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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 51 to 71 out of 71:

  1. batsvensson at 07:56 AM on 17 April, 2010 (i) anoxia certainly doesn't require the atmosphere to be depleted of oxygen. Anoxic ocean events in the deep past seem to have resulted from elements of greenhouse-induced warming, temporary cessation of deep ocean circulation and ocean stratification. Try this (not very well written) Wikipedia page on anoxia (ii) we know the reason for the current increasing atmospheric CO2. It's not due to a "current ongoing (mass) extinction"!
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  2. #45 Chris: The extinctions you refer to are not 'rapid' (KT/ POTM). They occur over tens of thousands or years+. This is the main issue, and why papers such as Veron are wrong/misleading. Verons article on 'coral reef crisis' is an exercise in exageration. Have a look at his language designed to produce the greatest exageration possible: "degraded water-quality and increased severe weather events." Both not true. Severe weather has not increased. When reefs are impacted by severe weather, they always recover, you would think they have evolved to, after millions of years of 'severe weather'. Opportunistc species rebuild them, as in after volcanic eruptions in the Pacific, Krakatoa etc. "other environmental impacts." ie if you run out of enough 'disaster' words, just say 'other environmental impacts', that way you don't have to explain it. "Perhaps most importantly, there is no evidence that reefs have ever experienced true parallels to today’s anthropogenically-driven combination of stressors." Baloney. End Permian, end K/T, POTM. All 3 took tens of thousands of years. All 3 worse than now. Veron wants us to believe that puny humans can outbeat the Siberian Traps several hundred thousand years of explosive volcanism. His statement that we have lost 19% of reef since 1970 is a gross distortion. (We should get Macintyre and Lomborg onto these coral reef exagerators). What's more, if temperatures have risen, this promotes coral reef growth at the margins of their range: eg Southern Barrier reef etc, I know this partly becuase I studied this area and this issue in my honours thesis. Nowhere does he mention that the ocean has buffering mechanisms which cannot be easily reproduced in the laboratory, and which make oceans VERY resistant to rapid chemical change, as the geological record shows (which is why it takes tens of thousands of years to change them and for marine species to go extinct in geological time periods). Veron completely ignores this, because it is in his interest to promote as much 'quick catastrophism' as possible. Mass coral bleachings are a natural event that occured before the 1970s, there is 'little record of it' before this because no one was looking. Communities in the Pacific have recorded it for hundreds/thousands of years. "The 1997/1998 mass bleaching event killed approximately 16% of coral communities globally (Berkelmans and Oliver, 1999; Wilkinson, 2004). It was also the start of a decline from which there has been no significant long-term recovery." Incorrect, corals are used to such events, it occurs seasonally all the time including at the margin of their range, and they get over it all the time, Veron does not. The article link by Caldera shows he doens't know much about the K/T exinction. He doesnt even mention the delcine of marine organisms from well before Chicxulub about 70Ma. He doesnt mention the Decaan Traps either, and yet this were the major cause of the maine extinctdions (not the impact), the bolide impact was too short to produce long lasting marine effects. He also mentions that the earth was warmer in the Cretaceous because volanoes were spewing out more c02. But I thought volcanic c02 was so minor as to be irrelevant? So it's only important when convenient. IE Volcanoes can change climate on long time scales, but not short ones, humans can change climate on short time scales, but they cant take a geological long time to do it, even though volcanoes have to. (Somebody tell the volcanos because they arent listening). If Veron and co. are the measure of 'well informed scientists' regarding the next announcement of impending doom, then I don't think we have much to worry about.
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  3. You’re still making fundamental errors of logic thingadonta Volcanoes during the Cretaceous. Eruptive tectonic activity (volcanoes; igneous province eruptions etc.) were active during much of the Cretaceous at a level that resulted in raised greenhouse gas warming and an increase in the carbon cycle at a rate around double that of present. The fact that volcanic/tectonic activity makes no significant contribution to raised greenhouse levels now, but did then isn’t a difficult concept to grasp! Volcanos/tectonic activity isn’t “only important when it’s convenient”; the activity is important when it’s important, and unimiportant when it’s unimportant. We live in a contingent world where things change, and thus events and contributions are different at different times in Earth history. If we’re considering the effects of raised greenhouse gas levels (and sulphurous oxides) on global temperature and ocean acidification, then that’s the essential point and we can’t make categorical statements about what volcanoes, or people or impacts can or can’t do, and then ignore the evidence. Anything that raises greenhouse gas/sulphurous oxide levels quickly will cause rapid warming, and rapid ocean acidification. That seems to be what happens at the KT boundary, and the evidence indicates rapid ocean acidification and rapid extinctions. Likewise greenhouse gas levels are rising rapidly now, temperatures are rising rapidly and ocean acidification is increasing rapidly. The fact that many of the extinctions in the deep past seemingly occurred as a result of processes happening over long periods, doesn’t preclude the likelihood that processes that act quickly (bolide-induced vaporization of calcium carbonate and sulphate deposits; massive, rapid oxidation of long-sequestered fossil fuels), may result in rather rapid extinctions. The end Cretaceous informs us of that (see refs. in my post #45; the lesser PETM extinctions are another example). Ocean buffering mechanisms. The major ocean buffering mechanisms are (i) the very slow ocean circulations that dilute the effects of local perturbations on the 100’s to 1000 year timescale; (ii) the carbonic acid-bicarbonate-carbonate equilibrium that acts to maintain the pH of the oceans. While this makes the oceans resistant to change in pH, it doesn’t make it impervious to change, and in fact we know that rapid increase in CO2 levels (and perhaps massive vaporization of sulphates such as likely occurred at the KT impact), can overwhelm the buffering capacity of the oceans, particularly the important surface regions (upper several hundreds of metres). Since we have strong evidence that this occurred rather quickly following the KT impact (see papers linked in my post #45), and can measure the acidification of the oceans in the real world, we can hardly base our views on a mantra that “it takes tens of thousands of years to change them”. A very rapid increase in the surface absorption of atmospheric acids can overwhelm both the chemical buffering and the ocean circulation contributions to buffering. Again, when things change slowly they change slowly; when they change quickly they change quickly! There are no set rules. Incidentally many relevant elements of ocean buffering can be rather easily transferred to the lab. The H2CO2 = HCO3- + H+ = CO3-- + H+ equilibrium is straightforward and well understood, including its response to acidification. Lkewise the aragonite saturation that is crucial for shell and skeleton formation by many marine organisms is rather well understood and can be transferred to the lab. There’s a huge scientific literature on this (see for example papers in a recent issue of Oceanography recent issue of Oceanography , and refs in/cites of this). Coral bleaching. To assert that “corals get over it all the time” and referring to “seasonality”, is not relevant. We’re not considering variations (especially temperature and pH) within a range to which populations are adapted. We’re considering very rapid persistent trends (in sea temperature and acidity) towards regimes to which corals are poorly adapted. Real world observations indicates corals are increasingly unable to “get over it”.
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  4. @ Chris #51 1. I am not aware of any known process that suggest that the oceanic circulations are going to stop even slow down. Are you? 2. I wrote "hypothesis", not "theory".
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  5. batsvensson, I was addressing your assertion that: "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." and pointing out that the atmosphere doesn't need to be depleted of oxygen for this (anoxia) to happen. Not sure what your point about "anoxia" refers to anyway. The main environmental stressors for coral morbidity/mortality are warming and ocean acidification, both of which are happening and likely to be increasingly problematic in the coming decades. As for your "hypothesis"; why would we propose or consider a hypothesis for which there is not only zero evidence, but which is robustly contradicted by what we know of the real world? I don't see how it takes us anywhere scientifically speaking...
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  6. chris, 1. It is referring to the OP. Anyway, should I understand your comment that you believe it is a possibility that within, say, the next hundred year all of live in the seas may be dead? 2. What make you believe there is "zero evidence" and that this is "contradicted by what we know"?
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  7. batsvensson, 1. I can't see where your interpretation comes from. I'd say we can be fairly sure that with current emission scenarios, in 100 years the world's corals will largely be degrading relics, and marine organisms requiring aragonite saturation for creating shells and skeletons will be in decline. You'll have to consult an expert or look more deeply into the science to get a feeling for the knock-on consequences of these effects. But the seas obviously won't be "dead"! 2. There's zero evidence that the current increase in atmospheric [CO2] is a response to some unidentified mass extinction. Can you supply some? It's your notion, so it's really up to you...(and please outline the mechanism underlying your hypothesis). The notion is contradicted by the facts that: (i) The profile of atmospheric [CO2] increase is matched by the known emissions, and can be accounted for by quantitative analysis of our cumulative emissions (ii) The terrestrial environment has absorbed about 10% of our emissions as a result of slightly enhanced pimary production. This is incompatible with a terrestrial mass extinction, which, in any case, we know hasn't happened, even if there have been some species extinctions and many stressed environments. (iii) The isotopic signature of enhanced atmospheric [CO2] (greatly decreasing 13C/12C ratio, and decreasing 14C/12C ratio at least during the period to 1954, when nuclear testing has complicatd the analysis), indicates that enhanced atmospheric [CO2] has come from a fossil fuel source. (iv) The high resolution atmospheric [CO2] record shows that atmospheric [CO2] has been rather steady during (at least) the 1000 years up to around the mid 19th century. There is no evidence for a "mass extinction" starting in the mid-19th century (and the rise in atmospheric [CO2] levels match human emissions from around that time). ...etc. etc.
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  8. As for the volcanic CO2, that should also be put in context. Currently, anthropogenic emissions are approximately 150 times larger than volcanic. So, from the CO2 change point of view, we are mimicking periods when volcanic activity was 150 times greater than now. To be honest, I don't really know how it would compare to the Dekkan traps or Siberian traps but that would still be rather impressive. I don't know what kind of oceanic "high resistance to pH change" it would take for that to go unnoticed.
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  9. Chris, 1. What percentage of the marine genera would the example constitutes? 2. It is unclear to me how (i), (ii), (iv) contradicting what I wrote. (iii), yes possible.
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  10. batsvensson, you need to: 1. look at the numerous papers I and others have linked to; 2. explain the mechanism that underlies your hypothesis. Answering with coy questions and vague statements that don't address straightforward points is getting close to trolling behaviour. It's pretty straightforward. I'm directly addressing your statement: "...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." So give us a scenario that describes a mechanism underlying your hypothesis that is consistent with my points (i) to (iv) in my post just above. Then we can clarify whether my points contradict your hypothesis. Otherwise I could, just like you, propose a hypothesis (let's say that "increased atmospheric CO2 levels result from animals breathing"), and when you gave me some reasons why that hypothesis is inconsistent with what we know, I could reply as you did "it's unclear to me how your points contradict what I wrote".....and we'd similarly be no further forward!
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  11. I haven't read through all the way up to here -- I'm still catching up. This comment is a thanks to HR @16 for this paper by Manzello about Eastern Tropical Pacific coral reefs -- given BP's comments at the Ocean acidification (evil twin) thread , I think he would also find it very enlightening. Galapagos reefs are chronically exposed to lower pH (and aragonite-undersaturated) water due to upwelling and therefore their structures are poorly cemented and they are more vulnerable to erosion. I would infer that it is also more difficult for them to recover following high temperature events (El Niño), despite their evolutionary history in these conditions since approximately the close of the Panamanian isthmus. Manzello cites Manzello et al 2008, which adds that upwelling nutrients may stimulate bioerosion. The Manzello (but not Manzello et al) paper cites Veron 2008 briefly in the discussion and concludes that the mechanism discussed fits with Veron's hypothesis that reef gaps are driven by ocean acidification.
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  12. Chris, I am interested to know why you reject the idea, therefore my questions. If you don’t like to answer my questions then that is fine with me, but to me and this is based on what I know and scenarios I can imagine what you list seams not to contradict it and I gave you a second chance to rethink it but maybe what you claims does make sense to you, then that is fine with me as well.
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  13. Thanks for this, fascinating stuff, especially Chris #45. I have a question for nobody in particular: Hansen says that burning all the coal and tar sands will lead to Venus. BAU projections call for 5-7C temps in 2100, which is deadly, but not Venus. Does this mean that feedbacks at 5-7C will subsequenstly overwhelm the planet, since the rise in CO2 has been so rapid?
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  14. batsvensson at 05:15 AM on 19 April, 2010 batsvensson, I told you in detail why I reject your idea. If you don't agree, you really need to say why! If you can "imagine" "scenarios" "which (my) list seams not to contradict", you really need to tell us what these scenarios are. We can hardly be expected to address ideas that are in your "imagination", that you don't tell us about. We aren't mind-readers!
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  15. Chris @ 07:11 AM on 24 April, 2010, A general assumption in science is: if it isnt forbidden then it may be possible. As far as I know nothing stated in the idea is forbidden. However you say the idea is contradicted, fair enough. However contradicting is not the same as forbidding. Anyhow, if this was all about trying to convince you, or anyone else for that matter, about some certain likelihood to take this idea serious then indeed would "need to say why". Besides the point; is it really impossible for you (you have no ground to refer to "we" above) to imagine a scenario in which the idea is not contradicted?
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  16. The back-and-forth between batsvennson and chris in this thread might be a bit confusing for anyone who hasn't followed it closely. Back on the first page of comments, batsvennson wrote: [...] 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. This seems very peculiar to me. We know that we're adding CO2 to the atmosphere from combustion of fossil fuels, land use, and other factors. So the increase in CO2 in the atmosphere isn't a mystery. Batsvensson's hypothesis would necessitate some unknown mechanism removing anthropogenic CO2 from the atmosphere and some other unknown mechanism adding CO2 due to an ongoing mass extinction. (There is plenty of evidence that we are in the midst of a new mass extinction, caused by human impacts on the biosphere, but no evidence that this inherently is causing a large CO2 flux.) Occam's razor suggests that an explanation with zero unknown processes is preferable to one that requires two different unknown processes. So, Chris understandably points out (in this comment) that batsvensson's hypothesis is probably not a productive line of scientific inquiry: As for your "hypothesis"; why would we propose or consider a hypothesis for which there is not only zero evidence, but which is robustly contradicted by what we know of the real world? I don't see how it takes us anywhere scientifically speaking... batsvennson then asks Chris for more elaboration on these objections, and Chris obliges in this comment. There is some subsequent back-and-forth, ending with this very strange statement by batsvennson. Not all hypotheses are created equal. On the subject of the increasing CO2 concentration in the atmosphere, consider the following two hypotheses: H1: The increase is primarily due to combustion of fossil fuels. H2: The increase is primarily due to invisible leprechauns. I think most people would agree that the former is more productive than the latter, not just because it's more realistic but because it's testable. A hypothesis that is stated in vague, ill-defined terms, or that requires unknown and unexplained phenomena, is not really testable and thus is not particularly useful. Here's another case: H1: The increase is primarily due to combustion of fossil fuels. H3: The increase is due to the rapid deterioration of an undiscovered lens of frozen CO2 (dry ice) buried beneath the topsoil of a remote region of the Himalayan plateau. Now, unlike the leprechaun hypothesis, H3 is actually testable -- NSF or its European or Chinese equivalents could fund a field campaign to travel to Tibet and look for this interesting dry-ice feature. However, it's unlikely that a grant proposal focused on this hypothesis would be funded. Why? Because there's no prior evidence or reasoning to suggest that it's even remotely likely. A hypothesis with no justification for its own existence is better than an untestable hypothesis, but not much. Moving on, consider the next two hypotheses: H1: The increase is primarily due to combustion of fossil fuels. H4: The increase is primarily due to outgassing of CO2 from the oceans as they are warmed by a cyclical increase in solar irradiance. Now, H4 is clearly better than the leprechaun or dry-ice hypotheses -- it is testable, and it is at least based on plausible physics and some things we know about the relationship between temperature and the partial pressure of gases in seawater. But it still has problems -- in particular, it conflicts with other things we already know about the Earth system (solar irradiance has been decreasing, CO2 concentration in surface waters is increasing as CO2 moves from the atmosphere to the ocean rather than vice versa). In addition, H4 still requires some unknown explanation for why the CO2 that we know we're emitting from our cars and power plants is somehow not contributing to the atmospheric store of CO2. Now, batsvennson's hypothesis suffers from the problems of H3 and H4 above. She/he doesn't present any evidence to justify why we should even bother to consider "an ongoing mass extinction" as an explanation for the current rise in CO2, aside from one brief reference to a paper that suggests that some mass extinctions in the geologic past may have caused an increase in the CO2 flux from the biosphere to the atmosphere (but where's the evidence that's happening today?) More importantly, however, it is contradicted by the changing isotopic signature of atmospheric carbon. Finally, from a straightforward logical perspective it requires throwing out a much simpler explanation (we know we're producing CO2 from fossil fuels) in favor of a more complex one. As Carl Sagan said, extraordinary claims require extraordinary evidence. The claim that "something other than combustion of fossil fuels is responsible for the current rise in CO2" is most definitely an extraordinary claim. It's up to anyone proposing such a claim to provide extraordinarily convincing evidence. So far, batsvennson has provided no evidence at all.
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  17. Mike Roddy writes: Thanks for this, fascinating stuff, especially Chris #45. I have a question for nobody in particular: Hansen says that burning all the coal and tar sands will lead to Venus. BAU projections call for 5-7C temps in 2100, which is deadly, but not Venus. Does this mean that feedbacks at 5-7C will subsequenstly overwhelm the planet, since the rise in CO2 has been so rapid? Good questions. First of all, note that this is Hansen's own opinion, and other scientists may not be convinced by this claim. That said, Hansen is talking about burning all the conventional oil, coal, heavy oil/tar sands (cf Canada, Venezuela) and I think oil shale as well. That's a long-term, multi-century process, not something that would happen by 2100. So even if temperatures rise 5-7 C by 2100, Hansen's not saying that in itself would trigger a runaway greenhouse effect (RGHE?) like on Venus. What he IS saying is that if we spend the next few centuries burning everything, with CO2 over 1000 ppm, various other feedbacks like clathrates etc. would kick in and lead to RGHE conditions. That's still a pretty extreme claim, and I would want to see a bunch of convincing model results before accepting that it's possible. All that said, there's a lot of room for "extreme misery" even if we don't actually trigger a Venus-style RGHE. Burning a large enough fraction of coal and/or tar sands would put us at 3XCO2 and probably lead to disastrous conditions for much of the world's population.
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  18. There appears to be a desperate need to tie CO2 to the GW litany. To this end, this link has taken the reader far back in time to the Ordovician to draw a correlation between rises in CO2 and mass extinctions. This is beyond the pale of ludicrous as the comments discuss the rise and fall of corals, reefs and the insidious scourge of CO2. 1)Ancient reefs 560 mya were primarily cyanobacteria which trapped sediment and secreted calcium carbonate, forming large structures (up to 450m thick, but more usually less than 5m thick) known as stromatolites. 2)The first scleractinians, or modern day hard corals, turned up during the Triassic period about 230 mya 3)Coral reefs were almost replaced by bivalve reefs in the early Cretaceous period - rudist bivalve reefs dominated corals for around 30 million years. 4)Changes in the configuration of the continents limited or expanded coastal shelves influencing reef growth 5)Volcanism and plate tectonics have resurfaced the earth 6)The reefs divers are most familiar with are only 10,000 years old 7)When looking at the fragility of reef systems and the oceans biomass natural and man-made hazards have impacted their growth and health but NOT FROM CO2. The geologic record in many cases is quite explicit. When anyone tries to draw vague parallels to climate changes associated with wandering land masses and global conditions alien to those of today, it only reinforces the skeptic’s position. When I was a kid I made a very detailed model of a Werewolf. It was painstakingly painted and dramatically presented. In the end it was a beautiful model of a fictitious creature. It too was art not science.
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  19. #68: "this link has taken the reader far back in time to the Ordovician to draw a correlation between rises in CO2 and mass extinctions. " No, you've missed the point. That 'CO2 levels were higher in the past' (all the way back to the Ordovician) is a denier argument. This argument requires that one make direct comparisons between the distant geologic past and today based solely on reconstructed atmospheric CO2 -- and that is what stimulated the discussion of plate tectonics, ocean circulation, completely different fauna, etc. However, this does nothing to negate the current CO2-climate issue. That's been discussed on many other threads here. I don't recall anyone here claiming that CO2 is an "insidious scourge", but if you have some new insight as to why it is not a significant climatologic concern, please be specific in your argument. "When anyone tries to draw vague parallels to climate changes associated with wandering land masses and global conditions alien to those of today, it only reinforces the skeptic’s position. " Once again, trying to draw those parallels is exactly the skeptic position -- and you point out quite elegantly just how ludicrous that position is.
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  20. Geologista@68: Chances are you are long gone, and may not respond but just in case you may actually get word of this...this "geologita" would like you to provide definitive support, in the form of peer-reviewed sources, that back up your *highly* dogmatic assertion. "7)When looking at the fragility of reef systems and the oceans biomass natural and man-made hazards have impacted their growth and health but NOT FROM CO2." I will be astonished when/if you do/can.
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    Moderator Response: [DB] Geologista has indeed not commented here since.
  21. A New Understanding When I was 28, in 1971, I developed a theory on the evolution of animal life, nothing that would go against Darwin’s Theory of Evolution, but it could explain the environment in which evolutionary changes would take place. The theory is this - if the partial pressure (pp) of carbon dioxide is above a certain level, at least that partial pressure of the gas is found in animal tissue and that puts a limit on the metabolic rate possible. Any lowering of the CO2pp allows greater quantities of tissue-produced CO2 to be removed from the cell, hence an increase in pH of the cell environment. This change allows a slightly higher metabolic rate to be accommodated in the animal and within a short period of time genetic modification results in a different genotype to appear thanks to epigenetic changes. Epigenetic theory is the key to my theory that movements in the partial pressure of CO2 either reduction = greater metabolic possibilities, or increase = disaster for the phenotype, either directly or via the genotype, through inheritance. Any increase in the level of CO2 at the resting state results in a lower pH. If that happens then modification to tissue occurs through epigenetic changes, a fairly new understanding of sets of switches within a gene sequence that can be reversed to alter the expression of the gene from the expected to an undifferentiated cell, cancer being the most common result. The Development of Life on Our Planet The Lag Phase A cosmic event about 2.5 billion years ago deposited large quantities of genetic material onto our planet. The full expression of that genetic material took a very long time, starting with single photosynthesizing cells, through oxygen utilising single cells to multi-cell creatures which became visible in the geological record about half a billion years ago as undifferentiated calcium agglomerations. This was probably the first direct evidence of both animal life and a major reduction in CO2pp. These creatures had been using calcium as part of the mechanism for removing CO2 from their tissue. Calcium, as a cation, combines with CO2 and a bit of oxygen to form calcium carbonate, a solid particle the animal could manipulate to the margin of its tissue, where it fell away to form limestone or chalk. This simple mechanism helped photosynthesizing cells in reducing the CO2pp even further until the CO2 was low enough to permit the speeding up of the generation of CO2 within its tissue and thus calcium carbonate to such an extent that the mechanism for its removal was overwhelmed, the animal dying because it became choked by its own waste product. Many strange calcium carbonate remains are seen in the Cambrian strata. However, it was not long before the deposition of this material came under genetic control to provide either defence or attack structures on the animals, we also see their remains a very short time after in the same strata. The Log Phase This very important point in the geological record marks the end of one phase in the chemical reaction called Life on Earth and the beginning of another, the end of the lag phase, where chemical change is slow and the beginning of the log phase where chemical change is rapid. The geological record shows a rapid reduction in CO2 via the deposition of vast amounts of carbon over a very short period of (geological) time compared to its rate of deposit during the lag phase. Accompanying this deposition of carbon there is a consequential increase in the metabolic rate of life as expressed in life forms that become larger, more complex and faster in water, on land and also in the air. Not all animals took advantage of these new possibilities and as a result, they were taken advantage of by those that had. A quick look at the various life forms ranging from fish to birds mapped against the deposition of carbon confirms the linkage – removal of carbon, in the form of CO2, from the atmosphere – increase in metabolic rate – increase in utilization of that metabolic rate by important changes in animal form and capability. Sadly, not all the animals that lived on the crest of the development curve of metabolic rate are with us today. Remember the word, “epigenetic”, that word is the key to the development of this vast array of life forms. As the pH increased, more switches were moved and more adaptions made, some successful in the sense that they were able to survive and pass on their genes, others would fail to do so. Those that did survive went on to make the most of their metabolic rate, either in terms of size, speed or internal heat generation or in some cases in combinations of two or three of these effects. Life at the leading edge of the development curve was always in the best position to exploit all other life forms. However, such life was also the most exposed, especially for those which had taken on all three of the effects of increased metabolic rate, size, speed and internal heat generation, should the partial pressure of CO2 go into reverse by increasing to a level greater than when their metabolic rate had come into being. The lowering of the pH following such an event would cause epigenetic switches to throw and loss of differentiation would follow. It matters not what the cause of the increase in CO2 turns out to have been, as long as the boost was great enough to take its pp back to a level that was present before the level of the metabolic rate with which the animal was born. In such a circumstance Life’s development curve stopped and effectively dipped to a lower level. Life effectively went into reverse with the highest metabolic rates no longer supported. In terms of geological time, such events take up very little space on the horizontal scale, even if the effect of the reversal is massive in terms of the number of species wiped out. Therefore, such reversals would look like minor ripples on the curve. The development of animal life would soon get back on track when the boost of CO2 had been absorbed by plant life. Animal life produced even more forms to take advantage of the possibilities offered by reductions in CO2pp. This cycle of increase in metabolic rate and a subsequent reversal happened many times in the geological record but thanks to plant life being there to remove more and more CO2, Life continued to follow the log phase of the development curve. Until the advent of Man. This animal first removes vast swathes of CO2 sinks, trees and other green foliage. Then having found industrial uses for fire digs up coal, the main fuel for his endeavours, then extracts oil and gas to make his endeavours run smother and better. He is responsible for putting more CO2 into the atmosphere in the last couple of thousand years than anything else – this, along with the diminishing ability of plant life to restore the CO2pp to what is safe for its own existence is bringing the planet to a disaster. There are many epigenetic switches being thrown that resulting in more and more genetic disorders happening to all animal life – remember those animals at the leading edge of the log phase of the development curve of Life on Earth, well they are once again being hit by the increase in CO2pp. In our species, we see rapid increases, year by year, of the numbers of cancer cases, why? Because their scientific advisors tell our politicians that global warming, just global warming is the biggest problem we face from increasing CO2 in our atmosphere –WRONG! You know the biggest problem faced by the planet is the extinction of multiple layers of life thanks to increased CO2pp. There is no doubt about it, the development curve of Life on this Planet is about to plateau and possibly move to a termination trajectory. Is it already too late? Possibly, even probably, because it will take too long to achieve what really needs to be achieved – reducing CO2pp to pre-industrialisation levels once again. Bolandista
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  22. Bolandista, the only problem with your hypothesis is that there is no evidence to support it. If small shifts in CO2 levels caused major metabolic changes, or cancer, then it would have been spotted long ago. Can you point to any research to back up your ideas? You are also lacking evidence that life arrived on earth 2.5 billion years ago in a "cosmic event". There is evidence that life was around at least a billion years before that.
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  23. Vonnegut, why did you post the comment from Goreau if not to suggest something?  Why did you think SkS readers would find it interesting?  Why did you pick that particular quote from all of Goreau's comments in the thread?  There comes a time when one no longer receives the benefit of the doubt, even from the most generous. 

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  24. "Eruptive tectonic activity (volcanoes; igneous province eruptions etc.) were active during much of the Cretaceous at a level that resulted in raised greenhouse gas warming and an increase in the carbon cycle at a rate around double that of present."

    Alright, I'm confused.  If the Cretaceous had carbon cycle increases at a rate double of the present, that means that volcanoes were putting out twice what's being put out today at any given time, right?  So if that's true, how can we cause a faster acidification of the oceans when we are putting out less carbon per year than those volcanoes?

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    Moderator Response:

    [RH] Please note that we would prefer people not use all caps for emphasis, as it tends to read like shouting. Please use the bold or italics tools at the top of the comment box to add emphasis. Also, make sure you read the commenting guidelines.

    All caps changed to bold.

  25. Sorry, I'm used to forums where I don't have bold/italics options.  I will use those in the future here.

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  26. Varika...  The comment you're responding to here is discussing the difference between tectonic and volcanic emissions in the Cretaceous to tectonic and volcanic emissions now, excluding human emissions.

    Man-made emissions of CO2 are about 100X that of natural sources.

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  27. The science is settled:  It's Not Volcanoes.

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  28. Varika

    I second what Rob has said. The reference is to changes in tectonic CO2 emissions and a doubling during the Cretaceous of that tectonic rate. Human emissions are much larger than either rate - the US Geological Survey's estimate is that human CO2 emissions are 130 times total volcanic sources. Where elevated tectonic emissions can matter is when they go on for millenia and longer. Even the eruption of a super volcano such as Toba or Yellowstone is thought to only put the equivalent of 1/2 of human emissions into the air, and only for the duration of the eruption.

    This is the record of CO2 in the atmosphere from the Mauna Loa observatory:

    We might just barely see a wiggle on the annual mean line (black) around the time of the 1992 eruption ofMt Pinatubo if we squint hard and wish a lot. No sign of wiggles around the times of the eruptions of Mt El Chichon in 1982 and Mt Agung in 1964. Those were the big 3 eruptions during the period of the record. Far bigger than volcanic emissions but essentially an annual cycle is the absorption then release again of CO2 by deciduous plants (the wiggles in the red line). We can actully see the forests of the Northern Hemisphere going through their seasonal cycle.

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  29. Varika - note too that the sustained high levels of atmospheric CO2, due to this volanic outgassing over geological time scales, would have greatly increased the chemical weathering of rocks at Earth's surface mainly because of the intensified water cycle - more rain washing dissolved inorganic carbon (carbonate & bicarbonate ions in particular) back to the ocean.

    Over time this overcompensated for the loss of carbonate ions, and the oceans were actually more conducive to shell formation than they are today, despite the lower than present pH (acidification). This why the Cretaceous (meaning chalk) Period was so favourable to marine calcification.

    This doesn't occur with geologically-abrupt increases in atmospheric CO2, pH and carbonate mineral saturation state decline in tandem making seawater corrosive because the rate of weathering is far too slow to provide bicarbonate and carbonate ions back to the ocean. The weathering feedback which counteracts corrosive oceans can take over a hundred thousand years to respond sufficiently.

    Hope this helps clear up this apparent paradox. SkS will have a rebuttal on this topic soon.

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