Extinction and Climate

Life on Earth does not enjoy change, and climate change is something it likes least of all. Every aspect of an organism’s life depends on climate, so if that variable changes, everything else changes too – the availability of food and water, the timing of migration or hibernation, even the ability of bodily systems to keep running.

Species can adapt to gradual changes in their environment through evolution, but climate change often moves too quickly for them to do so. It’s not the absolute temperature, then, but the rate of change that matters. Woolly mammoths and saber-toothed tigers thrived during the Ice Ages, but if the world were to shift back to that climate overnight, we would be in trouble.

Put simply, if climate change is large enough, quick enough, and on a global scale, it can be the perfect ingredient for a mass extinction. This is worrying, as we are currently at the crux of a potentially devastating period of global warming, one that we are causing. Will our actions cause a mass extinction a few centuries down the line? We can’t tell the future of evolution, but we can look at the past for reference points.

There have been five major extinction events in the Earth’s history, which biologists refer to as “The Big Five”. The Ordovician-Silurian, Late Devonian, Permian-Triassic, Late Triassic, Cretaceous-Tertiary…they’re a bit of a mouthful, but all five happened before humans were around, and all five are associated with climate change. Let’s look at a few examples.

The most recent extinction event, the Cretaceous-Tertiary (K-T) extinction, is also the most well-known and extensively studied: it’s the event that killed the dinosaurs. Scientists are quite sure that the trigger for this extinction was an asteroid that crashed into the planet, leaving a crater near the present-day Yucatan Peninsula of Mexico. Devastation at the site would have been massive, but it was the indirect, climatic effects of the impact that killed species across the globe. Most prominently, dust and aerosols kicked up by the asteroid became trapped in the atmosphere, blocking and reflecting sunlight. As well as causing a dramatic, short-term cooling, the lack of sunlight reaching the Earth inhibited photosynthesis, so many plant species became extinct. This effect was carried up the food chain, as first herbivorous, then carnivorous, species became extinct. Dinosaurs, the dominant life form during the Cretaceous Period, completely died out, while insects, early mammals, and bird-like reptiles survived, as their small size and scavenging habits made it easier to find food.

However, life on Earth has been through worse than this apocalyptic scenario. The
largest extinction in the Earth’s history, the Permian-Triassic extinction, occurred about 250 million years ago, right before the time of the dinosaurs. Up to 95% of all species on Earth were killed in this event, and life in the oceans was particularly hard-hit. It took 100 million years for the remaining species to recover from this extinction, nicknamed “The Great Dying”, and we are very lucky that life recovered at all.

So what caused the Permian-Triassic extinction? After the discovery of the K-T crater, many scientists assumed that impact events were a prerequisite for extinctions, but that probably isn’t the case. We can’t rule out the possibility that an asteroid aggravated existing conditions at the end of the Permian period. However, over the past few years, scientists have pieced together a plausible explanation for the Great Dying. It points to a trigger that is quite disturbing, given our current situation – global warming from greenhouse gases.

In the late Permian, a huge expanse of active volcanoes existed in what is now Siberia. They covered 4 million square kilometres, which is fifteen times the area of modern-day Britain (White, 2002). Over the years, these volcanoes pumped out massive quantities of carbon dioxide, increasing the average temperature of the planet. However, as the warming continued, a positive feedback kicked in: ice and permafrost melted, releasing methane that was previously safely frozen in. Methane is a far stronger greenhouse gas than carbon dioxide – over 100 years, it traps approximately 21 times more heat per molecule (IPCC AR4). Consequently, the warming became much more severe.

When the planet warms a lot in a relatively short period of time, a particularly nasty condition can develop in the oceans, known as anoxia. Since the polar regions warm more than the equator, the temperature difference between latitudes decreases. As global ocean circulation is driven by this temperature difference, ocean currents weaken significantly and the water becomes relatively stagnant. Without ocean turnover, oxygen doesn’t get mixed in – and it doesn’t help that warmer water can hold less oxygen to begin with. As a result of this oxygen depletion, bacteria in the ocean begins to produce hydrogen sulfide (H2S). That’s what makes rotten eggs smell bad, and it’s actually poisonous in large enough quantities. So if an organism wasn’t killed off by abrupt global warming, and was able to survive without much oxygen in the ocean (or didn’t live in the ocean at all), it would probably soon be poisoned by the hydrogen sulfide being formed in the oceans and eventually released into the atmosphere.

The Permian-Triassic extinction wasn’t the only time anoxia developed. It may have been a factor in the Late Triassic extinction, as well as smaller extinctions between the Big Five. Overall, it’s one reason why a warm planet tends to be less favourable to life than a cold one, as a 2008 study in the UK showed. The researchers examined 520 million years of data on fossils and temperature reconstructions, which encompasses almost the entire history of multicellular life on Earth. They found that high global temperatures were correlated with low levels of biodiversity (the number of species on Earth) and high levels of extinction, while cooler periods enjoyed high biodiversity and low extinction.

Our current situation is looking worse by the minute. Not only is the climate changing, but it’s changing in the direction which could be the least favourable to life. We don’t have volcanic activity anywhere near the scale of the Siberian Traps, but we have a source of carbon dioxide that could be just as bad: ourselves. And worst of all, we could prevent much of the coming damage if we wanted to, but political will is disturbingly low.

How bad will it get? Only time, and our decisions, will tell. A significant number of the world’s species will probably become extinct. It’s conceivable that we could cause anoxia in the oceans, if we are both irresponsible and unlucky. It wouldn’t be too hard to melt most of the world’s ice, committing ourselves to an eventual sea level rise in the tens of metres. These long-range consequences would take centuries to develop, so none of us has to worry about experiencing them. Instead, they would fall to those who come after us, who would have had no part in causing – and failing to solve – the problem.


Mayhew et al (2008). A long-term association between global temperature and biodiversity, origination and extinction in the fossil record. Proceedings of the Royal Society: Biological Sciences, 275: 47-53. Read online

Twitchett (2006). The paleoclimatology, paleoecology, and paleoenvironmental analysis of mass extinction events. Paleogeography, Paleoclimatology, Paleoecology, 234(2-4): 190-213. Read online

White (2002). Earth’s biggest “whodunnit”: unravelling the clues in the case of the end-Permian mass extinction. Philosophical Transactions of the Royal Society: Mathematical, Physical, & Engineering Sciences, 360: 2963-2985. Read online

Benton and Twitchett (2003). How to kill (almost) all life: the end-Permian extinction event. Trends in Ecology & Evolution, 18(7): 358-365. Read online


82 thoughts on “Extinction and Climate

  1. “ANN ARBOR, Mich.—Rising carbon dioxide levels associated with global warming may affect interactions between plants and the insects that eat them, altering the course of plant evolution, research at the University of Michigan suggests.

    “The research focused on the effects of elevated carbon dioxide on common milkweed, Asclepias syriaca. Milkweed is one of many plants that produce toxic or bitter chemical compounds to protect themselves from being eaten by insects. These chemical defenses are the result of a long history of interactions between the plants and insects such as monarch caterpillars that feed on them.”


  2. I thought John Stoos was joking until I followed his link.

    What would be good to have a citation for, though, would be “Scientists are quite sure that the trigger for this extinction was an asteroid that crashed into the planet, leaving a crater near the present-day Yucatan Peninsula of Mexico”. I thought this was still a bit controversial: yes, most scientists are pretty sure the Yucatan asteroid contributed to the extinction but, as I understand it, many are not sure that it’s the whole or even a large part of the story. Have I missed a change in thinking?

    In 2010, a panel of 41 scientists agreed the asteroid was the trigger, it seems like a pretty strong consensus at this point. BBC has a good article on the paper. -Kate

  3. Greg Craven just helped with a debate between Dimitri Zenghelis (senior fellow at LSE, a principle author of the Stern Report) and Bjorn Lomborg at the London School of Economics (Wednesday). He roped in the “Manpollo crew” to gather info, but the time scale was probably too short.

    However, the debate seemed to go well (i.e. against Bjorn!) – here’s Dimitri’s assessment of how it went

    Greg did a big speech to the AGU (American Geophysical Union) in December which, in his characteristically modest way, he thought he screwed up.

    I think it was one of the most brilliant, passionate speeches I have ever read. What do you all think? Warning – he swears and it’s about as close to the edge as one can go…

    transcript of Greg’s speech

    I’m glad the Lomborg debate went well because Greg was dispirited after the AGU speech, particularly by the impression he gained from the scientists of the real situation we are in. I’ll let him put it in his own words. I always thought that the past extinction events (the subject of Kate’s post) were what makes the most imperative case for dramatic action to be taken to avoid us altering climate and it is disturbing to see what some paleoclimatologists are privately thinking. and planning for…

    Greg’s comment:

    Oh, and one last thing. You deserve the full story, but for now here’s the bottom line: we’re ****ed. AGU rattled me to the core because my worst-case fears were not just confirmed, but exceeded (I found four paleoclimatologists who admitted to making plans for survival retreats), and my last hope–for the scientific community to enter the public debate–was completely dashed.

  4. Once again, your writing – in both quality and output – instills me simultaneously with awe and shame.

    On a related note, there was a recent Nova documentary on human evolution that suggested climate shifts were a primary driver of human cognitive development (i.e. we’re adapted to change, and part of that is our relative ingenuity). It cast this as saying that we were able to survive several climate-induced extinctions through cleverness and emerged just fine – i.e we shouldn’t worry about climate change because we’ll just evolve through it.

    Note the tacit ignorance of rate of change. Note too that it doesn’t mention that evolution works through death, i.e. most of the population would have to die.

    Go to that page (it’s part 1, most of the climate claims are in 2 and 3), and scroll down. See any familiar sponsors?


    You know, I thought Stoos seemed familiar here.

    Ed: As far as paradigm-forming ideas go, the Yucatan asteroid trigger is a relatively recent consensus – the idea that it was an asteroid at all dates back only to 1980. It’s taken 30 years to reach consensus on that idea (though from where I’m sitting, it looked like it gained an unusual amount of support relatively early in its history for an upstart idea).

    …I suppose I could ask how quickly it gained traction directly… the paleontologists at my university are right between my lab and the cafeteria.

  5. It is difficult to assess the magnitude of climate change associated with the events of extinctions in the geological past.

    My subjective view is that the climate change that the human society is inducing is not so strong as to make a great extinction of biodiversity comparable to the events studied by the geologists.

    But I do think that the human impacts on the ecosystem may be so large as to be comparable to those events. It is because of “synergetic effect” between climate change and other human impacts, if I use a technical term used in the following book.

    Thomas E. LOVEJOY & Lee HANNAH eds., 2005: Climate Change and Biodiversity. New Haven CT USA: Yale University Press.

    If climate change happens alone and not too fast, many (though not all) species can adapt by migration. But the human society has made huge land use change that hampers migration. This combination makes extinction of many species likely.

    Impacts to marine ecosystems include, acidification, coastal development, and overfishing. (But, the observed decrease of fish is not always results of human impacts, but also of multi-decadal variation of the physical environment of the ocean combined.)

    So my personal suggestion is that we should not say that anthropogenic climate change will bring a great extinction unless mitigated, but that anthropogenic environmental change will.

  6. “My subjective view is that the climate change that the human society is inducing is not so strong as to make a great extinction of biodiversity comparable to the events studied by the geologists.”

    The associated warming from the Siberian Traps alone is believed to have been around [citation needed], this then may have triggered the release of Methane from land and in the oceans which led to even higher temperature increases.

    Current heating is easily within in the major methane trigger of [citation needed]. It is the secondary responses (methane etc) that are the most worrisome and major effects are potentially with in reach.

    What is the possibility 10%, 1% .01% .0000000001%
    What are we willing to risk?

    Where did you find this Permian temperature change data, Dale? -Kate

  7. The major competitor to the asteroid explanation of the extinction of the dinosaurs is the Deccan Traps (Volcanism in India) which lead to climate change. So even some alternate explanations come back to climate change as the final driving force

  8. Amazing post. Outstanding work.

    I too sometimes approach despondence because of our utter lack, as a society, of taking the problem seriously enough to do something about it. Then I remember that we’ve got you on our side.

    Keep up the good work. We never needed you more than now.

    Thanks for the kind words, Tamino! -Kate

  9. Hmmm, I tried to track down that anecdote and found among other instances this:

    AGU Blogosphere | Mountain Beltway | AGU, day 3
    Dec 16, 2010… already creating some form of survival retreat for their family, … that those four scientists I mentioned were paleoclimatologists, …

    Clicking the link returns: “Fatal Error”

    I tend to agree.

  10. Kate–the Twitchett, and the Benton and Twitchett papers’ links are broken.

    The latter paper is here.

    I can heartily recommend Benton’s book When Life Nearly Died: The Greatest Mass Extinction of All Time.

    Thanks, Ken – I have had that problem with ScienceDirect before, links seem to only work as long as they are in your cache. I will look for alternate links tomorrow, but does anyone have suggestions for the ScienceDirect bug? -Kate

  11. Excellent points on water & how climate change will/does effect the earth’s water…as the water goes, so goes the ecosystems. Good research & post.

  12. Geol 37(9):835-838 (2009)
    Major perturbation in sulfur cycling at the Triassic-Jurassic boundary
    Kenneth H Williford, Julien Foriel, Peter D Ward and Eric J Steig


    “Stable sulfur isotopes from the reduced sulfur fraction of Late Triassic-Early Jurassic marine sediments at Kennecott Point in British Columbia, Canada, show evidence for a major perturbation in sulfur cycling coincident with a major carbon cycle perturbation in the wake of a mass extinction event at the Triassic-Jurassic boundary. The … reduced sulfur shifts from values consistent with open system bacterial sulfate reduction … to values higher than any previously reported for Early Jurassic sulfates … and consistent with complete utilization of sulfate and Rayleigh fractionation in a closed system. We suggest that this isotopic shift was initiated by declining seawater sulfate concentration due to evaporite deposition in nascent Atlantic rift zones and enhanced by a local mechanism, such as a decoupling of the zone of sulfate reduction from the sulfate supply due to a catastrophic increase in the flux of land-derived sediments reaching the sea in the wake of massive terrestrial plant die-off during the Triassic-Jurassic mass extinction.”
    DOI: 10.1130/G30054A.1

    (Ellipses are for characters that didn’t render as text)

  13. Kate, Us old farts will try to hold off the idiots until your generation can take over. I wish we could do more.

    Ed davies said: “I thought John Stoos was joking until I followed his link.”

    Oh, he was joking. He just didn’t realize that he was the joke.

  14. “Where did you find this Permian temperature change data, Dale?”

    I remembered this from a paper I read some time ago, which of course I can’t remember now. So from a quick search on the net starting with wiki

    Recent climate models suggest that such a rise in CO2 (from valcanism) would have raised global temperatures by 1.5 °C (2.7 °F) to 4.5 °C (8.1 °F), which is unlikely to cause a catastrophe as great as the P-Tr extinction.[83]

    Other hypotheses include mass oceanic poisoning releasing vast amounts of CO2[100] and a long-term reorganisation of the global carbon cycle.[97]
    However, only one sufficiently powerful cause has been proposed for the global 10 ‰ reduction in the 13C/12C ratio: the release of methane from methane clathrates;[8] and carbon-cycle models confirm that it would have been sufficient to produce the observed reduction.[97][100]

    the Siberian Traps eruptions were bad enough in their own right, but because they occurred near coal beds and the continental shelf, they also triggered very large releases of carbon dioxide and methane.[54] The resultant global warming may have caused perhaps the most severe anoxic event in the oceans’ history: according to this theory, the oceans became so anoxic that anaerobic sulfur-reducing organisms dominated the chemistry of the oceans and caused massive emissions of toxic hydrogen sulfide.[54]

    From this article’s abstract (which is behind a pay wall)

    “How to kill (almost) all life: the end-Permian extinction event”
    Michael J. Benton and Richard J. Twitchett
    Trends in Ecology & Evolution 18 (7): 358–365.

    “Evidence on causation is equivocal, with support for either an asteroid impact or mass volcanism, but the latter seems most probable. The extinction model involves global warming by 6°C and huge input of light carbon into the ocean-atmosphere system from the eruptions, but especially from gas hydrates, leading to an ever-worsening positive-feedback loop, the ‘runaway greenhouse’.”

    The main question to me seems to be how likely is this type of event now and to what degree are we willing to risk our current balance?

  15. Examples of where continental and submarine supervolcanoes gave rise to Large Igneous Provinces resulting in mass extinction include:

    55 Mya, Paleocene-Eocene Thermal Maximum – North Atlantic Basalts
    65 Mya, end-Cretaceous event resulting from a supervolcano that gave rise to the Deccan basalts in India as it collided with Asia at the time of the formation of the Himalayas
    183 Mya, Toracian Turnover (a lesser warming and extinction event in the Early Jurassic period) – Karoo Basalts (Africa)
    201 Mya, End Triassic Extinction – Central Atlantic Magmatic Province
    251 Mya, Permian-Triassic Extinction that resulted from a supervolcano that left behind the Siberian basalts during the breakup of Pangaea.
    360-375 Mya, Late Devonian Extinction – Viluy Traps (Eastern Siberia, more tentative according to Rampino below)

    For a more extensive list, please see:

    Vincent E. Courtillot and Paul R. Renne (2003) On the ages of flood basalt events, C. R. Geoscience 335, 113–140

    For a recent commentary:

    Michael R. Rampino (April 13, 2010) Mass extinctions of life and catastrophic flood basalt volcanism, PNAS, vol. 107, no. 15, pp. 6555-6556

    Here is recent study showing that the eruption of the Central Atlantic Magmatic Province occured simultaneously with the end Triassic Extinction 201 Mya:

    Jessica H. Whiteside (April 13, 2010) Compound-specific carbon isotopes from Earth’s largest flood basalt eruptions directly linked to the end-Triassic mass extinction, PNAS, vol. 107, no. 15, pp 6721-6725

    One resource well worth mentioning is:

    Large Igneous Provinces Commission
    International Association of Volcanology and Chemistry of the Earth’s Interior

    … and here is a blog that may also be of interest that focuses oftentimes on the intersection of climatology and geology:

    olelog – What on earth

    I believe it is worthwhile to mention these events in deep geologic time anytime someone raises argument that “temperature always rose first.” It didn’t. In some cases carbon dioxide rose first, then temperature. And those times that carbon dioxide rose first are strongly associated with sudden changes in climate and the resulting major and minor extinction events.

    It is also worth noting that these eruptions are on a far greater scale than anything we have seen in the past few million years and are typically associated with the breakup and formation of continents or the formation of ocean plateaus. The Siberian Traps associated with the End Permian Extinction of 251 million years ago (MYA) has a volume of 1.6 million cubic kilometers. The smallest LIP listed is the Columbia River Flood Basalts and it appears to be associated with the End Early Miocene 16 MYA. The volume of that structure is roughly 170,000 cubic kilometers.

    In contrast the the ejecta from the explosive eruption of Mt. St. Helens had a volume of one cubic kilometer, Pinatubo ten cubic kilometers, and the Yellowstone Caldera of 600,000 years ago, roughly 1000 cubic kilometers or 100 Pinatubos going off simultaneously — leaving an ash bed covering roughly half of the area of the 48 contiguous states of the United States is less than 1/100th of the Columbia River Flood Basalt eruption of 16 Mya.

  16. Nice summary, Kate.

    Additional detail is provided in the recently published S. Grasby, H. Sanei and B. Beauchamp paper: Catastrophic dispersion of coal fly ash into oceans during the latest Permian extinction. Nature Geoscience 4, 104-7.

    From the abstract “…Here we present analyses of terrestrial carbon in marine sediments that suggest a substantial amount of char was deposited in Permian aged rocks from the Canadian High Arctic immediately before the mass extinction. Based on the geochemistry and petrology of the char, we propose that the char was derived from the combustion of Siberian coal and organic-rich sediments by flood basalts, which was then dispersed globally. The char is remarkably similar to modern coal fly ash, which can create toxic aquatic conditions when released as slurries. We therefore speculate that the global distribution of ash could have created toxic marine conditions.”

    They go on to document three fly ash loading events at the site, starting an estimated 500 – 750 kyr before the final extinction. The site was an estimated 20,000 km downwind of the Siberian volcanism!

  17. Kate,

    You are now an official member of “The team”. Tamino is propping you big time. You will find any future peer review process much easier. Congratulations.

      • I try and defend myself against an accusation of being slanderous and I get snipped? WUWT?

        In fact, I was out most of today and couldn’t moderate comments, so I hadn’t actually seen your previous comment yet. However, it is indeed “snipped” now, so that was a good prediction on your part. The bit about me being “indoctrinated since kindergarten” was a real gem. -Kate

  18. ScienceDaily (Feb. 19, 2011) — Almost 600 million years ago, before the rampant evolution of diverse life forms known as the Cambrian explosion, a community of seaweeds and worm-like animals lived in a quiet deep-water niche under the sea near what is now Lantian, a small village in Anhui Province of South China. Then they simply died, leaving some 3,000 nearly pristine fossils preserved between beds of black shale deposited in oxygen-free waters.

    Scientists from the Chinese Academy of Sciences, Virginia Tech in the U.S., and Northwest University in Xi’an, China report the discovery of the fossils and the mystery in the Feb. 17 issue of Nature.


  19. A letter in Nature sprang to mind on reading your excellent article above, and may help argue the case with those who doubt anthropogenic influence could produce such extreme alterations in biodiversity

    Extinction risk from climate change

    Chris D. Thomas1, Alison Cameron1, Rhys E. Green2, Michel Bakkenes3, Linda J. Beaumont4, Yvonne C. Collingham5, Barend F. N. Erasmus6, Marinez Ferreira de Siqueira7, Alan Grainger8, Lee Hannah9, Lesley Hughes4, Brian Huntley5, Albert S. van Jaarsveld10, Guy F. Midgley11, Lera Miles8,15, Miguel A. Ortega-Huerta12, A. Townsend Peterson13, Oliver L. Phillips8 & Stephen E. Williams14


  20. Kate, Us old farts will try to hold off the idiots until your generation can take over. I wish we could do more.

    I second Ray’s post. When future generations are tempted to spit on our graves for squandering our planet, let them know there were some who fought very hard for those not yet born (i.e. please don’t lump all of us in with the idiots :-).

  21. Kate, where ScienceDirect has a clickable link to the DOI, right click on that instead and copy the link. Here’s one:

    Twitchett (2006). The paleoclimatology, paleoecology, and paleoenvironmental analysis of mass extinction events. Paleogeography, Paleoclimatology, Paleoecology, 234(2-4)

    I recommend generally posting actual links, because people who print text with links hidden lose the connection to the actual URL. (ScienceDirect causes that problem by hiding the prefix for DOI links, duh.)

    Generally if a link is clickable you can ‘view source’ on the page, copy out whatever they have, maybe lose code like ‘mouseover’ they’ve stuffed in to obfuscate, er, ‘improve the user experience by capturing readers for our advertisers’, and come out with a usable URL.

    I copied the link address that Google Scholar was using, rather than the URL it redirected me to, and I think it’s working now. -Kate

  22. Citing:

    Michael J. Benton and Richard J. Twitchet (July 2003) How to kill (almost) all life: the end-Permian extinction event, TRENDS in Ecology and Evolution Vol.18 No.7

    Dale then asks:

    The main question to me seems to be how likely is this type of event now and to what degree are we willing to risk our current balance?

    As near as I can tell, the Permian-Triassic Extinction was a one-off. Sure, other extinction events involved supervolcanoes, rapid global warming, ocean anoxia and consequent hydrogen sulfide, but nothing approached the Permian-Triassic. And it wasn’t strictly due to the size of the Siberian supervolcano (others resulted in larger flood basalt deposits) or its amplification by the coal fields that were set on fire.

    At the time of the Permian-Triassic Extinction we had a single supercontinent Pangaea. The Panthalassean Ocean had large areas where reduced (low oxygen) rock deposits were forming that were indicative of a stratified, anoxic ocean.

    Please see:

    Yukio Isozaki (11 April, 2007) Permo-Triassic Boundary Superanoxia and Stratified Superocean: Records from Lost Deep Sea, Science, VOL. 276

    Both end-Triassic (~200 MYA) and end-Permian (~250 MYA) show protracted periods of extinction in the ocean, with extinctions leading up to the Permian-Triassic Extinction beginning in the deeper parts of the ocean around 270 MYA, roughly 20 million years before the main event and moving progressively towards land.

    Please see:

    These deepwater, and intermittently shallow-water, H2S-rich conditions were exacerbated by the effects of massive Siberian Trap
    volcanism (Renne et al., 1995; Kamo et al., 2003), which increased atmospheric CO2 concentrations, enhancing the possibility for hypercapnia and/or ocean acidification and biocalcification crises (Knoll et al., 1996).

    Bottjer, David J; Clapham, Mathew E.; Fraiser, Margaret L.; Powers, Catherine M. (Sept. 2008) Understanding mechanisms for the end-Permian mass extinction and the protracted Early Triassic aftermath and recovery,
    GSA Today, v. 18, no. 9, doi: 10.1130/GSATG8A.

  23. Benton and Twitchett (2003). How to kill (almost) all life: the end-Permian extinction event. Trends in Ecology & Evolution, 18(7): 358-365.

    But it’s worth a reminder for people new to reading science that often full text is available; Scholar links to more results and better results than pointing to the publisher with DOI.

    For the Twitchett (2006), putting the author and title into Scholar returns ten other choices including PDF and HTML files.

  24. Your article could be improved by pointing out that two of the major drivers of the Earth’s climate system were different than they have been during the Holocene Epoch. The two drivers are: the amount of energy emitted by the Sun and the size and location of the Earth’s land masses.

    We know that the relatively stable climate of the Holocene Epoch has allowed homo sapiens to thrive and flourish. Has biodiversity in general increased from the beginning of the Holocene to the present?

    In my opinion, any discussion of what the climate was like during geological time periods needs to emphasize how benign to maknkind and relateivly stable the climate has been during the Holocene. We are now on trajectory to create an entirely new Epoch.

  25. All of you people are much smarter than me, so please excuse my simpleton questions. At what level of CO2 in the atmosphere will give us a stable climate?

    • The current level will eventually stabilize, it’s just a matter of when and what that will look like – and if human civilization be compatible with it. (See the end of this comment before replying.)

      You may as well ask “at what point will pressing down the gas pedal give me a steady speed?”Other factors permitting, any level will give you a steady speed – it’s just a matter of what that speed is, and how safe it is for you to be driving like that.

      The IPCC gives numbers calculated on certain conventions – i.e. if CO2 doubles, what’s the corresponding change in stable temperature? For a doubling, these range from 2 to 4.5 C (i.e. for a given temperature and CO2 balance point, if CO2 doubles, you can expect temperatures to climb somewhere between 2 and 4.5 C). Keep that number in perspective when we look at paleoclimate.

      Also keep things in perspective that until the Industrial Revolution (i.e. just before we started dumping fossil carbon in the air), temperatures were lower (see the earlier graph around 1750 or so), but not out of what we’d expect (we certainly had a civilization in that temperature band). Atmospheric CO2 concentrations at that time were around 280 ppm. They’re currently above 390 and still climbing.

      We’re above the speed we’ve been travelling for our entire history, and we show no signs of easing the foot off the gas. And without that step, we won’t be able to stabilize.

      I said above that the “current” level would stabilize. It probably will, if it holds constant. Of course, it shows no signs of doing that on our current carbon course.

      Conclusion? We won’t be stabilizing unless something changes.

      • Brian,

        Thank you for your response. Simpleton question two: Was the climate stable when CO2 levels were 280 ppm?

      • Honestly? I don’t know. In order to provide a meaningful answer, I would need to know the net forcing at the time, and I’m not a paleoclimatologist (I’m merely a psychologist with a background in physics).

        Remember, there are other forcings besides CO2. Anything that alters the amount of energy absorbed by the Earth, be it by increasing the amount coming in (changes in sunlight or albedo (reflectiveness)) or decreasing the amount leaving (i.e. greenhouse gas concentrations) would have an effect on temperature.

        However, I do know that the current trend of sending hundreds of millions of years’ worth of sequestered carbon into the atmosphere in a millionth of the time hadn’t started. So inasmuch as there was a forcing from carbon, it was well within natural variation at that point.

        (Someone more in tune with the physical science, please, correct me if I’m misrepresenting things!)

        I wish I could provide a more meaningful answer (and that I had enough time to study this material in more depth!). There are folks here – or through direct reading over at Skeptical Science – that can help with that. SkS even has basic level versions of its articles written for people with no background in science whatsoever.

        At that time we had long passed the interglacial maximum, so there’s a slight negative forcing from Milankovitch cycles. However, at the same time we were coming up from the Maunder Minimum and LIA, so that would be a bit of positive solar forcing. I don’t think internal cycles like PDO would be characterized as instability, as they don’t change the energy balance, only the energy distribution. On a multi-millennial scale it would clearly have been a cooling towards eventual glaciation (although Hansen had some interesting things in his book regarding whether or not we would have “skipped” an ice age as the Milankovitch cycles shifted from their 10 000 year rhythm into another rhythm). On a centennial scale, though, the LIA rebound is really all I have to go on. Anyone else have thoughts? -Kate

  26. In comparing this essay to an earlier ClimateSight essay entitled “An Unlikely Priority”, I am reminded that when ‘all’ of the science is done, the debate about action on climate change is largely a matter of values and relationships with the world.

    At what point does species extinction become a compelling reason for mitigation?

    If the loss of one species is insufficient, what about 100? 1000? or is it only when the numbers threaten the continued existence of homo sapiens?

    Some claim that mass extinction is just part of the natural cycle, so the risk that we will cause another one is not reason enough to upset the economic apple cart. After all, they say, ‘the planet will still be here’. Some would argue that homo sapiens will have moved on to other planets by then, so who cares?

    I am of the belief that all species have intrinsic value. I hope that it does not take the threat of mass extinction for homo sapiens to decide upon a action plan.

      • John,

        On what do you base your belief that human life has intrinsic value?


      • John,

        Partly a process of elimination :) I am very uncomfortable with the anthropocentric implication of our species assigning (relative) value to other species. Therefore any value must be inherent.

        Largely ‘spirituality’. I think that our modern civilization can be informed by many aspects and learnings of indigenous cultures. “All my relations” has significant implications.

        Along those lines, I found David Suzuki’s “A Sacred Balance” very thought provoking.

      • I guess mine would be based on “spirituality” as well believing that God created man in His image and that we have the responsibility to be good stewards of all the rest of His creation.

        I think you will find that most cultures wrestle with those two very important questions, but only if we know where we and the rest of creation came from can we talk of intrinsic value. Otherwise how do we say to a corporation, you cannot do this or that destructive project?


      • John,

        Setting aside the incredible incoherence of asserting knowledge of where things come from without evidence, you do not actually need to know origins to conclude intrinsic worth. All you need to do is look at what is really there.

        Any interconnected system gains power and resiliency through its constituent parts and the relationships between them. You’ve heard of the food chain? It’s like that, only far, far more complicated. Knock out a single species, and its absence can send ripples throughout not just the local ecosystem, but anything connected to it.

        And we’re connected to it as well. Not just at the food level, either – the second-most-obvious example would be medicine (how many undiscovered cures have we wiped out through deforestation?), along with any natural resource that we get through the living world.

        Biodiversity is its own reward. Just as no individual type of cell is more important than the others, or even necessarily significant on its own, but when put together in a particular way they become you, a whole greater than the mere, disorganized sum of parts.

        This is actually empirical – objectively verifiable, and not based upon any value system except inasmuch as it values “survival” and “quality of life” (which are pretty much universal regardless of one’s ideology). (Aside: Those who would argue the opposite, that species are not intrinsically valuable, I would contend, are dealing with incomplete information, rather than any active malice.)

        As such, what does it matter the basis of reaching that conclusion? The conclusion can be verified and demonstrated from a neutral (or dare I say, secular) perspective, and is thus independent of any particular belief or belief system. No need for claims of origins, nor any unsubstantiated claims of knowledge. Just simple observation, which Christians, Muslims, Hindus, Buddhists and atheists can all do equally well – if they let themselves.

      • Brian – I don’t question the deep interconnectedness of biodiverse ecosystems (or of diverse cells in our own bodies), nor the deep value of individual species within them, though I’m not sure that the argument you have put forward technically supports the intrinsic value of species, since you have pointed to the function of species within a larger system, giving them an instrumental value towards the maintenance of that system. Nothing wrong with instrumental value, of course, and I agree that on this we don’t necessarily need a detailed account of origins to agree.

        John – If you’re interested in a scriptural account of the value of biodiversity, can I humbly suggest this address by noted theologian and biblical scholar Richard Bauckham? It is a summarised version of his new book: The Bible and Ecology: Rediscovering the Community of Creation.

      • Byron:

        Ah, I see what you mean. I apparently had mis-categorized “intrinsic” as somewhat more context-based than it formally is. This probably shows off my empiricist-rationalist bias (as I don’t think you can consider an entity independent of the environment in which it exists – most of my research is actually on the role of the environment as an extension of the mind and as a controller of behaviour). You are right that I made an instrumentalist argument; I was placing value on the system as a whole as an emergent property of its components, rather than on the components themselves.

        If, to make an intrinsic argument, one has to isolate the agent from its environment, then I see how an interrelationship-based argument fails. (To me this sounds sort of like evaluating Shakespeare by isolating it from the English language, i.e. kind of nonsensical, but let’s see where this goes.)

        I suppose that the closest I can get (on short notice) to an empirical argument of intrinsic worth is through the combination of the observed fact of evolution and the theory of evolution: At the population level, creatures alive today are triumphs of natural selection, continuing to survive. In a system that values survival, then that is in and of itself worthy, and such species have intrinsic worth based on that accomplishment. (I don’t like this argument; it’s rather hazy on the value judgments and it still includes the context by which the species emerged (i.e. it includes other species in the species in question’s evolutionary past), so it isn’t completely standalone. Then again, I did reject above that you could do such an argument standalone, so this’ll have to stand for now.)

        (If John pipes up to point out that this is an origins claim, which I pointed out in my earlier argument that we didn’t need to know, I’d like to pre-emptively respond by mentioning that 1- it’s still observed, in much the same way a family tree is observed, and therefore empirical and objective, and 2- evolution does not explain the origins of life, merely the diversity of life (it follows logically from differential environmental attrition and reproduction with variation – it doesn’t care how either of those actually came to be).)

        There is a point I’d like to raise here, though – if, given a species of intrinsic value, we conclude that the members of that species each also have intrinsic value, we have committed a fallacy of division. Similarly, starting with individuals of intrinsic worth and generalizing to the species level is also fallacious (the converse, the fallacy of composition). These would seem to get in the way of performing any of these value judgments at all unless we consider every component, at every level of interest – which implies that a systems perspective is required as part (but only a part!) of this evaluation.

      • Byron,

        Thank you for the link and I hope many others will listen because it will certainly remind us that the Bible has a lot to say on these subjects. Of course I have noticed that anyone like myself who actually believes that Creation and the flood were real events are not taken as seriously.

        While I can agree with many of the points that were made I am sure you know that I have some differences as well. For example, I did notice that the good professor passed over what is said about those large creatures that can be nothing but dinosaurs in the Book of Job as he gives the long list of the others. The other place I would differ is that I believe that “kind” as it is used in reference to animals and plants in the Bible is more likely referring to what we would call Families or Genera.

        However, his bottom line point that Christians of all people should understand that we have a responsibility to be good stewards of the Creation is something I have always stressed. We are the ones who do know why it has value.

        I also enjoyed Brian’s post and will not give him a hard time for getting too close to origins because he shows just how difficult assigning value in a system that denies value really can be. I thought the Shakespeare example was particularly insightful.


  27. Kate, thanks for those links re the KT extinction in response to my Feb 18th 8:28 am comment. I had, indeed, missed something.

    Also, I’d like to echo those who are congratulating and thanking you for your excellent writing here.

  28. Thank you Kate.

    You have a gift for capturing the essence of the important scientific ideas underpinning the issue of anthropogenic climate change, and expressing them clearly and elegantly.

    Your piece summarises— better than my own writing ever could— some of the reasons why we should be concerned about humanity’s current direction of travel.

    There’s still the problem of what to do about it. I see it as a question of scale: scale of certainty, scale of danger, and time (temporal) scale.

    After reading your article I am convinced, more than ever, of the high likelihood of adverse impacts from climate change.

    I’m less clear about the immediacy and extent of the danger. (Actually I’m convinced on the potential extent of danger— as described in the alarming scenarios above— but for many of us humans, this needs to be placed somewhere on the temporal scale: I’d understand if the public considered an existential danger for human civilisation ten thousand years in the future less concerning than severe, though not quite so calamitous, changes twenty or thirty years away- global war, starvation etc.)

    These are the crucial questions when it comes to meshing the science with the messy human social and political arena, because, as Eileen suggests, what constitutes ‘danger’, and what constitutes ‘short’ or ‘long’ term, depends on one’s values and perspective.

    The climate change problem demands farsightedness and at least some form of perceived sacrifices from the developed-world public— at a time when there are many pressing short term problems, and people feel they have a lot to lose.

    I just hope there are win-win solutions out there, and clever people looking for them.

  29. Thank you for such an engaging and important article. What you are doing is so very important. Action is needed, and we are just not seeing it. I am one of those voices for change. Your voice rings so clear, above the rest. I totally support you, and also live in a prairie province in Canada. I can’t believe you are only in “first year”. You are a clear leader, don’t ever stop.

  30. It’s an interesting perspective and a great post. I doubt that our own species will become extinct, but massive die-off would compound other problems associated with projected climate change.

    Kate, it might be worthwhile to include rates of change/time periods in the top post to compare events in the deep past with present. Are we warming/outgassing CO2 as fast as before?

    (I’d follow the links and do the work, but i’m tied up touring a show around Australia, and internet access is squiffy)

  31. Good post. The comments by some others re the location and number of major continents is pertinent on the time scales considered in your post. For example, the “snowball Earth” hypothesis/theory is in part viable because of the contintental structure for the relevant time period, pre-dating the first great extinction event. It took geologic events and orbital changes in order to eventually unwind.

    This doesn’t detract at all from what you’ve written, which is well written indeed.

    Donald Oats

    PS: Peter Ward has a couple of popular science books that delve into anoxic ocean events.

  32. “Species can adapt to gradual changes in their environment through evolution, but climate change often moves too quickly for them to do so. It’s not the absolute temperature, then, but the rate of change that matters. Woolly mammoths and saber-toothed tigers thrived during the Ice Ages, but if the world were to shift back to that climate overnight, we would be in trouble.”

    I understand that the Ice Age was about 5-6C colder in terms of global average temperatures, and that it came to an end over a period of several thousand years, so perhaps 0.1C of warming per century averaged out.

    So we may see anything from 10 to 60 times that rate this century. This strikes me as very likely to lead to significant extinction problems. Would others concur or is this too simplistic a view?

    • Mark, I agree strongly with Kooiti’s statements above–which I have seen him make elsewhere and which show that he has the necessary synthetic understanding that ecology requires. Ecologists do not have the luxury of focusing on climate changes alone. It is *not* climate change per se, but the synergism of climate change with other human caused disruptions, that is the critical issue. I cannot make this point strongly enough–and the issue extends not just to the effects themselves, but also to the scientific process of figuring out what exactly is driving what, how fast, where, etc.

      A couple of other points. Extinction (leaving aside moral/ethical issues for the sake of this discussion) is, relative to other concerns (as Matt mentions above), a problem of the long-term: the slow loss of the individual airplane rivets, what exactly that will do, and when. The much greater concern for many of us is the *destabilization* that will result from population and community shifts–much of which is very difficult to predict with anywhere near the spatio-temporal specificity that we need for any kind of reasonable planning. It is this ecosystem destabilization that far exceeds extinction as the immediate ecological concern. Now people will vary on this issue, but from an ecosystem *functioning* perspective, these shifts in the “balance of power”–and their effects on things like agricultural systems–are of very real concern. To some of us that is.

      Another point is that the demographic vortex processes that drive the vast majority of extinction event processes in the absence of human effects, are now greatly modified–actually or potentially–by the ability to store germplasm and effect translocations, reintroductions etc. This is especially so in plants, even though population of high profile animal species (e.g. wolf re-introductions in Idaho) get far the more publicity (and are also far more expensive). This is a significant difference from pre-history, even though that does not by itself guarantee anything, nor is it anything like an efficient way of going about preserving species.

      What people really need to wrap their minds around is ecosystem destabilization and the havoc that it can create not just in the systems themselves, but also in the understanding of them.

      • I have seen it suggested before that given how difficult our changes to the environment will make migration in the face of climate change that we may find it necessary to interfere once again and aid animals and plants in making the move. But we won’t find it as easy as Noah. We at least have to consider the problem of mutational meltdown via Muller’s Ratchet. So the effective population size in which interbreeding occurs should likely be at least 100. And of course you wouldn’t want all your eggs in one basket, so for any given species you will want several baskets. You also need to consider the dependencies that exists between different species within the same ecological system, and how you will have to move everyone again a few decades later.

      • Yes Tim. It’s very difficult to predict the relative effects of opposing forces of increased barriers, fragmentation etc vs assisted migration, recolonization etc., in the face of a changing climate. Some would say impossible. We have a hard enough time with MVP* analysis when things are stable, let alone when rapidly changing. We have not even remotely close to the information we need to predict what will happen.

        I would add that, IMO, basic issues of demographic stochasticity are much more likely to come into play before inbreeding depression, Mueller’s Ratchet etc., have a chance to act, for many species. Certainly for the obligate out-crossers anyway, of which there are very many. Animals that have bottle-necked recently might be exceptions, but they are a very small % of the biota.

        *minimum viable population

      • Jim,

        Some would say that we can preserve species in the zoo if we are worried about extinction. What would be your take on this?

      • Jim Bouldin wrote:

        I would add that, IMO, basic issues of demographic stochasticity are much more likely to come into play before inbreeding depression, Mueller’s Ratchet etc., have a chance to act, for many species.

        Demographic stochasticity…:

        Demographic stochasticity refers to the variability in population growth rates arising from random differences among individuals in survival and reproduction within a season. This variability will occur even if all individuals have the same expected ability to survive and reproduce and if the expected rates of survival and reproduction don’t change from one generation to the next. Even though it will occur in all populations, it is generally important only in populations that are already fairly small.


        I wasn’t familiar with demographic stochasticity — at least not the term itself. But it reminds me of some of the ideas covered in Bruce Wallace’s “Fifty Years of Genetic Load – An Odyssey.” For example, he mentions how you may have tree seeds that are roughly equivalent, but they may be particularly sensitive to their environment such that there is considerable variability in their development. Some seeds will germinate first. Some will grow more quickly than others.

        If they all grew at the same rate then none would be taller than the others and they would gradually cut off one-another’s sunlight such that the entire “crop” might die due to overcrowding or at least that even those that survived the competition would be considerably weakened. Therefore developmental variability will tend to be selected for. Some individuals rise above the rest — and they keep rising with a smaller set rising above those as time goes on.

        Alternatively some genes may contain hypervariable regions. For example, due to long tandem repeats in protein coding or regulatory regions. In a particularly stable environment their wouldn’t be much benefit in this, but in a variable environment which swings back and forth between extremes what this means is that a given individual may more easily produce offspring where at least some of the offspring will be better suited to the environment — no matter which way it swings.

        The longer the sequence repeats the more subject they are to hypermutation. But where such hypermutation proves detrimental “synonymous” point mutations may act to break up the sequence repeats, reducing the rate of mutation in those regions. In cases where the sequence repeats are in protein coding regions such the amino acids in the proteins themselves will suggest their origin in longer tandem repeats due to the amino acid sequences corresponding to what could be encoded where the sequence repeats on both sides of the point mutation a single continuous sequence repeat. These are known as cryptic repeats.

        David G. King refers to sequence repeats as evolutionary tuning knobs which he and others believe are subject to indirect selection. Here is a page he has with links to articles on this:

        David G. King: Old and scattered links related to simple sequence repeats

        There is also “The Implicit Genome” — a collection of tech articles by various authors in a book edited by Lynn Helena Caporale. At one point it is mentioned that the error correcting enzymes that are used to preserve the fidelity of the genome as it is being copied vary in terms of their ability to maintain that fidelity depending upon the different motifs between the various repeats, and moreover, that this varies from species to species, where some species are better at “error correction” with respect to some repeats but worse at others. And the enzymes used in such error correction are themselves home to hypermutable triple repeats.

        Furthermore, repeats result in intra- and inter-chromosomal rearrangements (e.g., in a more extreme case, the chromosomal fusion that took place after last common ancestor with chimps and bonobos, reducing the chromosomes from 24 to 23) and as such may also be expected to contribute copy number variation of genes and variation in their spatial and temporal expression.

      • Repeats in protein coding regions:

        Mutations in cis-regulatory sequences have been implicated as being the predominant source of variation in morphological evolution. We offer a hypothesis that gene-associated tandem repeat expansions and contractions are a major source of phenotypic variation in evolution. Here, we describe a comparative genomic study of repetitive elements in developmental genes of 92 breeds of dogs. We find evidence for selection for divergence at coding repeat loci in the form of both elevated purity and extensive length polymorphism among different breeds. Variations in the number of repeats in the coding regions of the Alx-4 (aristaless-like 4) and Runx-2 (runt-related transcription factor 2) genes were quantitatively associated with significant differences in limb and skull morphology.

        John W. Fondon III and Harold R. Garner (December 28, 2004) Molecular origins of rapid and continuous morphological evolution, PNAS, vol. 101, no. 52, pp. 18058-63

        More recently repeats in cis-regulatory (“promoter”) regions:

        Relative to most regions of the genome, tandemly repeated DNA sequences display a greater propensity to mutate. A search for tandem repeats in the Saccharomyces cerevisiae genome revealed that the nucleosome-free region directly upstream of genes (the promoter region) is enriched in repeats. As many as 25% of all gene promoters contain tandem repeat sequences.

        Kevin J. Verstrepen et al. (29 MAY 2009)
        Unstable Tandem Repeats in Promoters Confer Transcriptional Evolvability, Science, Vol 324, pp. 1213-16

        Identifying exactly what constitutes a regulatory region is more difficult than the protein coding region since by definition the regulatory region does not get transcribed. Intronic regions may also have repeats that confer greater evolvability but I have as of yet to find studies on this.

        Fun stuff. Of course it really gets interesting once you trace all this back to the Mauriceville retroplasmid. ;-) Maybe later…

      • I have seen it suggested before that given how difficult our changes to the environment will make migration in the face of climate change that we may find it necessary to interfere once again and aid animals and plants in making the move
        It’s already happening: recent example in the UK.

      • Tim, first thanks for taking the time to inform yourself on these–and other–issues, and in general, elevating the level of discussion on such topics wherever you go. I for one appreciate it greatly. We either elevate it or other folks will waste utterly no time in reducing it.

        My opinion on zoos as refuges is that they can be essential for preserving certain highly endangered animal species, but they are in no way suited for a broad scale conservation policy in the face of massive human impacts. They are limited in what they can do, and the eventual re-introductions that are the whole point of such efforts are expensive–hence inefficient–and their probabilities of success almost always uncertain. Germplasm/gene banks and botanic gardens with seed storage facilities greatly extend the possibilities, but you need a lot of them, which requires money. Similar to people who think we can just readily go colonize space if we trash the earth, those who think we can preserve everything in a zoo are divorced from critically important scientific and practical realities. Their over-simplifications are very dangerous and should be countered at every step, as in the recent article about Freeman Dyson’s views about earth’s sustainability at RC.

        Yes, there is definitely selection for genetic variability in populations; this is a very important eco-evolutionary principle that has occupied population biologists/geneticists for a long time. It is absolutely critical in the discussion of extinction probabilities and conservation strategies. A related intra-individual concept is phenotypic plasticity (also under selection): the ability of the individual to alter its development/behavior/life history strategy depending on environmental conditions, which is itself a function of genetic variability, albeit at the individual level (and which caused the early evolutionists, and bunches of plant and animal breeders down through time, a lot of headaches!). This is particularly important in plants–the clade of organisms most under the influence of strong selection by environmental conditions.

        The things you touched on are important too–rates of gene repeat formation, which in turn depend on things like the rates of crossing over during meiosis, the number and activity of transposons in the genome, the capacity for instantaneous polyploidy and speciation (in plants especially), reproductive rate and mean generation time, etc.

        All of which make the topic pretty damn fascinating.
        And important.

  33. Kate:

    The information conatined in the following article may or may not be news to you. It’s about new findings re the cause of the extinction which occurred in the late Ordovician Period when more than 75 percent of marine species perished

    “Link Between Ancient Climate Change And Mass Extinction” posted on SOTT.net on Feb 18, 2011


    ‘Link Between Ancient Climate Change And Mass Extinction

  34. Very nice post.

    FYI, quick typo note… the sentence below seems to end before it’s completed:

    …releasing methane that was previously safely frozen in.

    A quick run through (just bullet points) of all five extinction events would be useful, too.

    This brief article at SkepticalScience is good (it discusses rate of change as well as degree of change in CO2 as a factor in the extinctions):

    Earth’s Five Mass Extinction Events

  35. Why does everyone think it will take “centuries” for these effects to occur?

    How fast could the oceans go anoxic? Consider how many “dead zones” have occurred in the last 40 years. It is non-linear and poorly modeled process. We can plot them by volume/ year and look at the percentage increase per year. That is scary. However, ocean temperature is a major factor in anoxic oceans and plotting volumes of ocean water with positive temperature anomalies per year suggests that large areas of the oceans could go faster than our plotted “percentage increase in dead zones per year” and much faster than “centuries in the future.”

    I am not saying the oceans will go anoxic soon, I am saying that our best models do not include known feedbacks, and thus saying that we have centuries before the problem is immediately life threatening is really nothing more than “irrational exuberance”

  36. Kate,

    Honestly I think you did a great job with article. People are going to tell you that you should have included this, that or the other thing. Not like you really need advice, but for others…

    It is always possible to include more things. When someone suggests including something else, consider it — with a grain of salt. Otherwise the essay can quite easily lose focus. Its like writing a novel. You may have great characters, great scenes, etc., but if they don’t actually contribute to the story you should leave them out.

    Meanwhile thanks to the people who brought up additional points. It gives others more to explore — and things that can be explored in greater detail in other essays.

  37. The “Age of Man” is now a hot topic!

    The following paragraphs are from “Welcome to the Anthropocene” posted on Climate Central.

    “Nobel prize-winning chemist Paul Crutzen brought the idea of the Anthropocene into the scientific spotlight in 2002 (Crutzen is famous for having studied atmospheric chemistry relating to the hole in the ozone layer), but it is not yet an accepted term in geology vernacular. However, in the March 2011 issue of the Philosophical Transactions of the Royal Society A, a group of researchers are attempting to make the case that the profound human-driven impacts on the planet in recent years fit the criteria for a new geological distinction.

    “In this month’s issue of National Geographic magazine, journalist Elizabeth Kolbert writes about the Anthropocene, and she points out that it is surprising which kinds of human behavior are expected to have the longest-lasting impacts (from a geologic perspective, at least). The skyscrapers, the highways, and the suburban sprawl?”

  38. “The more complicated and interconnected the food web, the less damage you can expect if one or two species are lost,” explains Deborah Bronk, a biological oceanographer and specialist in nutrient cycling at the Virginia Institute of Marine Science at the College of William & Mary. “In these very simple food chains, if you lose one species you can really mess up the whole thing.” Complexity yields resilience.

    Without resilience, there’s risk of a crash. Scientists who study trophic cascades, in which the loss of a single species sets off a reaction throughout the food web, report that this sort of crash generally happens in low-diversity ecosystems, where one or a few species exert great influence.

    That describes the Arctic marine and coastal food web.

    The above paragraphs are from “Arctic Fever” posted today (Feb 23) on NRDC’s OnEarth.


    • I’ll take this as a chance to make one final, relevant comment on this topic:

      The types of information Kate presents here is important in informing possibilities for catastrophic changes due to large changes in the earth system–and hence what could potentially occur in the future. Similar to other types of paleo- studies, this gives us context and some sense of worse-case scenarios that are to be avoided.

      However, for any sort of effective planning, we need much, much more detailed, mechanistic understanding of the processes that drive extinction. These are biological, ecological and genetic in nature. This is very similar to the difference between the information that paleoclimatic reconstructions give us (a descriptive, historical context) and the information that climate models and the analysis of instrumental data give us (a mechanistic understanding of cause and effect). Without this bottom-up approach, the top-down contextual information is much less useful.

  39. A terrific piece, about which I have one question:

    “As a result of this oxygen depletion, bacteria in the ocean begins to produce hydrogen sulfide (H2S) instead.”

    Instead of what? There’s no referent that I can find.

  40. Chris,

    Some anaerobic bacteria that produce hydrogen sulfide and other bacteria produce oxygen. The anaerobic bacteria find oxygen poisonous and therefore remain below the oxycline, a boundary between oxygenated waters and anoxic waters.

    What we call blue-green algae are a variety of species of cyanobacteria — which produce oxygen as part of the process of photosynthesis. Some cyanobacteria took up residence in the leafy plants found on land by becoming chloroplasts. Most eukaryotic algae is similar to leafy plants in that they too have chloroplasts. And as such free-living cyanobacteria and symbiotic chloroplasts produce oxygen as part of the process of photosynthesis.

    The problem with today’s algae blooms off the Oregon coast and Namibia is that land warms more rapidly than ocean, creating a high pressure zone by the coast. This causes upwelling of water from below providing more nutrients for the algae, but it also diminishes the water circulation that would otherwise carry the algae out to sea.

    When the algae dies its decay uses up the oxygen in the water, moving the oxycline up, but it also provides nutrients for the anaerobes below. Their populations increase and some of them produce hydrogen sulfide.

    Hydrogen sulfide and oxygen undergo a chemical reaction of the form:

    2 H2S(g) + 3 O2(g) —> 2 SO2 + 2 H2O.

    This is in fact the chemical reaction that is largely responsible for maintaining an oxycline. Therefore increasing the amount of hydrogen sulfide reduces the amount of oxygen in the water and further pushes the oxycline towards the surface.

  41. ChrisD, you had quoted from the main essay:

    As a result of this oxygen depletion, bacteria in the ocean begins to produce hydrogen sulfide (H2S) instead.

    … then asked:

    Instead of what? There’s no referent that I can find.

    There it sounds like the bacteria was producing something other than H2S, but then begin producing something different.

    However, the “instead” in this case attaches to the oxygen that would have been mixed in by turnover — as is suggested by the previous sentence:

    Without ocean turnover, oxygen doesn’t get mixed in – and it doesn’t help that warmer water can hold less oxygen to begin with.

    So with turnover you would have oxygen entering the ocean from the atmosphere near the poles (where colder water is able to absorb higher concentrations of gases — including both oxygen and carbon dioxide), but without turnover you have increasing levels of hydrogen sulfide.

    Returning to my previous comment, I would of course expect the oxygen from cyanobacteria to (primarily) enter the atmosphere first, that is prior to entering the general circulation of the ocean. For one thing, photosynthesis takes place within the first few meters of the surface rather than being mixed more generally throughout the ocean. Perhaps ten meters in clearer tropical ocean water — which is clearer because of the reduced levels of algae. Which means that on average the oxygen will tend to get produced at shallower depths.

    Once the oxygen is in the atmosphere it will enter the ocean primarily through Arctic and Antarctic waters as part of deep water formation where the water will get drawn down and circulated through the rest of the ocean. Raising the temperature of the water will decrease its ability to carry oxygen, too, but the diminished circulation and stratification Kate mentions are far more important in causing anoxia.

    Yes, the “instead” meant that the oceans would be full of hydrogen sulfide instead of oxygen. I agree that it doesn’t make grammatical sense, I will take it out! -Kate

  42. Quick point: natural languages always have ambiguities. You work to try and eliminate the big ones but at some point have to rely upon the context to establish what you mean. (Of course I have the added handicap of having taken just enough German to ruin my English grammar. Or so my wife tells me.)

  43. This quote struck me

    “The modern global mass extinction is a largely unaddressed hazard of climate change and human activities,” said H. Richard Lane, program director in the National Science Foundation’s Division of Earth Sciences, which funded the research. “Its continued progression, as this paper shows, could result in unforeseen — and irreversible — negative consequences to the environment and to humanity.”


  44. Hi Kate
    I’m one of the editors of a web page about climate change writing in Icelandic (loftslag.is). Can we have your permission to translate this post?

    Hoski Bui

    You are more than welcome to do so! Thanks for your interest! -Kate

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