Sunday, November 11, 2012

A little lesson about the positive feedback effect

Sent the following to the News and Observer of Raleigh, they printed it on 11/9/12 (link to online version complete with reader comments below):
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In his letter of 11/7, William Everett reports that scientists found a case where temperatures increased before atmospheric carbon dioxide concentrations.  Everett claims this finding invalidates the climate change concept that increasing carbon dioxide concentrations cause temperature increases, since one would expect the carbon dioxide to increase first if it caused a temperature increase.

I believe the report Everett cites refers to climate 20 thousand years ago, and there are times in Earth's history where temperature does increase first, and a carbon dioxide increase follows.  What Everett failed to add is that oftentimes when this happens, the increase in carbon dioxide causes a further and much larger increase in temperature.  And the initial smaller temperature rise was caused by changes in Earth's orbit and orientation (Milankovitch cycles) that simply do not cause today's warming.

A study by Jeremy Shakun, published in the science journal, Nature (volume 484, April 2012), presents convincing evidence that rising carbon dioxide concentrations caused global temperatures to increase from 18 to 11 thousand years ago.  This is but one of many lines of evidence indicating that rising carbon dioxide concentrations in our atmosphere do cause an increase in temperature and consequent climate changes.
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