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RTD info logoMagazine on European Research Special issue - May 2005   
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Title  The greenhouse phenomenon and climatic feedback

The composition of the atmosphere imprisoned in polar ice informs researchers about the glacial and interglacial episodes which our planet has experienced, including how greenhouse gases, such as CO2 and CH4, are involved in these processes as part of a feedback loop.

Ice coring at the Vostok research station has shown that over the past 420,000 years, levels of CO2 and CH4 in the atmosphere have constantly been changing. During glaciations, these levels fell in line with the temperature, while during periods of interglacial warming, they rose.

But which phenomenon triggered the other? Was it a rise in temperature which caused an increase in gas levels, or vice versa?

Today, the phenomenon is well understood by scientists. The cyclical climate variations read in ice cores are initiated by astronomic events, such as changes to the distance between the Sun and the Earth, or to the inclination of the Earth's axis. But once they have been triggered, higher concentrations of atmospheric gases have an amplifying “feedback” effect.

For example, methane is produced by the fermentation of bacteria found in periglacial marshland regions (Northern Canada, Siberia, etc.). Imprisoned in the permafrost, these encased bacteria come alive during interglacial periods and start producing large quantities of methane, which amplify the greenhouse effect and raise the temperature even further. Conversely, when a new glacial episode starts, the first periods of cold numb these bacteria, which quickly become blocked, causing a rapid reduction in the atmospheric methane concentration.

The same logic applies to the oceans and CO2, where such changes are the work of phytoplankton.

Just one other thing. Although the mechanism outlined above can seem simple and almost instantaneous on paper, in fact, these amplifying and accelerating effects of climate trends last for… several thousand years.

In the last two centuries, due to the industrial revolution, CO2 levels have gone outside the ‘envelope’ of regular cyclical CO2/temperature variation of the last 400,000 years (ppmv = parts per million by volume).
In the last two centuries, due to the industrial revolution, CO2 levels have gone outside the ‘envelope’ of regular cyclical CO2/temperature variation of the last 400,000 years (ppmv = parts per million by volume).
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