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Tuesday, 29 April, 2008

Can animals and plants adapt to global warming?

Guest post by Barry Brook, Director of the Research Institute for Climate Change and Sustainability at the University of Adelaide.

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.


Figure 1: Southeast Asian extinctions projected due to habitat loss (source: Sodhi, N. S., Koh, L. P., Brook, B. W. & Ng, P. K. L. 2004)

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 2: 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.

Professor Barry Brook is an international research leader in global ecology and conservation biology. He holds the Foundation Sir Hubert Wilkins Chair of Climate Change and is Director of the Research Institute for Climate Change and Sustainability at the University of Adelaide. He has published two books and over 120 scientific papers on various aspects of human impacts on the natural environment and biodiversity, including climate change, deforestation and overexploitation of populations. In 2006, he was awarded both the Australian Academy of Science Fenner Medal for distinguished research in biology and the Edgeworth David Medal by the Royal Society of New South Wales, and in 2007, the H.G. Andrewartha Medal by the Royal Society of South Australia and was listed by Cosmos as one of Australia's top 10 young scientists. The principal motivation for his research is to identify ways and means of reducing extinctions and mitigating the worst ravages of global change.

Brook, BW et al. 2008. Synergies among extinction drivers under global change. Trends in Ecology and Evolution, in press (email: barry.brook@adelaide.edu.au for a preprint)

Posted by Barry Brook at 11:29 AM

Comments

  1. Excellent post. Extinction cycles and their causes are one of my favorite studies. An extinction cycle weeds out less adaptive species and creates diversity amongst the more flexible species. It should be interesting to see P.E. in action. In fact we may already have seen it in some of those newly discovered species in the same area of the world. This could be a very interesting thread.
  2. Quietman, what's P.E.? You seem to be promoting the idea that extinction is "good" because it improves opportunities for the surviving species. Although it's obvious that niches that have been opened invite evolutionary explosions among surviving lineages, I think it's unclear that extinctions are "good". Before I get too worked up about it, I should ask exactly what you mean. I should also ask what you mean about newly discovered species. Are you talking about new speciation events or new description of products of ancient speciations?
  3. Steve L
    P.E. is the Punctuated Equilibrium hypothesis put forth to exolain rapid changes in evolution on the species level. In Gould's view mutations occur under stressed conditions more rapidly, increasing diversification. In this view, while the parent species may become extinct, its offspring live on as several new species, of which at least one lineage has a higher probability of survival. In this light, there is no net loss, only change.
  4. Quietman,

    on your description of Punctuated Equilibrium (P.E.):

    ["P.E. is the Punctuated Equilibrium hypothesis put forth to exolain rapid changes in evolution on the species level. In Gould's view mutations occur under stressed conditions more rapidly, increasing diversification. In this view, while the parent species may become extinct, its offspring live on as several new species, of which at least one lineage has a higher probability of survival. In this light, there is no net loss, only change."]

    I'm not sure that's a good description of Punctuated Equilibrium for several reasons, and you seem to be (correct me if I'm wrong) pursuing the notion that man-made extinctions (present and future), are a rather jolly wheeze from the point of view of interesting potential observations (your first post seems to indicate that).

    Here's some of the problems:

    1. It's unlikely that mutations occur more rapidly under stressed conditions, if by "mutations" you mean the DNA-level mutations that underpin the evolutionary process.

    2. Eldredge and Gould, as far as I remember, didn't specify "stressed conditions" in relation to P.E. The main mechanistic element of P.E. is the existence of sub-populations of species, either at the physical margins of the population range, or completely isolated from the main species population. In these instances mutations don't occur more rapidly. However mutations are not diluted through the main species pool, and so may be maintained in the sub-population. In fact speciation within P.E. might occur by genetic drift. The major element is population-isolation rather than population-stress.

    3. P.E. is neutral with respect to diversification. P.E. scenarios resulting in increased diversification can be formulated (there's evidence for these) as can P.E. scenarios resulting in none, or even decreased diversification (there's evidence for these too) although the latter would involve more widespread consideration of a particular ecosystem.

    The latter is the concern with respect to global warming within a world with already fragmented and denuded ecosystems as indicated in the excellent summary by Barry Brook at the top of this section.

    Clearly over the significant human-scale term (10's, 100's, 1000's of years) exctinctions are going to continue to increase, so (whatever the joys of potentially "observing" P.E. on the hoof!), we're not going to see diversification. Secondly, it's not obvious that we're likely to have enhanced opportunities for observing P.E. on the hoof anyway. In fact the opposite is far more likely. Never mind the fact that speciation events require many generations, and so we're unlikely to see these in animals on human timescales anyway. In a world of fragmented and denuded ecosystems there are likely to be less speciation events to observe. After all we can already observe incipient speciation under P.E. type scenarios (e.g. "ring species"), and it's questionable whether things are going to be more interesting in that respect in a world with even higher levels of species extinction.
  5. Chris

    The comment is about how the species will adapt as was specified in the title to the blog. So adaptation, not extinction is the subject (no offense meant).

    My remark about it being interesting is simply that I have studied paleontology, extinction and evolution for over 40 years as a hobby so I appreciate a Blog on my favorite subject.

    P.E. was actually a Darwinian conceot that he mentioned in "On the Origin of Species". Both Darwin (in his writings) and Gould (in TV intervies) spoke about environmental pressures causing sudden jumps in evolution, and that is the part of PE that I refer to.

    The most recent study of extinction cycles is out of USC Berkely and they found an average rate of 62 million years. This should place us within the error bounds of an extinction cycle right now which seems to have begun about 10,000 years ago, the cause of which is climate change, as is the end cause of every major extinction regardless of the trigger mechanism.

    Extinction of a species happens constantly, its natural and the species is replaced by something else. An example is the polar bear, not a true species by definition, but a variation of the grissly bear. The Species is not endangered but a variation or subspecies is. That is how evolution works, although the polar bear is not actually in danger of extinction and the likely result will be hybrisization.

    What I found interesting is not the extinction but the new species cropping up in the more tropical climates. especially SE Asia and South America. They are new discoveries but are they small populations because of an extinction or because they are brand new species of the Holocene? I wait with anticipation for the DNA results.

    None of this is heartless or cruel, its just how nature works.
    [ Response: The article is about extinction. The premise is "will animals adapt or become extinct". In fact, the original title was "will global warming cause a mass extinction event?" but I changed it. Now wondering if I was mistaken. ]
  6. Re: "we're not going to see diversification"

    I have to disagree on this point. We have already seen diversification within the Holocene. The same Polar/Grizzly Bear exaample serves. It is one species that we did not recognize as one because they were/are in the process of speciation (Darwin's mutation and variation in isolation). Hybridization is already showing up as their habitats begin to overlap. Hybridization can lead to a new subspecies as well. If subsequently isolated speciation would occur eventually as well.

    The comparison of the geologically short time that hominids have existed can not be validly compared to the thousands of years prior. If you want to use the past century, it needs to be compared to a similar sized slice of the past. This is a common error when trying to compare trends. The likelyhood of the slope of a single century resembling that of an epoch is extremely low. Its like apples and oranges, they both may be round but there the similarity ends.
  7. Quietman, I have an interest in evolution too and work as a biologist studying salmonids. I say that because I think I disagree with large portions of what you've written, and I don't want you to think it's because of a lack of evolutionary perspective on my part. One place we could start is with polar vs grizzly bears. I pick this one because it's topical wrt an impending decision re ESA listing. (Is that why you chose that example?) First argument: Ursus arctos vs Ursus maritimus -- they are described as distinct species; hybridization is not enough to say they are only subspecies unless you apply a strict "biological species concept" (Mayr). You can search for many articles describing the difficulties in applying that concept. You might like to read this paper, too (I'm a coauthor): http://tinyurl.com/5fdax5
    Second argument: under the ESA, distinct population segments can be listed as species. That is, the legal definition of species does not follow the biological species concept.
  8. Sorry, I should apologize for the US-centric view assumed in the above comment. I refer there to the ESA of the United States and a decision on polar bears to be made by the US gov't.
  9. Quietman,

    You can't separate adaptation from extinction in the context of global warming. If the title of the thread is "Can animals and plants adapt to global warming?" the answer must contain the probability that for many species the answer will be no. No means extinction. There's rather clear from Barry Brook's analysis and from what we have observed already in relation to habitat destruction and impoverishment.

    There's no such thing as an "extinction cycle". There are extinction events that have causes (most likely climatic changes in the broadest sense as you indicate). So the Holocene extinction is not part of some grand "cycle", and describing it as such can suggest the notion that it's either inevitable or nothing of much concern (after all it's just another part of the "extinction cycle"!) In fact it's an extinction that relates to man-made destruction and impoverishments of habitats, and it's likely to be exacerbated in a warming world. It is an issue that we can choose to address or not.

    I don't see your point about diversification in relation to polar and grizzly bears. Of course species have diversified in the past (polar bears likely split from the ancestral species from a couple of 100,000 years ago). The past has seen a glorious diversification of species to give us the richness of the natural world which man-kind has already rather significantly reduced especially during the last couple of centuries. If one considers the fate of bears now and in the future it's not a rosy one. For example, the possibility that polar bears become extinct as their habitat disappears in a warming world is a significant one. Unless wilderness areas are maintained there won't be any bears at all, since bears and mankind are incompatible outside of zoo's and circus's...considering bears overall, extinction is a rather more likely future than diversification...

    That's really the point. In the deep past speciation/diversification occurred with speciation events likely taking 100's of 1000's of years (much like the polar bear speciation/diversification). Every so often massive climate change (resulting from extraterrestrial impacts or from massive tectonic events, for example) resulted in very widespread extinctions. These events weren't associated with diversification since, in general, most of the species of interest were unable to adapt. They went extinct without diversification. It was only following the recovery to more stable environments that the evolutionary process allowed the recovery of an impoverished post-cataclysmic biosphere, and this recovery, which was associated with rather widespread speciation/diversification as habitats were repopulated took many millions of years.

    So we need to be clear about where we are. Yes we have seen some speciation/diversification during the Holocene (the evolution of freshwater seals in Finland is a better example, since this is a truly post-glacial event), but we've seen far more extinction. The combination of continued habitat destruction combined with a very rapid warming is very likely to see this trend accelerating into the future. Yes there will be many species that survive and a few may diversify in response to habitat/climatic changes in the coming 100's and 1000's of years. But on the whole the biosphere will continue to become impoverished. If we have 500,000 species of "interesting animals" (say the size of a child's fist and larger!), and we watch 200,000 of these disappear (unable to adapt = extinct), while 100 (say) undergo diversification to new species, I think we would agree that the richness and diversity of the biosphere has become degraded.

    In recognising where we are, we have the ability to address these issues, since we're very much part of it all. We're not bystanders observing some inevitable "extinction cycle" and 'though we might be enthused by the possibility of P.E.-type diversification within those species that are able to adapt to an impoverished natural world, I would consider that future generations would be rather more enthused by the possibility that we might now be taking steps to minimize the impoverishment of the natural world which they will inherit.
  10. Steve L
    I understand what you are saying, there is more than one definition. I database fossil species primarily so I look at living species from a evolutionary point of view. I see polar bears as speciation in progress, so calling them a species as far as legal terms go, I don't have an issue with and that is not why I used them. I used polar bears because everyone is somewhat familiar with them on an international level. Coyotes are not as well known but are another example of speciation in progress.
  11. chris

    I do not disagree that there is a possibility of these extinctions. But I do feel that in most cases diversity must and will occur, just as descibed by Darwin, but that it will be new species that survive, not the parent species.

    Re: "There's no such thing as an "extinction cycle"."
    That is not a fact. It has not been proven one way or the other. The Berkeley paper is a hypothesis, and if correct, we are in one now. The evidence so far is very good that we indeed are. Are you denying that there are climate cycles as well?

    I agree with your closing statement. We should indeed protect the environment to minimize stress on these animals, but that does not make it less interesting from an evolutionary standpoint.

    By the way, I am somewhat skeptical about the current causes of climate change. So from my point of view much of this is natural. But that is irrelevant to my statements here, as I am not advocating that we just let them die. So please do not be offended by my scientific curiosity.
  12. Quietman,

    I'm going to answer each of your points sequentially:

    ["I do not disagree that there is a possibility of these extinctions. But I do feel that in most cases diversity must and will occur, just as descibed by Darwin, but that it will be new species that survive, not the parent species."]

    I think you're being over-theoretical here. If one dissociates oneself from extant reality and views our situation as an interested bystander, no doubt one can conclude that the present extinction period, will in time (we're talking many 100's of 1000's to millions of years), result in a rediversification of life on Earth. All very interersting from a Darwinian perspective no doubt.

    However if we are interested in our extant reality and that of our descendants over the next decades, 100's and even 1000's of years, then we might want to put those academic considerations aside and focus on the reality. And the reality is that continued habitat degradation exacerbated by continued global warming is going to produce an inpoverished biosphere.

    Since we're not disinterested bystanders, but are in fact an integral causal part of these processes, we might want to consider doing something to address the problem (which we are, as it happens, since there are many efforts underway to protect wilderness areas, and there are growing efforts to address the problems of man-made global warming).


    ["Re: "There's no such thing as an "extinction cycle"."
    That is not a fact. It has not been proven one way or the other. The Berkeley paper is a hypothesis, and if correct, we are in one now. The evidence so far is very good that we indeed are. Are you denying that there are climate cycles as well?"]
    Fair enough. However one has to be careful here. Let's say that the Berkeley paper [Rohde and Muller, Nature 434, 208 (2005] is correct. You say that means that (referring to extinction "cycles") "...we are in one now. The evidence so far is very good that we indeed are".

    But that is to take the passive attitude to ridiculous extremes. The natural world is not in the process of undergoing a large-scale extinction because of some ill-defined, uncharacterised "cycle" in which we find ourselves helplessly unlucky enough to find ourselves!. It is in the process of large-scale extinction because of large-scale habitat destruction and the other human practices described in Barry Brook's article at the top of this thread. We're part of it.

    Now are there extinction cycles? Perhaps there are but the evidence isn't very strong. It's possible that the extinction/diversity events only appear to follow a cycle, but aren't cyclic at all. After all there's rather good evidence that the end-Cretaceous extinction
    65.5 million years ago (mya) was due to an extra-terrestrial impact perhaps supplemented by the massive tectonic events which formed the Deccan Traps in now-India. The extinctions at the Paleo-Eocene Thermal Maximum (55 mya) was likely due to the tectonic events (and massive release of methane) associated with opeining up of the North Atlantic plate boundary. The Triassic-Jurrasic extinction (201.6 mya) associates with the massive volcanic outpourings of the central Atlantic magmatic province.....The huge Permian-Triassic extinctions (252.5 mya) appear to coincide with the tectonic events resulting in the Serbiamn Traps formation....and so on.

    Are these events part of some huge cyclic phenonenon during Earth's history? It seems unlikely. The most "popular" notion of the origin of the 62 my "cycle" is long term cyclic variation of the cosmic ray flux (CRF). But how does that relate to tectonic events on Earth? It's difficult to ascribe any sort of connection.

    I suspect that the extinction/diversity cycles only appear to be "cyclic". However even if they truly are part of a grand cycle, that obviously doesn't account for the current extinctions. Is the world undergoing massive tectonic processes during the past 200 years? No. Are we being blasted by a massively enhanced CRF all of a sudden. No.

    We know what is causing the current extinction. It ain't some magical "cycle". It would be foolish to sit back passively and suggest such a thing...

    ["Are you denying that there are climate cycles as well"]

    Which "climate cycles"? There is an 11 year solar cycle. There seem to be cycles associated with ocean circulation. There are the climate cycles associated with the slow variations in the orbital properties of the Earth (Milankovitch cycles). But what other cycles are you considering? Again the same argument applies. Whether or not there are "climate cycles", we know that the current very marked warming of the last 30-odd years isn't due to any of the cycles that we know of. It's very likely to be due to man-made enhancement of the Earth's greenhouse effect.

    By suggesting that everything is "natural" (we're in a "natural extinction cycle"; we're in a "natural warming cycle") we might conveniently absolve ourself from any imperative to address these problems. In fact we know with a very high degree of probability that the current extinctions are not part of some "natural cycle" and the the current warming is not part of some "natural cycle". The evidence is overwhelming on the first and very strong on the second.

    Clearly if these were "natural" then the must have some explanation in terms of "natural phenomena". So what are these "natural phenomena"?
  13. John
    In your comment to chris you mrntion a title change. I think that you chose the better title as AGW may make the event worse but did not start the event which has been going on for a very long time. We, as a species, have only barely survived this event and are in a diversification stage ourselves. My personal belief is that this event is nearing an end and we will be the winners if we get our act together.
  14. chris
    You are asking me to give an answer that that thus far has been unanswerable. I can only give you my philosophical view.

    For starters, my view of our part in extinctions is a natural one. We are animals struggling for survival. In our struggle we have made many mistakes and to correct them is the obvious thing to do. But because we are a part of nature the term "man made" warming is referring to our mistakes and not outside of nature.

    The current AGW is the point of contention. Will it cause extinction on its own. No, I do not feel that our errors alone are a cause but they certainly don't help.

    Should we save the polar bears, No. First, I don't believe that they need any help. Second, they are a competitor to us as a species, we eat the same food and occupy the same habitat. Our duty is to our species, not to a species in competition. The save the bears thing is an emotional issue, not a darwinian issue. We need to concentrate on helping species that are beneficial to us, regardless of the actual cause of their stress.

    As for the cyclic nature of the universe, that would take a lot more room than John has on this server. We need to stay on a point to point basis, like PDO and the Atlantic cycles, the vulcanism and gravitational pressure that drive them and the solar cycles, each has a place but not in this thread.
  15. chris

    Since you chose the KT event as an example, I can addrss that event. The cyclic influences, Sun's Movement Through Milky Way Regularly Sends Comets Hurtling, Coinciding With Mass Life Extinctions *1. This gives a slightly xhorter cycle than the Berkely study.

    But the dinosaurs were already in decline before the Yucatan impact and before the eruption of the Deccan Traps due to a cooling climate which they could not adapt to. Their problem was that Dinosaurs Probably Lacked Tissue To Generate Heat *2. Vulcanism and the impact pushed them over the edge.

    There are a lot of forcing cycles for climate change and for extinctions vulcanism and impact cycles also must be included (see Johns PDO title, the solar titles and the volcanos title for just a few).

    *1 Adapted from materials provided by Cardiff University
    *2 Adapted from materials provided by New York Medical College
  16. Quietman,

    There are two issues here. One is the reality of our present impact on the biosphere and the additional consequences of global warming on a natural world suffering the effects of habitat destruction and fragmentation. That's what Barry Brook's article is about.


    The second is about the causes of previous extinctions and the possibility of cyclic causal factors. These can be addressed separately, since while past extinctions are clouded in various uncertaintites, the present extinction is not.


    So I'll address the current extinction in this post and the possibility of cyclic contributions to past extinctions in another. Notice that the possible contributions to past major extinctions are (whether cyclic or not) variously: tectonic events; catastrophic extraterrestrial impacts; changes in greenhouse gas concentrations (CO2; methane) resulting in global warming or cooling that may be associated with tectonic events or impacts; sea level changes; variations in the cosmic ray flux...(we might come up with some others...)


    NONE of these apply to the current extinction event even 'though the enhanced greenhouse contribution is likely increasingly to do so (that's the subject of this thread if you remember!). The last several thousand years, and especially the last several hundred years has NOT seen extinction-level tectonic events, extraterrestrial impacts, massive sea level changes, very large and persistent changes in the cosmic ray flux; large changes in greenhouse gas levels and so on...


    So the current extinctions are not a consequence of any of these, nor a consequence of any unspecified grand "cycles". They’re a result of mankind’s impacts on the biosphere, especially habitat destruction and fragmentation. Let's not pretend that we don't know what we do know!


    The problem with the attempt at passive dissociation from these realities is that it leads to a rather disinterested acceptance of events that might very well be in our control to address. So let's look at these:


    (i) You consider that our part in these processes (direct extirpation of species by hunting or persecution; habitat destruction and fragmentation; more recently, massive release of greenhouse gases) is a natural one. That certainly applies in the past; however not only is that an unhelpful notion in the present context (it lends to passive acceptance of issues we might otherwise address productively), but at some point that notion breaks down, at the very least at whatever time in our history we start to recognise the wider consequences of our actions, and it’s implications for our futures. So it’s not really “natural” anymore by most generally recognized meanings of the term.


    But however we might semanticize our present situation ("natural"/"non-natural"), the fact is that we might decide to address the problems since we recognise and understand these. We might choose to address policy that limits destruction of habitats and allows these to extend somewhat; we might take further measures to protect ocean species by setting up protected no-fishing respite zones in the manner that is being undertaken already; we might take measures to limit greenhouse gas emissions, and to curb human population growth...in fact we have to do some of these sooner or later…the only meaningful long term future for mankind is one based on stable populations in societies fueled by renewable energy sources for example, and that future starts rather soon!


    (ii) you suggest that we shouldn't "help" polar bears since they’re apparently a "competitor to us as a species" and "we share the same habitat" and "eat the same food" and "we should concentrate on saving species that are beneficial to us". Fair enough...but what a dismal philosophy if I may say so. After all why not kill off all species that we can't productively convert into domesticated animals for food, furs, milk, and other bits and pieces? And in what way is the polar bear a "competitor" which "shares or habitat" (Arctic continental margins and sea ice?) and eats the same food (seals?)? Mankind has co-existed pretty comfortably with polar bears and there's no reason why we can't continue to do so. It may be that the polar bear is doomed because its habitat is not going to survive the likely destruction of Arctic sea ice. But let’s recognize that that will be a diminishing prospect for us and the natural world and one that we might take careful note of, especially in relation to more effective protection of wilderness areas.


    There is a philosophical issue here of which Barry Brook’s article highlights one side and your posts highlight a rather extreme other. On the one hand, we can make mature and rational attempts to inform ourselves about the natural world, our place within it and our impacts, as indicated by careful observations and analysis, and then address these in relation to concerns about our wellbeing and that of our near descendants (who will themselves have to address these issues)…


    ..or on the other hand, we can sit back and wash our hands of the whole affair, using as justification for our passivity, pseudoscience notions of “natural” “cycles”, which we are apparently helpless to explain and understand.
  17. Quietman,

    On cycles and explanations for previous extinctions:


    Hunting around for the latest press releases and popular science articles as all-encompassing “explanations” for past events isn’t very helpful or scientific. Scientific explanations require a set of rather more self-consistent data and theoretical frameworks. A very recent paper that indicates that dinosaurs may not have had the genes for generating brown adipose tissues (the article in Science Daily that you urled), does not suddenly become the explanation for the demise of the dinosaurs, let alone the more widespread extinctions associated with the end-Cretaceus events! The possible lack of adipose tissue in dinosaurs certainly wasn’t the cause of end-Cretaceous extinction of ammonites, mosasaurs, plesiosaurs, various birds and mammals, plants and invertebrates, and so on..


    In fact, if you read the paper referred to in your popular news article [N. V. Mezentseva et al (2008) “The brown adipocyte differentiation pathway in birds: an evolutionary road not taken”; BMC Biology 6 (17) 21 April 2008], you’ll see that the authors don’t mention dinosaur extinction at all (the words “extinct” or “extinction” don’t appear in their paper). No doubt the popular press article that you urled was “sexed up” by an editor to give it a punchy general appeal.


    The fact is that the end Cretaceous extinctions were not due to the possible lack of brown adipose tissue in dinosaurs, although that might or might not have contributed to the demise of that particular order. Regarding the dinosaurs, it’s rather more likely that the widescale attenuation of photosynthetic activity for a few years following an extraterrestrial impact was more than sufficient to kill off large herbivores and their predators. For the extinction event overall, the evidence indicates a combination of an extraterrestrial impact with a long term tectonic events associated with the Deccan Traps formation in non-India as the likely causal factors [e,g Beerling et al (2002); Keller (2005); Kelley (2007)].


    But was the end-Cretaceous extinction part of a regular “cycle” of extinctions? The evidence isn’t very strong. You describe Wikramsinghe and Napier as indicating a 36 million year (my) cycle of extraterrestrial impacts that relate to passage of the solar system through the galactic plane. That paper isn’t available yet apparently, but a recent similar study by Napier [“evidence for cometary bombardment episodes” Mon. Not. R. Astron. Soc. 366, 977-982 (2006)] doesn’t present that compelling a case for a regularity of impacts. And after all, in the paper you previously cited as evidence of the cyclic nature of extinctions [Rohde and Muller, Nature 434, 208 (2005 )], the extinction “cycle” was supposed to be 62 my. You presumed from that study that we are “presently in one now” (i.e. an extinction, since the period is 62 my, and the last one was around 65 mya). However if the extinctions are actually supposed to “cycle” with a 36 my, then we shouldn’t be in an extinction now at all! So which is it?


    I suspect the problem relates to the search for “cycles”. The cosmic ray fluxers look at the extinction record and see a 140 my “cycle”; the astrobiologists “see” a 36 my “cycle”; Rohde and Muller “see” a 62 my “cycle”. It’s rather easy to “fit” sinusoidal variations into very sparse data sets (rather few extinction events; rather few impact craters; rather limited fossil record). I don’t have any problem with the possibility that there might be regular variations in the cometary intensity due to passage of the solar system through the plane of the Galaxy. The problem is that the evidence isn't that compelling, and there is really only one extinction event (end-Cretaceous) that has good evidence for a causal impact event.


    More compelling (to me!) is the data that focuses carefully on the extinction events themselves to identify features of the contemporaneous geological record to determine potential associated geological and environmental effects. When one does this, the most regular correlate of extinctions is tectonic events (doesn’t necessarily indicate causality of course!). A very recent reanalysis of the argon-argon dating “clock” has established, for example, that the massive Permian Triassic extinction correlates with the massive volcanic events associated with the formation of the Serbian Traps (see Science 25th April 2008)]. The end-Cretaceous extinction (dinosaurs et al) correlates with the tectonic events associated with the Deccan Traps formation. The Paleo-Eocene Thermal Maximum extinctions with the tectonic events associated with the opening up of the North Atlantic at a plate boundary. The Triassic-Jurrasic extinction (201.6 mya) associates with the massive volcanic outpourings of the central Atlantic magmatic province…and so on...


    Are these tectonic events governed by grand “cycles”. There’s no evidence for such a cycle, nor is there evidence for any causal attribute of periodicity in these processes.


    Actually, when one boils down the essential correlates of extinctions as these are best defined, the evidence indicates that global warming (as the result of the release of greenhouse gases) seems to accompany most extinction events, and that’s one of the compelling reasons for attempting to get to grips with these difficult to study events in the deep history of the Earth!

    ----------------------------------------------

    Beerling DJ et al. (2002) An atmospheric pCO(2) reconstruction across the Cretaceous-Tertiary boundary from leaf megafossils; Proc. Natl. Acad. Sci. USA 99 (12): 7836-7840

    Keller G (2005) Impacts, volcanism and mass extinction: random coincidence or cause and effect?; Austral. J. Earth Sci 52 725-757.

    Kelley S. (2007) The geochronology of large igneous provinces, terrestrial impact craters, and their relationship to mass extinctions on Earth ; Journal of the Geological Society 164, 923-936

    etc..
  18. chris

    Thank you for the responses. My personal position is not as extreme as you might believe, in fact its closer to yours than average, I just don't get emotional about it. As I said, we, as a species, have made mistakes by not taking better care of the habitats that we live in and should attempt to correct these mistakes.

    I am not saying that the answer is to do nothing, but pointing out that our concentration should be on area that needs it the most like the Amazon deforestation issue.

    What I attempted to point out with polar bears is that they are adaptable, they are not actually in danger of extinction while other species are. With limited resources we should concentrate on the species that are both truely endangered and of greater benefit to both ourselves and out habitats. In doing so we will also be helping less endangered species like the polar bear.

    Barry Brook is pointing out the endangered areas, of SE Asia. While concerned, I feel we need to look in our own back yards first. By helping the ecology here we can do our small part. This however does not mean that I believe that extinctions over the past 10K years are not natural or that the endangered animals currently under stress were not already under stress, just more so.
  19. chris

    On cycles and explanations for previous extinctions:

    I used those 2 articles simply because they were the most recent, not actually the most relavent. As you are aware the idea of extinction cycles is just hypotheses,
    while the idea of climate cycles has good evidence. In the case of the KT event, some paleontologists have pointed out that the dinosaurs were in decline from about 70 million years ago due to climate stress. The effect of the Deccan Traps and the Yucatan impact seem to be a fatal blow but most likely not within a cyclic extinction (my view). The PT event also involved an impact and the Siberian Traps but did they actually cause the climate change or again were they a coincidence that simply made things worse?

    The issue of clarity in climate cycles is simply that there are too many of them and not all of them identified as yet. Why do ice ages occur? Of the 4 major iceages why are they of different lengths and what causes their end. Are we now coming out of an ice age of merely within an interglacial? There are definate cycles involved but we still have a long way to go in understanding them.

    And I agree, Global warming does seem to be directly related to extinctions and I believe that it is the speed not the temperatures that are relavent. The warming slopes are much steeper than the cooling slopes, not allowing enough time for species to adapt.
    I simply disagree that mankind is the direct cause. But I feel that our mistakes have only made things worse.
  20. Quietman

    We know reasonably well well why ice ages occur. In the general case, major glacial epochs (we're in one now) are associated with low atmospheric CO2 levels. For example the present glacial epoch began during the Miocene. The early Miocene glacial period around 20 million years ago (mya) is associated with the late Oligocene-early Miocene decrease in atmospheric CO2....the middle Miocene climate optimum (so-called) with a rise of atmospheric CO2, and then the late-Miocene expansion of the East Antarctic ice sheet is associated with a drop in atmospheric CO2 around 14 mya [*****]

    Of course these glacial periods also require other factors...for example the Miocene glaciations that heralded the start of the cool period which we're still in, wouldn't have occurred (or at least not to the same extent) without a land mass in the Antarctic for ice to build up on....

    Likewise the earliest glacial epoch on Earth more than 3 billion years ago was likely the result of the evolution of the first photosynthetic organisms that produced oxygen which eventually (after turning enormous amounts of oceanic iron salts into iron oxide) destroyed (oxidised) the high methane concentrations that was then "helping" to warm the early Earth.

    As for the ice age cycles within the current glacial periods, these are also quite well understood, as I'm sure you know. They result from the slow cyclic variations in the orbital properties of the Earth (google Milankovitch cycles) that result in slow and small variations in the pattern of solar irradiation on the Earth. These cycles have associated variations in greenhouse gas concentrations (especially CO2).

    I think it's quite clear that we are in an interglacial period which still has quite a few thousand years to "run".


    [*****]e.g. Kurschner WM et al. (2008) The impact of Miocene atmospheric carbon dioxide fluctuations on climate and the evolution of terrestrial ecosystems; Proc. natal. Acad. Sci. USA 105, 449-453.

    Abstract: "The Miocene is characterized by a series of key climatic events that led to the founding of the late Cenozoic icehouse mode and the dawn of modern biota. The processes that caused these developments, and particularly the role of atmospheric CO2 as a forcing factor, are poorly understood. Here we present a CO2 record based on stomatal frequency data from multiple tree species. Our data show striking CO2 fluctuations of approximate to 600-300 parts per million by volume (ppmv). Periods of low CO2 are contemporaneous with major glaciations, whereas elevated CO2 of 500 ppmv coincides with the climatic optimum in the Miocene. Our data point to a long-term coupling between atmospheric CO2 and climate. Major changes in Miocene terrestrial ecosystems, such as the expansion of grasslands and radiations among terrestrial herbivores such as horses, can be linked to these marked fluctuations in CO2."
  21. chris

    I agree to some extent but feel that CO2 does not play as big a role as you indicate. Its primarily a feedback mechanism and needs something to feedback from, that is why there is a lag to temp increases. Asd you mentioned Milankovitch cycles, these appear to be a major climate driver but not the only one. Then there is the Fairbridge sea level cycles and his last hypothesis about solar (system) cycles, about which Mackey did a paper on after Dr. Fairbridge passed away. AGW is about an artificial CO2 feedback but there is also a very real natural CO2 feedback mechanism.

    PS - In my original comment "interesting" was in reference to the potential comments opened up by this particular subject which I am much more familiar with than climate science.
  22. Looks like we did it again"
    "'Unintended Consequence'
    The decision to place polar bears under the protection of the Endangered Species Act came in response to the continued "loss of sea ice," the bear's natural habitat, that would put them "at risk of becoming endangered in the foreseeable future," according to a statement by the Department of the Interior on May 14.
    There is no mention that the danger to polar bears stems from hunting.
    In the same statement, Secretary of the Interior Dirk Kempthorne specifically noted that "limiting the unintended harm to the society and economy of the United States" was a concern.
    What did not seem to be a priority, however, was the harm to the economy in Arctic Canada, home to about two-thirds of the world's polar bear population, which is estimated at 20,000 to 25,000."
    [ABC (US) News]

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