Arguments
Does high levels of CO2 in the past contradict the warming effect of CO2?
The skeptic argument...
CO2 was higher in the past
"The killer proof that CO2 does not drive climate is to be found during the Ordovician- Silurian and the Jurassic-Cretaceous periods when CO2 levels were greater than 4000 ppmv (parts per million by volume) and about 2000 ppmv respectively. If the IPCC theory is correct there should have been runaway greenhouse induced global warming during these periods but instead there was glaciation."
(The Lavoisier Group)
What the science says...
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| The Ordovician glaciation was a brief excursion to coldness during an otherwise warm era, due to a coincidence of conditions. It is completely consistent with climate science. | |||||
Geologists refer to ancient ice-cap formations and ice-ages as "glaciations." One such glaciation that occurred during the Late Ordovician era, some 444 million years ago has captured the attention of climate scientists and skeptics alike. To get some perspective on timing, that's just over 200 million years before dinosaurs began to roam the Earth.
Unlike other glaciations in the last 500 million years, this one was exceptionally brief (lasting perhaps only a million years or so) but the main reason for generating so much interest recently is because it took place when CO2 levels were apparently sky-high. As Ian Plimer notes in his book, "Heaven and Earth", pp165:
"The proof that CO2 does not drive climate is shown by previous glaciations...If the popular catastrophist view is accepted, then there should have been a runaway greenhouse when CO2 was more than 4000 ppmv. Instead there was glaciation. Clearly a high atmospheric CO2 does not drive global warming and there is no correlation between global temperature and atmospheric CO2."
On the surface, Plimer does seem to have a point: if ice-caps managed to exist back then in an ultra-high CO2 environment, why are the vast majority of climate scientists worrying so much about keeping CO2 levels piddlingly low?
To answer this, we have to fill in some parts of the puzzle that are missing. Let's start with the CO2.
Plimer's stated value of 4000 ppmv or greater is taken from Robert Berner's GEOCARB, a well-known geochemical model of ancient CO2. As the Ordovician was so long ago, there are huge uncertainties for that time period (according to the model, CO2 was between an incredible 2400 and 9000 ppmv.) Crucially, GEOCARB has a 10 million year timestep, leading Berner to explicitly advise against using his model to estimate Late Ordovician CO2 levels due its inability to account for short-term CO2 fluctuations. He noted that "exact values of CO2... should not be taken literally."
What about evidence for any of these short-term CO2 fluctuations? Recent research has uncovered evidence for lower ocean temperatures during the Ordovician than previously thought, creating ideal conditions for a huge spurt in marine biodiversity and correspondingly large drawdown of CO2 from the atmosphere through carbon burial in the ocean. A period of mountain-building was also underway (the so-called Taconic orogeny) increasing the amount of rock weathering taking place and subsequently lowering CO2 levels even further. The evidence is definitely there for a short-term disruption of the carbon cycle.
Another important factor is the sun. During the Ordovician, it would have been several percent dimmer according to established nuclear models of main sequence stars. Surprisingly, this raises the CO2 threshold for glaciation to a staggering 3000 ppmv or so. This also explains (along with the logarithmic forcing effect of CO2) why a runaway greenhouse didn't occur: with a dimmer sun, high CO2 is necessary to stop the Earth freezing over.
In summary, we know CO2 was probably very high coming into the Late Ordovician period, however the subsequent dip in CO2 was brief enough not to register in the GEOCARB model, yet low enough (with the help of a dimmer sun) to trigger permanent ice-formation. Effectively it was a brief excursion to coldness during an otherwise warm era, due to a coincidence of conditions.
The following (somewhat simplified) diagram may make this easier to understand:
When looking at events such as these from the deep geological past, it is vital to keep in mind that there are many uncertainties, and generally speaking, the further back we look, the more there are. As our paleo techniques improve and other discoveries emerge this story will no doubt be refined. Also, although CO2 is a key factor in controlling the climate, it would be a mistake to think it's the only factor; ignore the other elements and you'll most likely get the story wrong.
Last updated on 24 December 2010 by steve.oconnor.
I'm wondering a little about why the "skeptic argument" above claims that there was glaciation in the "Jurassic-Cretaceous period". It would indeed be bad for the connection to CO2 if there was widespread glaciation during this period, but I can't find anything about that.
In contrast, we're doubling CO2 on a timescale of a century or so. We're also pumping out CH4, N2O, halocarbons, and other greenhouse gases. Thus, if you look at the actual magnitude of the radiative forcings, over the course of the 21st century the increase in greenhouse gases has a much larger forcing than any changes in TSI, Milankovich, etc.
The general idea is that astronomers think that they have good models for the evolution of stars like the sun, so in particular, they can compute solar output from the age of the sun.
There are a couple of very straight-forward holes in these denialist arguments.
1. Ordovician CO2 over 4000 ppm and glaciation proves CO2 doesn't matter! Nope: Look at the distribution of continental landmasses of the Ordovician (~450 MY). Those "glaciers" were the south-polar ice cap. There wasn't much in the way of land in the northern hemisphere.
2. Warming and cooling is purely cyclical! CO2 variation is natural! Sure, there are natural cycles. But something very important and very obvious changed over the geologic time scales involved that makes such simple comparison irrelevant: Plants. Lots of plants. Gymnosperms (conifers etc) originated in the late Devonian-early Carboniferous (380-300 Mya) and angiosperms (flowering plants) in the Cretaceous (100 Mya). All that carbon in the Carboniferous coalbeds? Dead plants that took CO2 out of the atmosphere. The downward trend apparent in the graph above from the Cretaceous forward? More plants. And now we've turned the downward CO2 trend around despite a world rich in plants... maybe we can hope that a whole new class of plant life comes to our rescue... but that would require evolution and the science is still uncertain on that too.
As a rough calculation, an increase in solar irradiance by 4% over the past 400 million years would yield something like +9 w/m2 forcing. Compare that to the anthropogenic CO2 forcing of something like +1.5 w/m2 ...
"if CO2 were to go over 2000 ppm today most of that ice would (eventually) be gone."
Agreed. And I certainly am not questioning the role of solar irradiance.
But the geological proof that ice once existed at our South Pole -- striated bedrock among other unmistakable features -- would still be there. So any future scientific inquiry -- if there is such an enlightened future -- would say "see, they had 'glaciers' in a time of high CO2!" and conclude that CO2 is unimportant.
"increase in solar irradiance by 4% over the past 400 million years" ... "Compare that to the anthropogenic CO2 forcing" 400MY is time enough for evolutionary changes on the grand scale. Isn't anthropogenic forcing is on a time scale of 100s of years? Not enough time for many organisms to get ready for a warmer environment.
Or, another way of putting it is that a much smaller increase in CO2 today will produce a climate that would have required much higher CO2 to achieve in the Paleozoic.
"a much smaller increase in CO2 today will produce a climate that would have required much higher CO2 to achieve in the Paleozoic."
That's an excellent way of putting it.
The Ordovician's big dropoff in CO2 is usually explained by the massive, continent-wide carbonate banks (Trenton, Knox, Arbuckle, Delaware Basin, etc in the US) deposited in warm, restricted shallow seas.
"These carbonate rocks constitute part of the “Great American Bank” (Ginsburg, 1982) that extended more than 3,000 km (1,864 mi) along nearly the entire length of what was the southern seaboard of the Laurentian continental mass" -- Pennsyvania Geological Survey
The deposition of carbonates (Ca0+CO2->CaCO3, calcite) is linked to climatic change in this paper:
"The accumulation of great volumes of carbonates during pre-Hirnantian late Ordovician, in regions where these deposits were previously absent, is suggested as a major sink of atmospheric CO2. This would have caused an important lowering of the average temperature". We don't see such massive carbonates deposited today.
muoncounter:
Thanks for the link to that Villas et al. 2002 paper. That's really neat. They claim that marine carbonate deposition sequestered a mass of carbon equivalent to 350 times the current quantity of atmospheric CO2! I like their explanation of the mechanisms for both the onset and termination of glaciation.
Those mechanisms are critical to the argument over "high CO2 and glaciation=No". It is certainly clear that widespread carbonate deposition takes up lots of atmospheric CO2, but whether that alone causes an ice age isn't clearly established. It is also clear that the graph of CO2 levels taken from a denialist website, posted above (#6), doesn't take a short-term drop in CO2 due to perfectly valid geological mechanism into account.
I have some difficulty with the mechanisms in the "Mountains that froze the world" article John references at the top of this thread. For one thing, the Appalachians weren't all done in the late Ordovician -- it took another 100 MY or so until the Alleghenian Orogeny was complete. The image below is the mid-Ordovician southern ocean:
-- source
All that light blue is shallow sea -- mostly between 10N and 30S latitude -- perfect environment for carbonate deposition from marine organisms.
For another, the idea that Sr86 in Nevada is runoff from the proto-Appalachians just doesn't seem right -- on the map above, Nevada is on the 'north coast' of Laurentia, while the emerging Appalachians are on the 'south coast'.
Other mechanisms abound in the literature, from a mega-volcano to a gamma-ray burst.
From another key paper on this subject, "the waxing and waning of ice sheets during the Late Ordovician were very sensitive to changes in atmospheric pCO2 and orbital forcing at the obliquity time scale (30–40 k.y.)" I've even seen one author who suggests that the concentration of continental land masses at the south pole would perturb the earth's orbit -- but that's a much longer-time scale event.
Please note that I accidentally italicized the last sentence ("We don't see...") in #10. That was my statement and not part of the referenced article.
Also, re: Please note that I accidentally italicized the last sentence ("We don't see...") in #10. That was my statement and not part of the referenced article.
Yes ... and I solved that by inserting a "/i" tag (in brackets) at the beginning of my comment.
:-)
http://wattsupwiththat.com/2010/08/10/study-climate-460-mya-was-like-today-but-thought-to-have-co2-levels-20-times-as-high/
It refers to a new study in PNAS
http://www.pnas.org/content/early/2010/08/02/1003220107.abstract?sid=08063fb7-c9e9-48d7-a515-b3db8907505c
Hope you can comment on this soon.
Doesn't that make it a little pointless what the CO2 levels were 500 mya?
"When CO2 levels were higher in the past, solar levels were also lower"
Can anyone point to a source for the this? And a nice graph showing solar levels in the past?
faint young sun paradox
Solar models are not complete, our understandings of the inner workings of stars is far from ideal and certainly not complete. There are problems with the SSM (Standard Solar Model) and this may or may not impact our model of the evolution of Stars in general, but especially those with similar properties to our sun. Many papers have been written on this subject in recent years. I would direct anyone interested to this article, Problems for the standard solar model arising from the new solar mixture. by J.A.Guzik 2008
http://articles.adsabs.harvard.edu/full/2008MmSAI..79..481G
Whilst I think it is important and helpful to look at climate data in the past, 400My is taking it to extremes as anything we say about that time is largely guesswork based on assumptions and statistical modelling. Anything more than about 5 million years old, in which we have lots of inter-related indicators of climate in the real world is largely pointless, and I would aim that at both sides of this debate. Wasting time on what may or may not have happened 400My ago is not helpful to anyone IMHO.
I've seen this graphic come up a few times to refute this argument and similar ones.
Here's the original source: http://www.geocraft.com/WVFossils/Carboniferous_climate.html
The page's author, Monte Hieb, is listed at the bottom. Poking around a little more on Google will give you a sense of his paleoclimate qualifications.
Please take some time to get acquainted with SkS. See the newcomers guide, browse the 'Skeptic arguments.' There's a lot to learn; it will take some reading, but if you want to understand what's happening, it's well worthwhile.
As far as the geocraft graph, see prior discussion starting with comment #6 on this thread, in which this graph gets debunked.
Easterbrook GISP2
"If CO2 is indeed the cause of global warming, then global temperatures should mirror the rise in CO2"
No, that would only be true if CO2 were the only thing that affects global temperatures. Nobody would claim that is the case.
"In 1945, CO2 emission began to rise sharply and by 1980 atmospheric CO2. had risen to just under 340 ppm. During this time, however, global temperatures fell about 0.9°F (0.5° C) in the Northern Hemisphere and about 0.4°F (0.2° C) globally."
Sulphate aerosols (which have a cooling effect) also rose in the 1940s, but began to be phased out from the early 70s. Dr Easterbrook is just demonstrating his ignorance of the work that has been done on attribution of climate change in the 20th century. It isn't hard to find, there is a whole chapter on it in the IPCC WG1 scientific basis report. Being skeptical is fine, but you do need to know what it is you are skeptical about.
These two errors ought to be enough to make anyone skeptical of Dr Easterbrooks article, I suspect there are others.
Easterbrook treats a local temperature record as if it were a global temperature record, which is obviously a fallacious method. What is more, he treats the last data point in the ice core record as though it were very recent, whereas it is in fact 1855. Comparison with modern Greenland temperatures show that for most of the ice core record, temperatures have been below modern temperatures (and may have been below for all of it). Further discussion on this point should be taken here where they are already discussed in detail.
here and particularly here.
Of course, dont take a warmist blog word for it. Pull the data, check the references (especially the metadata) and see for yourself.
The drop in TSI of 4% is about 54 W/m^2, three doublings of CO2 would be about 12 W/m^2, so that presumably means that for a global glaciation to happen now, the sun would have to dim by about 42W/m^2 or about 3%. To put that into context, the variation of the 11 year solar cycle is about 2W/m^2 and the difference between glacial and interglacial conditions is apparently about 7W/m^2.
Eccentricity is good for a couple watts as well.
DeltaF = 5.35*ln(C/C0)
which implies that
C = exp(DeltaF/5.35 + log(C0))
so substituting the figures, we get
C = exp(7/5.35 + 5.6384) = 1000ppmv (ish)
That calculation ignores any feedback etc, so if it was within a factor of two of the real answer from a climatologist (who unlike me knows what they are talking about ;o), I would be pleasantly surprised. A value of 500ppmv sounds plausible to me.
The last glacial period of any consequence was the so called KT about 230 mya at the Permian-Triassic boundary. This one coincided with the greatest extinctions in the history of life.
The notable one before that was at the end of the Ordovician about 450 mya. There were extinctions but only a few liverworts and mosses and possibly insects had made it on to land. The really wierd thing is that there are glacial tillites with a carbonate cap in Australia, and if we can believe the apparent polar wander paths Australia was pretty close to the equator then.
There was another glacial period about 650 million years ago in the Proterozoic. Everynoe starts getting really grumpy and calling each other names and the apparent polar wander paths diverge before this.
You can see that glacial periods are rare in earth history, ocurring roughly every 200 my. Between hese periods Gloval Average Temperature and CO2 are thought to be higher than now.
Where dies the 5.35 come from in DeltaF = 5.35*ln(C/C0)?
As for terminology... we are currently in an interglacial (i.e. relatively warm) period of the ongoing ice age (i.e. geological period where large ice caps are present).
What you have probably heard people saying is that raising CO2 to ~500 ppm might prevent the next glacial period entirely.
That is, normally we would expect the current interglacial period to end some time in the next 15,000 years or so and then be followed by a long period of increasing cold which would cause glaciers to spread out from the poles for ~90,000 years and then retreat as the next warming cycle comes around. However, if CO2 were raised to 500 ppm then it would likely take more than 100,000 years to return to pre-industrial levels (barring some new technology to sequester it faster than would happen naturally) and could thus keep the planet warm enough that we skip the next glacial cycle entirely.
That'd actually be a good thing... but given that it is thousands of years away not quite as pressing as dealing with the warming we will see over the next two centuries.
This diagram could not prove anything.
1. It is a moving average - and of how many values, nobody knows.
2. The values themselves used in the Moving Average are also averaged values.
3. It is not even accurately calculated. Does anyone have any vague idea why the temperature saturation in the Jurassic and Cretaceous in the upper version of the Diagram is 22°C and in the lower version is 23° C, and how does this average temperature look like as distinct values.
3. This trend in the end of the diagram (in the last 10 million years, for example) is a masterpiece of misrepresentation:
- What part of this period is with Homo sapiens and what without it (how much is 200 000 of 10 mln)?
- What part of this period is with use of fossil fuels and what without?
This 'prediction' is for another system and for another world (without humans and vehicles, and their fresh ideas of how to control the world).
The guys that put back into the air the carbon (in the form of carbon dioxide) should have any idea of what they are doing and how they will clean up the air and the ocean back in case of 'emergency'.
In the past Nature 'regulated' the concentration of CO2 by extinction of species. Who, how, and when will regulate the CO2 produced by the vehicles, for example and which species will extinct first - humans or their cars.
The dinosaurs 'ruled over' the Earth for 160 mln years by virtually doing nothing 'as regulation'.
We, with our fresh ideas of wasting natural resources, mania to control everything, and dealing with things that we don't fully understand will hardly make a million - seriously.
Care to give a reference to back up that assertion? On a timescale of thousands of years CO2 levels are regulated by ocean-atmosphere transfers, over timescales of tens of thousands of years plus by the chemical weathering thermostat. See e.g. David Archers global carbon cycle primer published by Princeton University Press.
Presumably you are referring to the graph posted in comment #6 and at larger scale in #27?
This graph is a cartoon; it is not from an authoritative source and is not taken very seriously.
I am not specialist in the field, and yet according to Craeme Lloyd, Natural History Museum, London, UK more than 99% of all species ever lived on the Earth are extinct at present ... by one reason or another.
RE: The two versions of the Graph
I cannot dispute that both of the versions are absolute cartoons, but they are presented all over the Internet as 'Evidence No.1' that the CO2 and the global temperature 'are falling'.
That should tell you a lot about the quality of those arguments -- and the folks that present them. I'd say the science of using cartoon graphs in place of real data and observation is the real 'climastrology.'
And that is true, except it says nothing at all about CO2 levels.
This volcanic activity, of course, is what likely led to the high atmospheric CO2 levels in the past but my question is this - volcanoes spew alot more then just greenhouse gases. They will also spew dust and other such particles that would have a cooling effect on the earth.
As such, could that also explain the reason for high CO2 levels during a period of glaciation?
I'm not clear on how much volcanic activity has changed over the past 500 million years but what's really fascinating is you can see in the geologic record almost exactly where the Indian continent started bumping up against the Asian continent to start forming the Himalayas and started a long process where CO2 was pulled out of the atmosphere through rock weathering. And along with that you see the global temperature start a long slow decline from the days where you had crocodiles in the Arctic to modern glacial cycles in the Arctic. All of it a function of the amount of CO2 in the atmosphere.
This all fits well with deep glaciation events (Snowball Earth) where the almost complete ice cover of the planet would prevent any rock weathering and thus cause CO2 to build up to very high levels before raising the temperature enough to melt the ice.
Rob Honeycutt - thanks for the article link!