The writer of the Nov. 7 letter “Skeptical on CO” reports that scientists found a case where temperatures increased before atmospheric carbon dioxide concentrations. He 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 the letter-writer cites refers to climate 20,000 years ago, and there are times in earth’s history where temperature does increase first, and a carbon dioxide increase follows. What the writer failed to add is that often 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 (Vol. 484, April 2012), presents convincing evidence that rising carbon dioxide concentrations caused global temperatures to increase from 18,000 to 11,000 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.