Posted on 03/29/2007 9:30:26 AM PDT by cogitator
New calculations show that sensitivity of Earth's climate to changes in the greenhouse gas carbon dioxide (CO2) has been consistent for the last 420 million years, according to an article in Nature by geologists at Yale and Wesleyan Universities.
A popular predictor of future climate sensitivity is the change in global temperature produced by each doubling of CO2 in the atmosphere. This study confirms that in the Earth's past 420 million years, each doubling of atmospheric CO2 translates to an average global temperature increase of about 3 Celsius, or 5 Fahrenheit.
According to the authors, since there has continuously been life on the planet over this time span, there must be an ongoing balance between CO2 entering and leaving the atmosphere from the rocks and waters at Earth's surface. Their simulations examined a wide span of possible relationships between atmospheric CO2 and temperature and the likelihood they could have occurred based on proxy data from geological samples.
Most estimates of climate sensitivity have been based on computer simulations of climate or records of climate change over the past few decades to thousands of years, when carbon dioxide concentrations and global temperatures were similar to or lower than today. Such estimates could underestimate the magnitude of large climate-change events.
To keep Earth's carbon cycle in balance, atmospheric CO2 has varied over geologic time. Carbon-cycle models balance chemical reactions that involve carbon, such as photosynthesis and the formation of limestone, on a global scale. To better predict future trends in global warming, these researchers compared estimates from long-term modeling of Earth's carbon cycle with the recent proxy measurements of CO2.
This study used 500 data points in the geological records as "proxy data" and evaluated them in the context of the CO2 cycling models of co-author Robert Berner, professor emeritus of geology and geophysics at Yale who pioneered models of the balance of CO2 in the Earth and Earth's atmosphere.
"Proxy data are indirect measurements of CO2 - they are a measure of the effects of CO2," explained co-author Jeffrey Park, professor of geology and geophysics at Yale who created the computer simulations for the project. "While we cannot actually measure the CO2 that was in the atmosphere millions of years ago, we can measure the geologic record of its presence. For example, measurement of carbon isotopes in ancient ocean-plankton material reflects atmospheric CO2 concentrations."
Led by Dana L. Royer, assistant professor of Earth and Environmental Sciences at Wesleyan University, who did his graduate work in geology at Yale, the collaboration simulated 10,000 variations in the carbon-cycle processes such as the sensitivity of plant growth to extra CO2 in the atmosphere. They evaluated these variations for a range of atmospheric warming conditions, using the agreement with the geologic data to determine the most likely warming scenarios. The model-estimated atmospheric CO2 variations were tested against data from ancient rocks.
Other proxy measurements of soil, rock and fossils provided estimates of CO2 over the past 420 million years. Calculation of the climate sensitivity in this way did not require independent estimates of temperature. It incorporated information from times when the Earth was substantially warmer and colder than today, and reflects the sensitivity of the carbon-cycle balance over millions of years.
"Our results are consistent with estimates from shorter-term records, and indicate that climate sensitivity was almost certainly greater than 1.5, but less than 5.5 degrees Celsius over this period," said Park. "At those extremes of CO2 sensitivity, [1.5C or 5.5C] the carbon-cycle would have been in a 'perfect storm' condition."
ping -- heavy science
Correct me if I am wrong, but isn't he simply confirming the thesis that CO2 leads to warmer temperatures?
If that is the case, then the burning of fossils fuels, which clearly lead to the release of large amounts of CO2 would be raising temperatures and therefore support theories of anthropgenic climate change.
Obviusly it has occurred for natural reasons in the past, but there is nothing in the article judgmental one way or the other about the cause of the increase in CO2. Or am I missing something?
I saw nothing about causation or whether CO2 leads or lags temperature
Less than one tenth of one percent, or .001, is not a significant amount of CO2 scientifically, and is all that mankind can be accused of creating.
The order appears to be the other way. Increased temperature produced increased partial pressure CO2. Somebody can produce a chart of data from cores.
I seem to remember reading about a report a year or so ago, and maybe you can help me track it down, about the Himalayan limestones evolving enormous amounts of CO2 due to increased rainfall. It's neither here nor there, just something from flash memory.
I'm still working on that in my profile, point #5. On the million year timescales this covers, any lag is unnoticeable.
Send me a private mail to remind me tomorrow. These are necessarily short replies right now.
Unless, of course, the opposite is true - that an average global increase of 3 degress Celcius triggers a doubling of CO2 in the atmosphere.
An article like this supports climate sensitivity to anthropogenic CO2 increases, which has been estimated by several other methods (with appropriate error bars). The range is 1.5 to 4.5 C in the IPCC. 3C lands right in the middle.
Still working on explaining this in my profile. You have to have a different radiative forcing factor capable of inducing that large a temperature change independent of atmospheric CO2 concentrations. The main secondary factor (speaking from the paleoclimate community perspective) in glacial-interglacial transitions was albedo. On Berner's timescales, erosion rates and plate tectonics are major players.
Gee, maybe the sun did it?
I don't see why not. I doubt anybody rewrote the laws of physics during all that time.
How an Open Market Might Save the Planet
Chilling Intolerance for Free Speech on Global Warming
Global Warming on FreeRepublic
Latest from Global Warming News Site
Healthy Coastal Wetlands Would Adapt To Rising Oceans
Thinning Of West Antarctic Ice Sheet Needs Improved Monitoring To Reduce Uncertainty
Oops! Sorrrrr-reeeeee!
Of course, if AGW ultimately is a net benefit, perhaps I'll be saying "good luck" instead of "sorry luck."
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.