Ancient global warming: but which came first, the temperature or the CO2?
From the National Oceanography Centre, Southampton (UK)
Variations in atmosphere carbon dioxide around 40 million years ago were tightly coupled to changes in global temperature, according to new findings published in the journal Science. The study was led by scientists at Utrecht University, working with colleagues at the NIOZ Royal Netherlands Institute for Sea Research and the University of Southampton.
“Understanding the relationship between the Earth’s climate and atmospheric carbon dioxide in the geological past can provide insight into the extent of future global warming expected to result from carbon dioxide emission caused by the activities of humans,” said Dr Steven Bohaty of the University of Southampton’s School of Ocean and Earth Science (SOES) based at the National Oceanography Centre in Southampton.
It has been known for some time that the long-term warmth of the Eocene (~56 to 34 million years ago) was associated with relatively high atmospheric carbon dioxide levels. However, scientists were previously unable to demonstrate tight-coupling between variations in atmospheric carbon dioxide and shorter-term changes in global climate.
To fill this gap in knowledge, the authors of the new study focused on one of the hottest episodes of Earth’s climate history – the Middle Eocene Climatic Optimum (MECO), which occurred around 40 million years ago.
Algae use photosynthesis to harvest the energy of the sun, converting carbon dioxide and water into the organic molecules required for growth. Different isotopes of carbon are incorporated into these molecules depending on the environmental conditions under which algae grow. Ancient climate can therefore be reconstructed by analysing the carbon isotope ratios of molecules preserved in fossilised algae.
The researchers took this approach to reconstruct variations in carbon dioxide levels across the MECO warming event, using fossilised algae preserved in sediment cores extracted from the seafloor near Tasmania, Australia, by the Ocean Drilling Program. They refined their estimates of carbon dioxide levels using information on the past marine ecosystem derived from studying changes in the abundance of different groups of fossil plankton.
Their analyses indicate that MECO carbon dioxide levels must have at least doubled over a period of around 400,000 years. In conjunction with these findings, analyses using two independent molecular proxies for sea surface temperature show that the climate warmed by between 4 and 6 degrees Celsius over the same period.
“We found a close correspondence between carbon dioxide levels and sea surface temperature over the whole period, suggesting that increased amounts of carbon dioxide in the atmosphere played a major role in global warming during the MECO,” said Bohaty.
The researchers consider it likely that elevated atmospheric carbon dioxide levels during the MECO resulted in increased global temperatures, rather than vice versa, arguing that the increase in carbon dioxide played the lead role.
“The change in carbon dioxide 40 million years ago was too large to have been the result of temperature change and associated feedbacks,” said co-lead author Peter Bijl of Utrecht University. “Such a large change in carbon dioxide certainly provides a plausible explanation for the changes in Earth’s temperature.”
The researchers point out that the large increase in atmospheric carbon dioxide indicated by their analysis would have required a natural carbon source capable of injecting vast amounts of carbon into the atmosphere.
The rapid increase in atmospheric carbon dioxide levels around 40 million years ago approximately coincides with the rise of the Himalayas and may be related to the disappearance of an ocean between India and Asia as a result of plate tectonics – the large scale movements of the Earth’s rocky shell (lithosphere). But, as explained by Professor Paul Pearson of Cardiff University in a perspective article accompanying the Science paper, the hunt is now on to discover the exact cause.
The researchers are Peter Bijl, Alexander Houben, Appy Sluijs, Henk Brinkhuis, Gert-Jan Reichart (Utrecht University), Jaap Sinninghe Damsté and Stefan Schouten (NIOZ Royal Netherlands Institute of Sea Research) and Steven Bohaty (SOES). The research was funded by the Netherlands Organization for Scientific Research Utrecht University and Statoil, and used samples and data provided by the Ocean Drilling Program (ODP).
Publication: Bijl, P. K., Houben, A. J. P., Schouten, S., Bohaty, S. M., Sluijs, A., Reichart, G-J., Sinninghe Damsté, J. S. & Brinkhuis, H. Transient middle Eocene atmospheric CO2 and temperature variations. Science 330, 819 – 8215 (2010).
DOI: 10.1126/science.1193654
http://www.sciencemag.org/cgi/content/full/330/6005/819
Science Perspective:
Pearson, P. N. Increased atmospheric CO2 during the middle Eocene. Science 330, 763-764 (2010). DOI: 10.1126/science.1197894
http://www.sciencemag.org/cgi/content/short/330/6005/763
h/t Dr. Leif Svalgaard
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Stephen Wilde says:
November 11, 2010 at 12:23 pm
The greenhouse hypothesis doesn’t propose bottom up warming. It proposes additional downward IR warming the surface in the course of delaying the exit of the same energy to space.
However the inability of IR to warm a body of water (as opposed to just a few surface molecules that promptly evaporate) combined with the oceanic control of surface air temperatures means that the extra IR cannot alter the equilibrium temperature of the system as a whole. Instead it just accelerates the hydrological cycle a miniscule unmeasurable amount and the extra energy from that extra downwards IR just vanishes into latent heat and is whisked away by wind and convection for a faster exit to space.
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Stephen, I usually agree w/you, but this assertion is puzzling. I haven’t seen any convincing explanation on why the downwelling IR would be completely converted to latent heat (evaporated water). I agree it will penetrate only a very short distance, but at such small distance scales (a few microns) the absorbed IR would just thermalize & equilibrate via conduction/mixing, which would translate to slightly higher temps of the very top of the water. I understand that evaporative cooling is occurring all the time at the surface (dependent mostly on temp & wind), but I don’t see why the evaporation would increase solely due to absorbed downwelling IR from CO2 any more than from any other IR in the general downwelling wavelengths (none of which penetrate past the “skin” of the water).
I understand evaporation would indeed increase from a surface temp increase, but to say that all (or even most) of the downwelling CO2 IR would be converted to latent heat doesn’t make sense to me. My first guess would be that most of any downwelling IR (from CO2, H2O, etc) would be, because of what I stated above, converted to a temp increase of whatever effective short-term mixing depth occurs near the surface (a couple inches?), and that the evaporation rate would simply follow the usual temp dependence rules.
Hello beng,
Can you or anyone else show that there is any energy left over from the IR from any source not just CO2 to contribute to increased warmth in the body of water below the evaporating layer ?
I’ve been asking for clear evidence of that for some time.
The thing is that evaporation has a net cooling effect so every time a molecule changes state it takes out of the local environment more than the energy required to provoke the change of state. How then can there be anything left over ?
Furthermore every photon of IR gets absorbed by a molecule within the evaporating layer so every one of the affected molecules will change state earlier than it otherwise would have done. How does the IR get any deeper to be absorbed by any molecules that do NOT evaporate.
Note that as a result of evaporation and upward radiation there is a 0.3C cooler layer below the evaporating layer which the energy from the IR cannot cross. That cooler layer is caused by the upward energy loss being faster than the rate at which energy can come up from below.
My assertions are usually just a challenge to someone to clearly rebut them.
Can you do it ?
When my assertions are not clearly rebutted I incorporate them into my comceptual model until such time as they are rebutted.
Why do you scientists make things so hard? . . . when it comes to the past . . .
First thing that came to my mind was when I read this article was the commercial production of dry ice . . . .
Pardon my ignorance, but is it possible that the increased incidence of CO2 was the result of the inferred temperature change?
BINGO!
That’s exactly what was concluded from more recent ice cores, that the atmospheric gas composution follows the temperature record rather than the other way around.
RE: “The rapid increase in atmospheric carbon dioxide levels around 40 million years ago approximately coincides with the rise of the Himalayas and may be related to the disappearance of an ocean between India and Asia as a result of plate tectonics…”
The geology I’ve read suggests some sort of “hot spot” was able to melt away the “roots” of the Indian sub-continent, so that when it broke away from Antarctica it was able to zoom north at a speed something between twice and three times as fast as any continent “drifts” today.
Innocent Asia was just sitting there, minding its own business, with a vast continental shelf which had been accumulating coal and oil and gas for hundreds of millions of years, when along comes this upstart chip of Antarctica and smashes into it. It seems to me very little of the coal and oil and gas in Asia’s continental shelf survived the collision. (Unless there are reserves high up in the Himalayas.)
In other words, Mother Nature burned oil in a manner far more effective than mankind can, and leeched every bit of coal out, even from areas which would be completely inaccessible to man, and squeezed all the natural gas from the pre-collision continental shelf of Asia. One way or another, (and likely involving volcanoes and even limestone being turned to CO2,) a vast amount of “sequestered” CO2 was ejected back into the atmosphere.
If the uptick in CO2 caused warming, and if the warming didn’t “run away” then, why should warming “run away” now?
All that seemed to happen was the world became a warmer and lusher place, a place in many ways more kind to life, and to evolution. Mammals were able to thrive and develop all sorts of new species. The vast release of CO2 gave life a kick in the pants.
Were it not for the release of “sequestered” carbon, a planet might become increasingly cold and sterile, with plants gasping for breath due to so little CO2 being left in the air, and an “Iceball Earth” becoming a distinct possibility.
So…..perhaps those who like to think of Gia as having a mind that thinks, ought think in this manner:
Gia was very worried Earth might turn into an iceball, and all life would freeze. She had to figure out some way to release a lot of sequestered carbon, but there were no continents due to collide, and no asteroids available. Therefore, in a stroke of genius, She evolved humans out squeaky little tree shrews, and, at the last possible moment and in the nick of time, burned up lots of coal, and an ice age was averted.
At the very least, thinking in this manner would allow Moon-bats to feel much more warm and fuzzy about toasting their toes by a warm fire, and might even allow them to be thankful during a Thanksgiving dinner.