCC storyline scenarios such as A1FI and A2 imply a rate of warming of 0.2 to 0.6°C per decade. By comparison, the average change from 15 to 7 thousand years ago was ~0.005°C per decade, although this was occasionally punctuated by short-lived (and possibly regional-scale) abrupt climatic jolts, such as the Younger Dryas, Dansgaard-Oeschger and Heinrich events.

B) A low-range optimistic estimate of 2°C of 21st century warming will shift the Earth’s global mean surface temperature into conditions which have not existed since the middle Pliocene, 3 million years ago. More than 4°C of atmospheric heating will take the planet’s climate back, within a century, to the largely ice-free world that existed prior to about 35 million years ago. The average ‘species’ lifetime’ is only 1 to 3 million years. So it is quite possible that in the comparative geological instant of a century, planetary conditions will be transformed to a state unlike anything that most of the world’s modern species have encountered.

C) As noted above, it is critical to understand that ecosystems in the 21st century start from an already massively ‘shifted baseline’ and so have lost resilience. Most habitats are already degraded and their populations depleted, to a lesser or greater extent, by past human activities. For millennia our impacts have been localised although often severe, but during the last few centuries we have unleashed physical and biological transformations on a global scale. In this context, synergies (positive or self-reinforcing feedbacks) from global warming, ocean acidification, habitat loss, habitat fragmentation, invasive species, chemical pollution (Figure 2) are likely lead to cascading extinctions. For instance, over-harvest, habitat loss and changed fire regimes will likely enhance the direct impacts of climate change and make it difficult for species to move to undamaged areas or to maintain a ‘buffer’ population size. One threat reinforces the other, or multiple impacts play off on each other, which makes the overall impact far greater than if each individual threats occurred in isolation (Brook et al 2008).

Figure from the Millennium Ecosystem Assessment

D) Past adaptation to climate change by species was mainly through shifting their geographic range to higher or lower latitudes (depending on whether the climate was warming or cooling), or up and down mountain slopes. There were also evolutionary responses – individuals that were most tolerant to new conditions survived and so made future generations more intrinsically resilient. Now, because of points A to C described above, this type of adaptation will, in most cases, simple not be possible or will be inadequate to cope. Global change is simply too pervasive and occurring too rapidly. Time’s up and there is nowhere for species to run or hide.

For references and reprint requests, visit: http://www.adelaide.edu.au/directory/barry.brook

Some key recent scientific papers by the author on this topic:

Brook, B.W., Sodhi, N.S. & Bradshaw, C.J.A. (2008) Synergies among extinction drivers under global change. Trends in Ecology & Evolution, 23, 453-460. http://dx.doi.org/10.1016/j.tree.2008.03.011

Brook, B.W. (2008) Synergies between climate change, extinctions and invasive vertebrates. Wildlife Research, 35, 249-252. http://dx.doi.org/10.1071/wr07116

Bradshaw, C.J.A., Sodhi, N.S. & Brook, B.W. (2008). Tropical turmoil – a biodiversity tragedy in progress. Frontiers in Ecology & Environment, http://dx.doi.org/10.1890/070193

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50 Comments

  1. Pingback: Global warming and biodiversity extinction « ConservationBytes.com

  2. Academics like yourself, by whipping the world into a mindless frenzy about AGW will certainly cause environmental problems by misdirecting resources that should be applied to solve these real problems.
    While good economies don’t guarantee good ecology and ethics, poor economies certainly guarantee bad outcomes.

  3. Drongo: If you read the above you’ll note that I don’t think the other problems are unimportant – indeed, if you look at my bio, you’ll find that I’ve spend a considerable fraction of my research career studying these issues. My point is that climate change is a concern beyond the problem that it will just add to other threatening processes. It seems increasingly likely that it will worsen them. Here is the abstract of my Trends in Ecology and Evolution article, which makes that a little plainer:

    If habitat destruction or overexploitation of populations is severe, species loss can occur directly and abruptly. Yet the final descent to extinction is often driven by synergistic processes (amplifying feedbacks) that can be disconnected from the original cause of decline. We review recent observational, experimental and meta-analytic work which together show that owing to interacting and self-reinforcing processes, estimates of extinction risk for most species are more severe than previously recognised. As such, conservation actions which only target single-threat drivers risk being inadequate because of the cascading effects caused by unmanaged synergies. Future work should focus on how climate change will interact with and accelerate ongoing threats to biodiversity, such as habitat degradation, overexploitation and invasive species.

  4. Louis, the Pleistocene is one of the Epochs of the Quaternary Period, which I discuss above when I’m talking about the Quaternary paradox. The Pleistocene extinctions is one of my areas of research interest (see my publication list) – the balance of evidence suggests the megafauna on each continent was primarily driven extinct by human hunting, with the only strong overlap with a major climatic event occurring in North America.

  5. It seems to me that we are already experiencing a mass extinction event, sometimes known as the holocene extinction event. This appears to have been accelerating over the past century or so. The question to me seems to be mow much worse will climate change cause it to be?

    One issue is that, as mentioned in (C) above, habitat destruction combines with climate change impacts to make species extinctions more of a problem. This suggests to me that activities that protect and restore habitat have an important adaptation impact, by mitigating species loss. They also have a mitigation impact, by sequestering carbon.

    Another issue is that climate change means that the Earth will enter a new geological era.

  6. Barry,
    From my ignorant observations of nature I find that 0.5 degrees cooling has a much more overwhelming effect on flora and fauna than the reverse and I’ve watched the same things die at -5c and at 50c.
    There will always be lots of room in between for survival so don’t panic about temperatures.
    The extinction of say, koalas, has been happening for some time and is nearly complete.
    Got nothing to do with AGW, just political crap that no one wants to confront.
    Want to do something useful? Address that.

  7. Since we are COOLING and there is no prospect of global warming it is a stupid question. But a new “little ice age” will hurt land-based species much worse than warming. And particularly higher CO2 levels are good for the prospects of pretty much every species there is.

  8. Spangled Drongo.

    I have to accede to your self-confessed ‘ignorant observations’, thus I will certainly not presume to contradict you.

    And so, to help spark the enlightenment of your dark mine of ignorance just a little bit, I suggest that you consider what a small increment in average global temperature means for the koala’s cousin, the mountain pygmy possum.

    Once you have educated yourself you could branch out from this one small taxon, and seriously investigate a whole world of species diversity.

    If you bother to do so, you will soon be confronted with the sheer embarrassing magnititude of your former ignorance.

  9. I’ve listened to your first seminar already. But the fact is we are cooling. And there is no prospect for warming. And in a cooling environment extra CO2 would be helpful for the robustness of the natural world.

  10. Barry,
    If you are genuinely concerned about mass extinctions, what about trying to convince academics and politicians that the dingo is not a native animal.
    Proving that it wasn’t [which seems straight forward but not easy] would hopefully lead to its eradication from national parks and along with it, dogs and foxes.
    This is one simple hurdle that is responsible for massive deaths and almost certainly local extinctions of ground dwelling native wildlife.
    Maybe you know of an aspiring PhD who is looking for a thesis and then take it further.

  11. Graeme Bird

    If you really did listen to Prof Brook’s fist seminar (I am not convinced you did) and followed the accompanying Power Point presentation, and you still believe the world is cooling you must either have had cotton wool in your ears at the time as your eyes shut, or have been totally unable to follow the clear, well-explained logical science. “There are none so blind as those who will not see” John Heywood PROVERBS (1546)

  12. CJA Bradshaw,
    Thanks for that. I think it is difficult to be specific about whether dingoes control foxes and cats.
    I see areas where they cohabit happily but some areas like Fraser Is. don’t seem to have many foxes and cats or any other ground dwelling wildlife for that matter.
    If dingoes were treated as ferals it would allow baiting in national parks and dogs, dingoes and foxes could be eradicated.
    While this isn’t being done, these large areas of environmental significance are simply becoming nurseries for feral predators at the huge expense of our native ground dwellers.

  13. The real problem is the cat – dingoes suppress cat density, and there’s really very little chance of controlling cat numbers in any meaningful way at the continental scale. See Tony Peacock’s blog on just how bad cats really are – certainly the most devastating feral species (humans apart) to have reached Australian soil. And cats are nearly ubiquitous in Australia (apart from a few islands such as Macquarie where they’ve been recently eradicated; then again, there are no dingoes or foxes there either). Some islands might be a special case, but on the whole, we’re better off with dingoes than without.

    CJA Bradshaw

  14. You would need a big population of dingoes permanently in an area to reduce foxes and cats and I’m sure this happens in areas like Fraser Is but in the channel country eg you can have big populations of dingoes as well as cats. I’ve had 100 dogs yodelling around me and cats in the coolibahs.
    In steep mountainous country you can have dingoes living close to foxes and cats but not usually in such large numbers.
    Foxes and cats can live in areas inaccessible to dingoes. Cats in trees. Foxes in rock holes on cliff faces etc.
    My experience with all these predators is that they are mainly happy to tolerate one another and concentrate on their prey.
    What happens when a cat and dog fight?
    They both get ripped about a bit and end up with mutual respect for each other.

  15. I agree that cats are bad and I petitioned every one I could over savannah cats.
    The only thing that kills cats is scrub ticks and areas that still have scrub ticks have some chance.
    Except from domestic cats. They get a dose of ticks then go home and get “frontlined” and are back in action the following night.

  16. CJA,
    If you think, “we’re better off with dingoes than without”, have a butcher’s hook at Fraser Is.
    The wildlife list is derived from the bones found in dingo faeces 30 years ago and apart from goannas there’s little else.
    Don’t leave your kids lying around either.
    This island 30 years ago was resumed as a national park because it had the capacity to become a refuge for endangered native wildlife.
    Look at it now. A dingo theme park and no wildlife in sight.
    Similar Islands over run with industry, residential and feral cats leave it for dead for biodiversity.
    So much for the dingo!

  17. What happens when a cat and dog fight?
    They both get ripped about a bit and end up with mutual respect for each other.

    Well, here in the US coyotes won’t tolerate cats, and simply kill them (urban coyotes are pretty common here in any area with reasonable amounts of greenspace). Wouldn’t surprise me at all if dingos do the same.

    The argument being made isn’t that dingos aren’t destructive of wildlife, but that on balance their role in controlling other predators makes their presence a plus.

  18. “The argument being made isn’t that dingos aren’t destructive of wildlife, but that on balance their role in controlling other predators makes their presence a plus.”

    What a good argument! Let’s just have dingoes in our national parks and nothing else.
    Like Fraser Is.

    Single dingoes are not capable of killing big feral cats. They are also not known for their fighting ability.
    Cats and foxes are more agile and smarter than a dingo and in the bush no self respecting cat or fox would ever confront a dingo.
    Cats and dingoes are both pack animals and are generally happy to live and let live like most carnivores.
    The main killer of feral cats in Australia is the scrub tick, not dingoes.

  19. What a good argument! Let’s just have dingoes in our national parks and nothing else.
    Like Fraser Is.

    So all of Australia’s National Parks are like Fraser Island? All alike? A one-fits-all conservation strategy is best?

    Strange, it hasn’t worked out that way in the US …

    Interestingly, a bit of googling seems to make it clear that your view that dingos don’t kill feral cats or introduced foxes isn’t … universally held … by experts.

  20. “So all of Australia’s National Parks are like Fraser Island? All alike? A one-fits-all conservation strategy is best?”

    Your long distance, lightweight logic as usual puts you in the problem pocket instead of the solution slot.

  21. Bernard J,
    I am still waiting for your posting on the coming mass extinction of the mountain pygmy possum due to AGW.
    One point you may need to consider: their most likely extinction due to feral cats could be posponed as AGW is reportedly spreading the scrub [paralysis] tick which will help control these cats.

  22. Lions are the only truly social (‘pack’) cats. All other cat species are basically solitary, though feral domestic cats can certainly form loose social groups near abundant food sources, etc.

  23. Even a modest amount of global warming might be enough to reduce the snow cover to such an extent that the survival of the mountain pygmy possum will be in jeopardy. Already threatened by the development of ski fields, bushfires and feral predators such as cats and foxes, the mountain pygmy possum is known to exist in only three genetically distinct populations, over an area of 10 square kilometres, in the NSW and Victorian Alps. Its ability to hibernate during winter is an important element of its survival; the energy it saves probably gives it a competitive advantage over non-hibernating species in areas with seasonal snow cover.

    However, with global warming, the extent of snow cover in Australia is predicted to decline dramatically. Even today it comprises only 0.15 per cent of the continent, an area that could decrease by 39 to 96 per cent by 2070. An average temperature rise of only 3ºC would entirely eliminate snow from all Australian mountains. Scientists predict that a loss of snow cover would increase winter mortality of the species, because of decreased insulation and a reduction in the availability of suitable habitat. Moreover, the breeding grounds of one of the possum’s most important food sources, the Bogong moth, could be affected by increased drought due to global warming. The net effect would almost certainly be an increase in the vulnerability of the mountain pygmy possum to extinction. Already there is evidence that annual snow cover is decreasing; for example, a strongly decreasing trend has been detected at the Spencers Creek snowfield between 1959 and 1999.

    Australian Academy of Science

    Spangled Drongo, that’s a lay summary from the AAS. It’s a brief summary only, and it omits important points such as the fact that not all snow cover needs to be lost to imperile the possum. Especially so given the pressure of ski-field use of their habitat in winter.

    Talking with some mammalogists it is considered that the warming that is already in train with current emissions may be sufficient to irreparably damage their hibernation grounds, and make no mistake, without their hibernation grounds the MPP is in deep trouble. Even only slightly reduced suitability of their hibernation ranges, when acting in concert with other pressures, put the possum in grave danger. For example, any change in summer fire regimes resulting from warming-induced climate change will also impact on the possum, even without loss of all winter snow.

    And please note that I did not state that a 0.5C increase would automatically wipe out the MPP. A sustained increase of this magnitude would make it very vulnerable though, and only a degree or two more would practically guarantee its non-viability in its natural habitat.

    On another note, I share no love for feral cats, and in fact a part of my work involves trapping and removing them from ecologically sensitive habitat. I certainly do not dispute the impact of cats on the MPP, and I never did. However, any climate-related increase in tick infestation is hardly likely to significantly alter cat impacts on native wildlife in southern areas of Australia for decades, and indeed the impact of cats on MPP only makes the possums’ vulnerability to warming even greater, ticks or not.

    I can tell you now, if it warms enough to allow ticks to wipe out cats in the Snowies, by that time they won’t have been the Snowy Mountains for many many years. And the MP possums would have long ceased to exist as a naturally-occurring/functioning species.

    Spangled Drongo, a 0.5C or slightly greater increase can spell doom for many species. My brother-in-law works on a salmon farm that is currently only a degree or so away from complete loss of stock with summer currents, and their scientists are investigating alternative species in preparation for the day when their salmon go belly up and stay that way.

    The orchardists in the same area are ripping out traditional varieties of fruit trees because they no longer receive the required hours of winter chilling to set any decent amount of fruit. The nothophagus forests that crown the remnants of the volcanic ranges along the east coast are only there because the cool alpine temperatures halt the march of eucalypts all the way uphill – but it wouldn’t take a great increase at all to tip the balance in favour of the gums and send them all the way to the top, wiping out whole nothophagus communities in the process.

    The bottom line in simple. If it warms even a couple of degrees, there will be profound ecological change, and loss of species. The bioclimatic envelopes of many species are that tight. You might not believe that there is warming, but the plants and animals that rely on the current climatic status quo don’t care a whit what you think. They’ll just go on with their business of integrating the parameters of the environments in which they live, and thus determine on their own, without computers or conspiracy theories, whether they survive or not.

    The trouble is, the signs are starting to emerge that for some it’s “or not”.

  24. Spangled Drongo.

    The feral cats that I have come across are most definitely not ‘pack’ animals. The adults usually only come together to mate, and the kittens bugger off as soon as they are able to look after themselves, especially the males.

    As WotWot noted above, around abundant sources of food (such as garbage tips and dumpster areas) cats will congregate in loose communities that tolerate each other rather than working as a functioning pack unit, but this is a largely artificial situation.

    Escaped domestics may have been conditioned to accept the company of other cats, but a true feral, in a non-urban environment, is not a tolerant beast.

    The scars and abscesses from fights that I’ve seen on the cats I’ve caught attest to that.

  25. Bernard J.
    Thanks for that. The mountain pygmy possum is not in my territory but it has obviously been around for a few interglacials and they and the holocene have had temperatures well in excess of present ones.
    Animals that survive warm summers can usually handle mild winters whereas feral cats would be a clear and present danger, I would imagine, for these animals. As certainly would dogs, dingoes and foxes.
    I would certainly agree with you that human population invasion such as ski fields and overburning would impact on these animals.
    Ticks BTW, were in the Aust Alps when Hume and Hovel walked to Port Phillip in 1824 [I seem to remember them being roundly cursed in their diaries] and if they are not there now helping the MPPs to survive then it must be colder now than it was then.
    Nothofagus grow at high altitude in SEQ. Not sure how many types but the old Gondwanaland “Antarctic Beech” is not uncommon. Some reputedly 3000 years old, not far from me. [Distance wise, not age.]
    I’ve found that feral cats are like most animals, if they need support to prosper they hang together, if they dont they often split up. I personally observe the neighbourhood domestic ferals meeting in groups in the rainforest and it is not hard to find colonies of a dozen wild ferals further west.
    On the outskirts of some western towns you will also often find a mob of cats together. Many mature males won’t accept hierarchical pack structure and become loners and it’s probably not very relevant to their overall pestilence.
    Barry has identified this possible mass extinction problem due to AGW, however I have to point out that it is going on right now as a result of doing nothing about these feral predators particularly in closer settled, very environmentally significant areas.

  26. Bernard J.
    Can you find out if any of the ground dwelling wildlife in the Snowies [or nearby] still host the paralysis tick [Ixodes holocyclus]?
    This tick is possibly the only thing standing between our ground dwellers and extinction. It is possibly the only parasite that works in favour of the prey rather than the predator.
    I ask people when they extract ticks to “do it gently and put them back carefully”.
    They don’t always feel so disposed.
    Let’s hope that no innoculation for domestic animals or livestock is ever discovered or that will be a death sentence for wildlife.

  27. Spangled Drongo.

    To the best of my knowledge I. holocyclus is pretty much restricted to the relatively warm and humid coastal seaboard of eastern Australia, and isn’t on the ground (or in the trees!) in the Alpine areas. The only link that I have bookmarked is the one I use to explain the risk of tick bites to my field volunteers:

    There is a distribution map linked from this page.

    Perhaps the species has expanded its range (from what I can determine they seem to have been introduced to Tasmania), but tick ecology is not my forte. I doubt though that they would represent a significant bulwark against predation, for the MPP.

    As ever though, Google is our friend, if you want to pursue the matter.

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  36. Barry, would it be correct to say that Its is the rate, frequency temperature impacts and the age of the melting ice that provide evidence of warming not seen since eons.

    Are you aware of references that would support the statement below, or have I got this wrong:

    “Glacial retreats, sea-level rise and the migration of temperature-sensitive species are normal events. It is the rate, frequency of these events, and the age of the melting ice that provide evidence of warming not seen since eons.”

  37. Barry,

    The rebuttal I’m trying make is agaisnts this comment (below mine):

    Glacial retreats, sea-level rise and the migration of temperature-sensitive species are normal events. It is the rate, frequency of these events, and the age of the melting ice that provide evidence of warming not seen since eons.

    “Nonsense. There is no evidence that these phenomenon are unprecedented.”

    Any pointers would be helpful for future discussion.

  38. Unprecedented, no. Unprecedented in human history, yes — vast volumes of evidence, as detailed in 100s to 1000s of peer-reviewed papers (depending on the particular system). Mark, you cannot give a short reply to such dismissive comments — they are made explicitly to get you to waste hours and hours of time trying to respond to something an idiot can type in 5 seconds. My advice, direct them to IPCC AR4 WG I and II reports, and then ignore them henceforth.

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