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Earth's five mass extinction events

Posted on 15 April 2010 by John Cook

As climate changes, a major question is whether nature can adapt to the changing conditions? The answer lies in the past. Throughout Earth's history, there have been periods where climate changed dramatically. The response was mass extinction events, when many species went extinct followed by a very slow recovery. The history of coral reefs gives us an insight into the nature of these events as reefs are so enduring and the fossil record of corals is relatively well known (Veron 2008). What we find is reefs were particularly impacted in mass extinctions, taking many millions of years to recover. These intervals are known as "reef gaps".

Mass extinction events and periods of coral reef regrowth
Figure 1: Timeline of mass extinction events. The five named vertical bars indicate mass extinction events. Black rectangles (drawn to scale) represent global reef gaps and brick-pattern shapes show times of prolific reef growth (Veron 2008).

There have been five mass extinction events throughout Earth's history:

  1. The first great mass extinction event took place at the end of the Ordovician, when according to the fossil record, 60% of all genera of both terrestrial and marine life worldwide were exterminated.
  2. 360 million years ago in the Late Devonian period, the environment that had clearly nurtured reefs for at least 13 million years turned hostile and the world plunged into the second mass extinction event.
  3. The fossil record of the end Permian mass extinction reveals a staggering loss of life: perhaps 80–95% of all marine species went extinct. Reefs didn't reappear for about 10 million years, the greatest hiatus in reef building in all of Earth history. 
  4. The end Triassic mass extinction is estimated to have claimed about half of all marine invertebrates. Around 80% of all land quadrupeds also went extinct.
  5. The end Cretaceous mass extinction 65 million years ago is famously associated with the demise of the dinosaurs. Virtually no large land animals survived. Plants were also greatly affected while tropical marine life was decimated. Global temperature was 6 to 14°C warmer than present with sea levels over 300 metres higher than current levels. At this time, the oceans flooded up to 40% of the continents.

What caused these mass extinctions? To find the major driver of coral extinction, Veron 2008 looks at the possible options and eliminates many as the primary cause. A meteorite strike is capable of creating huge dust clouds that lead to devastating darkness and cold. However, if this were the cause of coral reef extinction, 99% of the world's coral species would be wiped out in weeks or months. The fossil record shows coral extinction occurred over much longer periods.

Warmer temperatures cause mass bleaching of corals. However, even in a warmer world, deep ocean temperatures would still remain well below surface temperatures and there would be safe havens where cooler water upwells from the deep ocean. That's not to say meteorites or global warming played no part in coral extinction - both have been contributing factors at various times. But they cannot fully explain the nature of coral extinctions as observed in the fossil record.

What Veron 2008 found was each mass extinction event corresponded to periods of quickly changing atmospheric CO2. When CO2 changes slowly, the gradual increase allows mixing and buffering of surface layers by deep ocean sinks. Marine organisms also have time to adapt to the new environmental conditions. However, when CO2 increases abruptly, the acidification effects are intensified in shallow waters owing to a lack of mixing. It also gives marine life little time to adapt.

So rate of change is a key variable in nature's ability to adapt. The current rate of change in CO2 levels has no known precedent. Oceans don't respond instantly to a CO2 build-up, so the full effects of acidification take decades to centuries to develop. This means we will have irretrievably committed the Earth to the acidification process long before its effects become anywhere near as obvious as those of mass bleaching today. If we continue business-as-usual CO2 emissions, ocean pH will eventually drop to a point at which a host of other chemical changes such as anoxia (an absence of oxygen) are expected. If this happens, the state of the oceans at the end Cretaceous 65 million years ago will become a reality and the Earth will enter the sixth mass extinction.

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Comments 1 to 50 out of 74:

  1. IPCC's 2007 report predicted that ... "20 to 30 per cent of plant and animal species assessed so far are likely to be at increased risk of extinction if increases in global average temperature exceed 1.5 - 2.5 °C" above current levels" But you can see the issues with their "assessment" at www.NewScientest.com
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  2. Karl_from_Wylie But when you read the New Scientist article, you find "But when New Scientist contacted the authors of those critiques, none demurred from the IPCC finding. One, John Harte at the University of California, Berkeley, said most of his criticisms suggested that Thomas underestimated extinction rates. Far from the IPCC being guilty of exaggeration, he says, its caution may have led it to underplay the extinction holocaust awaiting the planet's biodiversity in the coming century." So one of the big issues with the IPCC process is that they often end up being conservative to build consensus statements.
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  3. Fine subject for discussion Mr. John. A possible explanation for these extreme events is in the soil sealing caused by excess ammonium in the soil derived from the decomposition of organic matter. This is not "peer-rewied" but it is a matter to be discussed because in the sealing soil, the rain water does not infiltrate. It runs through the surface and goes straight into the oceans. To balance the evaporation rate of water into the atmosphere nature calls for the warming of the oceans. This sealing is a natural cause and is verifiable olso in forest soils. Here in Manaus the infiltration of water into the soil goes up to 20 cm depth only. With the lack of water to evaporate soil temprature in summer reaches 48 degrees centigrade. This problem must be present throughout the intertropical zone. In the Americas, Africa and New Zealand.
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  4. #2 cbrock The point of the article, is how can conclusions be trusted if the methodology is questionable.
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  5. Which methodology, Karl? Can you be more precise?
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  6. I haven't managed to get hold of Veron's paper, so it's premature for me to comment on it. However, there were reefs in the Palaeocene, after the K/T event. A big decline in reefs seems to have happened later at the Palaeocene-Eocene thermal maximum. Reference
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    Response: Here's a link to the full version of Veron 2008.

    Thanks for the link to Decline of coral reefs during late Paleocene to early Eocene global warming (Scheibner 2008). I'm building a list of peer-review papers on the risks to coral reefs and have added this paper.
  7. Re #4 Karl_from_Wylie: I'd echo Doug Bostrom's question in #5 above. I'd also add this one: if the only identified flaws in a methodology are that it underestimates adverse impacts of CO2 emissions, should we not take action to mitigate the impacts that it predicts? Or should we wait until we know with more certainty how bad the train wreck is going to be before we think about applying the brakes? Call me cynical, but that's like saying "Hey, this analysis suggests only some of the passengers in the first carriage are going to be killed, but there are some train experts who think it could be worse, so hold off on that brake lever until we figure out exactly what's going to happen."
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  8. #5 doug_bostrom Please see the points the author made at NewScientest Although the author supports the ultimate conclusions, the entire article challenges the methodologies of the IPCC. I question whether one can support conclusions if the methodologies are not acceptable.
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  9. #7 Bern Call me cynical, it like saying, "Hey I don't agree with your methods but your conclusions agree with my pre-concieved conclusions on the issue, so you're study is good."
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  10. I am struggling to follow your logic. The article states: "The investigation reveals that the IPCC's broad conclusions were sound. Indeed, the stringent rules of the IPCC means the report sometimes understated the potential impacts of climate change - on biodiversity, for instance. But our findings suggest there may have been problems with the way its conclusions were presented." In what way does this imply that the methodologies are wrong and thus the conclusions cannot be trusted? If the criticism is that methodologies lead to underestimation, then surely you conclude that the conclusion should be taken as best case, rather than of no value at all. Highlighting some areas for improvement in not a reason to chuck the baby out with the bath water as the investigation clearly and unequivocally states.
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  11. Hi John, when I last read the Veron paper it seemed to me that some of the CO2 reconstructions didn't seem wholly congruent with what I'd seen elsewhere. Now, looking at Veron's figure 3, I wonder how it would compare (and how the question marks reflect uncertainty ranges). I'd like to see the most recent and best or consensus reconstructions of atmospheric CO2 and marine pH. Two minor comments: (1) for the end Cretaceous, you say "tropical marine life was decimated," but decimated has two common uses. Which usage do you mean? (2) At the end you say Earth will enter the 6th mass extinction, but many biologists say that the 6th extinction is well underway. I thought it was Stuart Pimm, but Google disagrees -- the idea precedes 1995.
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  12. Karl (#8) not to leave your last post unanswered, it's really not possible to have a productive discussion about nonspecific complaints. But the article hardly seems a ringing indictment: We focus on three key topics: the impact of climate change on water supplies, food, and biodiversity. The investigation reveals that the IPCC's broad conclusions were sound. Indeed, the stringent rules of the IPCC means the report sometimes understated the potential impacts of climate change - on biodiversity, for instance. Going on, we see some details of the "flawed methodology" you refer to. We've got the Thomas paper, which was criticized this way: when New Scientist contacted the authors of those critiques, none demurred from the IPCC finding. One, John Harte at the University of California, Berkeley, said most of his criticisms suggested that Thomas underestimated extinction rates. Far from the IPCC being guilty of exaggeration, he says, its caution may have led it to underplay the extinction holocaust awaiting the planet's biodiversity in the coming century. The article goes on to discuss a problematic report on drought, where instead of 179 million persons at risk of water shortage, the net turned out to be "just" 40 million. A gaffe alright, but not an indication that nothing's happening, eh? Finally there's the matter of crops yields in Africa (again). A clear case of the IPCC ending up with a squishy conclusion. But anything in the article questioning the basic premises this entire matter hinges on? No. And anything talking about exaggerated extinctions, in the New Scientist article? Any problems with hyperbole noted? No, the opposite. And I can just about guarantee that by now we'd have heard of 'em, if such there were. After all, New Scientist looked into that specific issue, right? So I don't agree with you, Karl. I don't see a refutation of multiple avenues of mainstream science or a reason to seriously imagine we've got thousands of researchers on a delusional path. Nope.
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  13. This is just about reef ecosystems?
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    Response: Veron 2008 uses the fossil record of coral reef extinctions to glean certain facts about past mass extinctions - by looking at the nature, timing and geographical spread of coral extinction, they deduce that global atmospheric CO2 levels changed dramatically during each of the 5 mass extinctions. While ocean acidification was devastating to marine ecosystems, obviously other factors were in play such as the mass extinction at the end Triassic where 80% of all land quadrupeds also went extinct.
  14. 2.cbrock "John Harte at the University of California.... the extinction holocaust" I was critised for suggesting alarmist were peddling catastrophes and asked to show examples of scientists doing this. You may have just done that for me. The particularly wording Prof Harte uses here is the most offensive language imaginable.
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  15. "In the Late Devonian period 75 million years, the environment that had clearly nurtured reefs for at least 13 million years turned hostile and the world plunged into the second mass extinction event." I don't understand what you're trying to say here. To what do the "75 million years" and "13 million years" refer?
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    Response: Sorry, that should be "75 million years ago". Around 75 million years ago, there was a period of 13 million years when corals were thriving. Then things went horribly wrong...
  16. Here John, for your list on reef references. http://www.nova.edu/ncri/11icrs/proceedings/files/m25-06.pdf Looks at real world areas of the ocean aftered by ENSO to suggest what may happen to reefs worldwide with increasing CO2.
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  17. ...and the Earth will enter the sixth mass extinction. What is the definition of a MEE? It seems to me that we are entering one now. I think we should be referencing what we are seeing now not as a Climate Crisis, but as a Mass Extinction.
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  18. Hey, John, do you have a reference on the anoxia outcome?
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    Response: I was just quoting the Veron paper - I suggest reading through the paper, following any references and report back to let us know what you find :-)
  19. @ 15 James Wight Response: Sorry, that should be "75 million years ago". Around 75 million years ago, there was a period of 13 million years when corals were thriving. Then things went horribly wrong... Yabbut that wasn't in the Devonian (which was 354-410 million years ago)... :-)
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  20. Re #15 response According to Wikipedia, the Devonian spanned 416 to 359 million years ago, and the main extinction event was about 364 million years ago. So where does the "75 million" come from?
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  21. Sorry, I meant to link to this Wikipedia page.
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  22. I have copied Figure 1 above to a carbon dioxide history reconstruction. You can see that CO2 either changes fast or not at mass extinction events. The same is true for times of prolific reef growth. Also, reefs can happily grow with carbon dioxide levels above 2000 ppmv, sometimes.
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  23. You and Veron (2008) are inferring rapid C02 changes and ocean acidifications at mass extinction periods by looking at coral reef extinctions. This inference has little/no evidence to support it, other than circumstantial. Corals reef extinctions and coral reef 'absences' in the fossil record occur for other reasons than by rapid C02 changes and inferred ocean acidification. "Throughout Earth's history, there have been periods where climate changed dramatically" Wrong/selective. Most mass extinction events occurred in geological times of tens of thousands of years. This is not what is generally meant by "change dramatically". Your point 2 above should say 75 million years later, not "ago". This Later Devonian event didn’t 'turn hostile’; it was a slow process, with multiple waves, that occurred over millions of years. The Mass extinction at the end of the Permian was caused by cascading factors that occurred over several hundred thousand to a few million years, related to Siberian Traps volcanism. Most genera took about 10 Ma years to recover, the corals were not in any way special. The End Triassic mass extinction (I think it is actually Mid Triassic) was associated with Gondawana continental breakup and injection of vast rift-related volcanism in South America, Australia, South Africa and Antarctica. Most of the hard rock aggregate on the East Coast of Australia, the towering cliffs in Tasmania, South America and so on are associated with this. It was volcanic, and slow, like most mass extinctions. The End Cretaceous was associated with Deccan Traps volcanism in India (not long after it separated from Africa) and bolide impact. This is the only certain mass extinction event associated with bolide impact, but volcanism played a major part as well (a one two punch). “The fossil record shows coral extinction occurred over much longer periods." This is because it was a result of slow, gradual, volcanically active periods. They were not periods of 'quickly changing atmospheric c02'. They were periods of slow increases in volcanism. Veron is not a volcanologist. Neither was Alvarez, who rejected both the stratigraphers and the volcanologists who informed him his bolide impact theory in 1980 at the K/T boundary wasn't all that was going on at the time. Time proved the volcanologists right, and as usual, the physicists who like to dabble in earth history got it wrong eg: • Kelvin and the age of the earth early 1900s, when stratigraphers told him the earth was much older than his calculations-he wouldn’t listen ; • the geophysicists and other non-earth physicists -including Albert Einstein-who rejected plate tectonics in the 1920s-1950s - the stratigraphers told them the rocks proved the continents moved well before plate tectonics was discovered, • Alvalrez and bolide impact 1980s, and • John Cook solar physicist 2008- now inferring mass extinctions of corals were rapid and associated largely with rapid c02 changes, I suspect most volcanologists would say this is a gross oversimplification, or at worst invalid. There is little/no evidence that slow volcanic processes were associated with inferred ocean acidifications, and corresponding reef extinctions. The reefs went extinct, like most other things, because of slow sea level changes (there is good correlation betwen sea level changes and marine extinctions), changes in volcanism (producing a variety of slow effects-again a very good correlation, but importantly-generally not with C02 changes), bolide impacts (really the only one that is 'rapid'), continental break ups (eg Triassic), continental joinings (well known to reduce biodiversity as previously separate and endemic species compete with and then extinguish each other), and many other factors. C02 change is slow, doesn’t follow these other factors or most mass exticntions, and plays a relatively minor part in the history of the earth. You're selective references to the vast peer reviewed literature on mass extinctions does not give readers the full picture of the state of understanding and history of debate in this field.
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  24. For once, I have to disagree with one of your postings, John. You present a very speculative study as far more definitive than it really is. Vernon may be right about ocean acidification being the coral killer, but the case is certainly far from proven, and may never be. I think your claim that dramatic climate change always produces mass extinctions needs major qualifications added too. The PETM was a pretty dramatic temperature increase, for instance, but it led only to a very minor marine extinction extinct. More recently, there have been some dramatic climate changes with no evidence of associated extinctions - the so-called Quaternary conundrum. Other experts I've spoken to (I've been writing a related article) say this could just because no one has looked at the fossil record closely enough, but the jury is certainly still out on this issue. Otherwise, though, a great site with great content - keep up the good work!
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  25. Paulm: I think it's perhaps slightly premature to call what's happening at the moment a mass extinction event (MME), however if there are intelligent creatures around on Earth in a few million years time perhaps they'll refer to the period we're rapidly moving into as the 'AME' -- Anthropogenic Mass Extinction. Sounds a lot more serious than 'anthropogenic global warming', does it not?
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  26. Hi John you mean 75 million years later here since your first bullet item was the end Ordovician: "75 million years ago in the Late Devonian period, the environment that had clearly nurtured reefs for at least 13 million years turned hostile and the world plunged into the second mass extinction event." I have to agree with Michael Le Page though I too think your site is one of the best. Except for the K-T, most major and minor mass extinctions don't lend themselves to unilateral causes. This may be why they are so rare. However, anthropogenic impacts are not just CO2 or climate related. We may be having an even bigger impact on the nitrogen cycle for example so John Russell may also be correct. We may be changing too many aspects of the Earth system too fast. Tony
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  27. Re #23, John you're in pretty good company there! Thingadonta, this may be your best comment here ever, but I have some questions about it. First, you're suggesting that changes due to volcanism over tens of thousands of years are too slow to be compared to what's happening now? Since excess CO2 will remain in the atmosphere for a long, long time, I don't see what you're complaining about. A dramatic change over the course of centuries will not have less impact than the same amount of change over thousands of years. Second, genera taking 10 million years to recover after mass extinctions -- I suspect that you mean the diversity within genera took a while too develop after the pruning that mass extinctions did to the evolutionary tree. But that's not what reef gaps are. Reef gaps are periods of no reef building. Sure, the biodiversity is reduced, but you don't need all of the species to build a reef -- a limited complement of species should be able to do it. So apparently conditions not conducive to coraline growth (low pH) persisted.
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  28. Thanks, John. I need to lean a little less on your excellent synopses and drill through into the citations a bit more.
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  29. A few quibbles, Thingadonta. It's not John Cook who's inferred the possibility of an acidification-related extinction but Veron. So you can take John off your list of physicists making predictions later found wrong. In any case a collection of mostly dead persons are irrelevant to this particular paper. The fact that coral population collapses may occur for reasons other than those Veron surmises says little about his hypothesis. I can think of analogies and so can you, but suffice it say that one failure mode does not exclude another. With reference to past events you say "C02 change is slow", but the change we're concerned with here and now is swift and this is the particul. I committed the sin of failing to drill through John's synopsis and thus was left with a poor understanding of Veron's case. Now that I've actually scanned Veron's paper, I see he's gone through this subject with substantial attention to detail and makes a pretty thorough accounting for his hypothesis. If you've not read it, you ought to do so. Then it would be interesting to see what you say regarding the paper and its claims specifically, as opposed to remarks about typographic errors in John's post and generalizations about past personalities and events.
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  30. Full text of Veron 2008 here: Mass extinctions and ocean acidification: biological constraints on geological dilemmas
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  31. #14 HumanityRules The phrase "the extinction holocaust" is not a direct quote from the scientist, so you might want to reconsider whether this really represents a scientist "peddling catastrophes". But let's stick to the scientific topic at hand, shall we?
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  32. There is new research suggesting that the major factor in the Cretaceous extinction was the Chixculub impact, not the Deccan volcanoes. I'm trying to find the Science article mentioned here: LINK 

    I recall reading that bolide impacts could also be triggers for the kind of activity that left behind the Dekkan Traps and Siberian Traps, but can't find the reference at the moment. In any case, things must be considered in context. The pressure of Human activity and the size of the population alone are enough to drive numerous species to extinction. Rapid environmental changes happening at the same time won't help.

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    Moderator Response:

    [RH] Shortened url.

  33. Thanksfor the link paper, One question before I may respond more fully (I am in the remote field at the moment using VSAT satellite collecting real data in the real world, and not making up pretty coloured models on a computer screen, and of course, who am I having to deal with right now, people using pretty coloured maps on a computer screen which are wrong and exagerated and which I am fixing in the field with real data, but I digress). my question: -the Siberian Traps ejected vast volumes of eg c02 over several hundred throusand years+, and it took coral reefs to collapse over hundreds of thouands of years (and possibly, oceans to acidify-although this is not clear) hso how can less amounts of c02 from humans acidiy the oceans in a few decades-hundreds of years??
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  34. @ Philippe Chantreau post 32 Are we talking about the K-T boundry line here and the creataceous mass extinction event? I thought his was regarded as the mainstream/consensus view. I understand there is still some debate on the issue. What is the most recent peer revieweed lit on this? However, SciAm referenced a study here as the "definative consensus view" on the issue.: "...A group of 41 researchers have pored over the evidence and decided that—in accordance with the original postulate put forth 30 years ago by a team led by father and son researchers Luis and Walter Alvarez—it was, indeed, a massive asteroid that slammed into Earth, creating Chicxulub Crater on Mexico's Gulf Coast, that killed off many of the species on the planet, including the non-avian dinosaurs. The review, published online March 4 in Science, evaluated the whole picture, according to Kirk Johnson of the Research and Collections Division at the Denver Museum of Nature and Science and co-author of the paper. And that meant assessing the other theories that have been put forth about what spelled death for the dinosaurs..." Study published in Science here : "...The temporal match between the ejecta layer and the onset of the extinctions and the agreement of ecological patterns in the fossil record with modeled environmental perturbations (for example, darkness and cooling) lead us to conclude that the Chicxulub impact triggered the mass extinction." [from abstract]
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  35. #23 Steve RL. "So apparently conditions not conducive to coraline growth (low pH) persisted". IE for ~10Ma. In the case of coals, there is a 'coal gap' between 250 Ma to ~240 Ma, the plant species that produced most of the coal in The Late Permian went extinct at the end of the Permian and had to re-evolve-, so there is virtually no coal on the East Coast of Australia from about 250-240Ma(ie from the Sydney-Bowen Basin-which royalties pays a reasonable proportion of East Coast academic salaries-you don't hear much appreciation though). Coal produced after 240Ma was from different plant species than previously, you also get a lot of red beds at this time indicating hothouse conditions. But my point is, all this took hundreds of thousands- to millions of years of vast amounts of c02 etc from Siberian Traps volcanism-oceans didnt,and probably won't, acidify quickly-ie less than tens of thousands of years?, if they do from humans at all.
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  36. @ 35 thingadonta A version of the naturalistic fallacy? Just because "Event A" happened under "natural conditions" over XXX Ma does not preclude it happening in the short term future. Accelerated release is not contingent upon causation being either "natural" or "human induced". What matters is the chemistry/physics. One would think the idea of positive feedback loops (release of the reserves of Co2 and CH4 when we reach the right "tipping point")) are crucial to understanding the issue.
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  37. Here we go, another log on the cheery fire of discussion: Increasing concentrations of carbon dioxide in sea water are driving a progressive acidification of the ocean1. Although the associated changes in the carbonate chemistry of surface and deep waters may adversely affect marine calcifying organisms2, 3, 4, current experiments do not always produce consistent results for a given species5. Ocean sediments record past biological responses to transient greenhouse warming and ocean acidification. During the Palaeocene–Eocene thermal maximum, for example, the biodiversity of benthic calcifying organisms decreased markedly6, 7, whereas extinctions of surface dwellers were very limited8, 9. Here we use the Earth system model GENIE-1 to simulate and compare directly past and present environmental changes in the marine realm. In our simulation of future ocean conditions, we find an undersaturation with respect to carbonate in the deep ocean that exceeds that experienced during the Palaeocene–Eocene thermal maximum and could endanger calcifying organisms. Furthermore, our simulations show higher rates of environmental change at the surface for the future than the Palaeocene–Eocene thermal maximum, which could potentially challenge the ability of plankton to adapt. Rate of ocean acidification the fastest in 65 million years Now mind you, the actual paper title is "Past constraints on the vulnerability of marine calcifiers to massive carbon dioxide release" but who am I to deny a blog titled "Desdemona Despair" its little bit of fun? Besides, the more punchy version is after all the title of the press release from U. of Bristol and "fastest in 65 million years" is after all the result. So paleo data, models, a sexy press release. What's a rejectionist not to like? ;-)
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  38. 31.cbrock What you think NewScientist choose to include that phrase themselves? Seems unlikely from a level headed publication, if true it's possibly worse given NS has more impact than a single scientist
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  39. #36, I think you are misinterpreting #35. Or maybe I am. It seems that #35 says that less total CO2 released, but released quickly over a short period of time, cannot have a similar impact as a lot of CO2 released over a longer time period. I believe this is wrong. To support my assertion I tried to look up a figure (I thought it was in Caldiera and Wickett 2005, but my search didn't find a free version of the full paper). My Google search took me to some other interesting stuff. I particularly like the powerpoint presentation (fifth down on the list) -- lots of references and lots of relevance to the discussion above. Go here. Similar but less stuff (and more explanation) is shown in this pdf. Of particular interest to me in the slide show is the information on other important factors (carbonate!). It would be a very long term project for me to study the all the references to permit me to make a good summary. Hopefully someone with more expertise will do it instead.
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  40. @ 39 I may have misinterpreted. Here is the para I focused on: "But my point is, all this took hundreds of thousands- to millions of years of vast amounts of c02 etc from Siberian Traps volcanism-oceans didn't,and probably won't, acidify quickly-ie less than tens of thousands of years?, if they do from humans at all." I read that to imply he/she questioned how human activity could result in acidification. He posits time periods and natural processes and contrasts (by implication) possible human interactions with the climate. That's how I read it. (see last sentence) It could be we are *both* reading the different things into the post because the argument is muddled and attempting to argue both points?
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  41. A few points: re 39 Steve L. "I think you are misinterpreting #35. Or maybe I am. It seems that #35 says that less total CO2 released, but released quickly over a short period of time, cannot have a similar impact as a lot of CO2 released over a longer time period. I believe this is wrong. " I am skeptical when you want to change an entire ocean's chemistry in less than tens of thousands of years, taking the geoligical record as a starting point. This is how long the geological record generally says it takes, even under extreme scenarios. So I dont know how pro AGW people use the past geological record to scare us abvout short human lifetimes. It's like a biologist scaring us about our rate of speciation. This is one of the main skeptic arguments -ie the time it takes to change the oceans, warm the planet etc etc (add it to the list), and is similar to the arguments in palaeontology and biology over gradual evolution versus punctuated equilibrium. That is, how fast is 'rapid/punctuated' versus 'gradual' when you are referring to geological time periods? It's a question of semantics really, eveyone agrees that the rate of evolution can change, but gradualists are very skeptical of any 'jumps' or 'jerks' or 'rapid' rate changes. (It also harks back to the days of the catastrophists and the uniformitarians in the 19th century -Darwin was a a uniformatirian and got it wrong with regards to 'mass extinction' events (he thought they were just gaps in the fossil record), Cuvier was a catastrophist- like nearly all pro-AGW people, and got it right with to mass extinction events). But as for mass extinctions, we are talking in most cases, of hundreds of thousands of years. Skeptics, therfore, contend that for somnething like ocean acidification by C02, it will take about that long to do it, which makes current humnan activities regarding ocean acidification, irrelevant. We can never release the kind of amount of gases that Siberian and Decaan Traps volcanism can do over several hundred thousand years in order to change ocean chemistry. Skeptics contend that various pro AGW researchers have vastly ignored and downplayed the time periods involved with most mass extiction events, and exagerated their own figures to scare people (like Jones with Siberian temperature data). Skeptics also contend that by the time the ocean acidifies (if it does at all, it is well buffered in many other respects in its interactions with volcanoes, sediments, Mid oceanic ridges etc etc?) from human c02, say in about 10,000++ years (?), we will have long ago given up our reliance on fossil fuels. (If this figure seems way too long, that is what is usually meant by 'geologically rapid', conveniently distorted by some coral reef researchers). As for K/T and #34, bolide impact pushed species over the edge after Decaan Traps volcanism had already weakened many ecosystems and which had begun several hundred thousand years earlier. Species were already in decline, especially marine species. This is well established. It was not one or the other (volcanism or bolide impact), it was both. re #32 The Chicxulub impact did not cause Decaan Traps volcanism, becuase it was already well underway (several hundred thousand years) before the asteriod/comet hit Mexico. Species were in decline already for about the previous few million years (including the dinosaurs-have a look at eg the "Walking With Dinosaurs" series-this is well established in peer reviewed literature, volcanic gases/effects were already killing the eg dinosaurs before they were pushed over the edge to oblivion by the asteroid. It was a one-two punch, which is why it was such a major extinction event). You can understand it this way, mass extinctions are by nature worse when a combination of factors are involved. There have been many large impacts in earth hoistory with no mass extinctions. re#36 "Accelerated release is not contingent upon causation being either "natural" or "human induced". What matters is the chemistry/physics. " What matters is the time periods involved. Mass extinction events take hundreds of thousands of years to change the chemistry of the oceans. Ask a volcanologist (which is one reason why Plimer is such a skeptic-one of his pet topics is volcanology-and he is more informed about what they do to oceans, as Veron is not). If someone wants to counter most of the above, they have to show how the past geological record shows the oceans can acidify in a few hundred years from changes in c02 levels. As far as I know, it says no such thing.
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  42. @ 41 Re KT/Cretaceous extinction: see my post @ 34 in which 2010 Science paper confirms Chicxulub as cause of dinosaur extinction here. Cite your references, not popular TV show. Re Deccan Trap theory the stress is on *may*: "Eventually, most paleontologists began to accept the idea that the mass extinctions at the end of the Cretaceous were largely or at least partly due to a massive Earth impact. However, even Walter Alvarez has acknowledged that there were other major changes on Earth even before the impact, such as a drop in sea level and massive volcanic eruptions that produced the Indian Deccan Traps, and these may have contributed to the extinctions." Your post: "So I don't know how pro AGW people use the past geological record to scare us about short human lifetimes. It's like a biologist scaring us about our rate of speciation..." ~ Actually, if we are talking about viruses then, yes speciation could be alarming. AIDS is a perfect example where it made the species jump from host it's chimpanzee population into the human population. The virus itself mutates with alarming frequency, thus developing many strains. Re using the geological record, to be frank the state of exobiology is such that we only have *one planet* in which to base our speculations on. As a consequence, it is perfectly reasonable to use the geological and paleontological record as a basis for drawing conclusions. Re Plimer, he is a geologist NOT a paleontologist or biologist. Just like his views on climate change, he is operating well outside his areas of expertise. As a consequence, his understanding of mass extinction events,their causes and the like are limited. Re you last comment: "What matters is the time periods involved" Again, I think my point about you falling into the naturalistic fallcy is correct. Ironically, you use the supposed length of time of extinction events to somehow prove your point but then chastise us "alarmists" for using the geological and paleontological data ourselves.
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  43. Anyone knowing about Plimer and his most recent error-strewn book, would not attempt to use him for any sort of back-up to an argument, even in fields he is supposedly expert in. His credibility is in shreds. As for the naturalistic fallacy, perhaps that should be added to the one that sees those in denial using past changes in climate as some sort of response to why humans can't possibly be changing the climate now - replied to by asking whether forest fires starting naturally in the period pre-man, means that man can't now start forest fires. Is that a logical fallacy ?
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  44. re: 41 "I am skeptical when you want to change an entire ocean's chemistry in less than tens of thousands of years" I don't think anyone's suggested that. The problem is a change in the acidity of the surface layer of the ocean, at a pace too rapid for it to be dispersed into the deep ocean.
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  45. Thingadonta, Your analyses are flawed. As already pointed out, the fact that some extinctions of the deep past occurred during (apparently) very long periods (100’s of 1000’s of years) doesn’t preclude the likelihood that very rapid perturbations of the climate system (on the 100’s of years time scale, or even less) can’t produce extinctions on much faster timescales. The end Cretaceous extinction is a case in point. It’s quite likely that this extinction was the result of a long environmental stress resulting from the massive flood basalt events that formed the Deccan Traps with a coup de grace resulting from the Yucatan impact into calcium carbonate and calcium sulphate-rich deposits. That extinction very rapidly wiped out all land animals bigger than a cat, and caused massive extinction of marine organisms. The marine extinctions were likely due to rather rapid acidification of ocean surface waters. There’s lots of evidence that supports this view (reviewed here and here[*], for example). Pretty much all marine species that inhabited the surface water columns and that fixed calcium carbonate disappeared likely due to rapid ocean acidification. As indicated in the top article, coral reefs disappeared (not to return for 2 million years). All plankton with calcium carbonate shells disappeared for ½ a million years. What strongly supports ocean acidification is the fact that diatoms that have silica shells didn’t disappear, and nor did some deep sea floor species that weren’t affected by sea surface acidification on timescales shorter than those required to dilute the acidification through the entire oceans. These extinctions were very fast. And acidification of the especially important and vulnerable top hundreds of metres of the oceans can occur rather quickly (Adam C just pointed that out). That’s been described in a recent review of evidence for ocean surface acidification (especially the consistent finding worldwide of a reduction of biogenic calcite in the spherule layers associated with deposits from the impact-se second link in paragraph above). Rapid release of CO2 on the hundreds of years timescale will cause acidification of the top hundreds of metres of the ocean on a similar timescale. In fact, it is the rapidity of release of acid-forming gases (CO2 and sulphurous oxides) that is especially dangerous for the oceans, and the reason that the end Cretaceous and Paleo Eocene Thermal Maximum are significant analogues for today’s massive and extraordinarily rapid release of greenhouse gases. The very slow release of CO2 right through the Cretaceous with the resulting greenhouse warming drove the carbon cycle around twice as fast as today with the result that there was an extraordinary richness of calcerous marine animals (the “Cretaceous” is named after chalk – latin “creta” for that reason). But when greenhouse gases and sulphurous acids entered the atmosphere very rapidly, so the ocean extinctions resulting from rapid ocean acidification followed. This is all pretty obvious I think. After all, we know that since around 1970 we’ve lost around 19% of coral reefs and around 35% of the remainder are threatened. We have good evidence that there are relatively recent occurrences, since we can observe since the 1970’s the widespread bleaching of long lived (600 year old) coral species. So far the dominant effect has been temperature since the major pulses of coral bleaching and die-off is occurring during the El Nino episodes riding on the background rise in ocean surface temperatures. However we’re getting pretty close to the CO2 levels where many of the carbonate-fixing species simply won’t be able to produce their skeletons. That’s also described in a recent review by Veron and a large number of well-informed scientists. [*] can’t find an on-line pdf of this one.
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  46. Sorry to be redundant but here again is the link to the Veron paper John discusses: Mass extinctions and ocean acidification: biological constraints on geological dilemmas I bring it up again because the paper covers a tremendous amount of previous research, addresses most of the concerns about past events mentioned in the thread of discussion so far.
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  47. Ty doug for reminder, well worth re-reading.
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  48. And at Chris post 45 - nice summary indeed.
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  49. We should worry about CO2 level in the sea, but for the right reasons. As marine life, for physiological reasons, are more sensitive to (even small) changes in CO2 concentration than terrestrial life then it is something we should be considered about (at least those of use that likes to eat sea food.) However, I do not think we need to worry for anoxia to appear on a global level (i.e. kill a majority of all marine life) the atmosphere would need to be depleted of oxygen for this to happen, but fortunately this is not a very likely scenario in the near future (but will eventually happen when the sun turns into a red giant - then we can talk about real global warming, however any acidification of the sea’s at that time will become a minor problem by then ;). About the plausible theory that CO2 can cause mass extinction. It can not be excluded that elevated levels of CO2 in the past has been a consequence of a previous mass extinction: In the conclusion of "Global biodiversity and the ancient carbon cycle (Rothman)" we can read: "we find that the correlations express complementary fluctuations in the size of the organic and inorganic carbon reservoirs within the biosphere, atmosphere, and hydrosphere. Consequently, CO2 levels decreased as biodiversity increased. These conclusions imply that fluctuations of CO2 levels have been driven primarily by changes within the biosphere and only secondarily by purely geologic and geophysical processes." Some final food for thoughts here: Consider Rothman’s paper, then we may postulate a hypothesis that the current increasing of atmospheric CO2 concentration is a consequence of an current ongoing - for some reasons - (mass) extinction.
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  50. #49 batsvensson Thanks for pointing out the Rothman paper; it's interesting. I should note that also in Rothman's conclusion is a disclaimer, "Indeed, our analysis leaves open the possibility, for example, that tectonically induced reductions of CO2 levels led to increased diversity in both continental and marine ecosystems. A definitive statement of causation will require further work that includes not only the study of other geochemical signals (10) but also improved paleontological records." This is frequently one of the problems with (necessarily temporally coarse) ancient paleo data--the resolution is not always there to make a strong causal determination. One then has to look at the physics and known biogeochemistry to evaluate one hypothesis vs. another.
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