Greenhouse Gas Effect Consistent Over 420 Million Years

[phantom power]

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.

(...)

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.

(...)

"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, <1.5°C or 5.5°C> the carbon-cycle would have been in a 'perfect storm' condition."

http://www.sciencedaily.com/releases/2007/03/070328155540.htm

[TrogL]

1. Pity they didn't address manmade global warming

or whether it's a correlation or causation.

[GliderGuider]

2. This study was measuring something else entirely

This work addresses a more fundamental issue in atmospheric physics. It's important to know if the sensitivity of the climate to changing CO2 concentrations has remained stable over long periods of time. If it has, then we are probably on the right track in looking at CO2 as a significant forcing factor. Once that is established, then we can build that sensitivity into climate models and have more confidence that their behaviour will approximate reality.