In his response to my comment regarding lessons from Antarctic ice cores, a letter writer repeats the false dichotomy that one must choose between the conclusions that carbon dioxide affects temperature and that temperature affects carbon dioxide. The evidence supports the conclusion that both affect each other. Carbon dioxide and temperature measurements from the 800,000 year ice core record are highly correlated, with a value of 0.84. The correlation is only slightly larger (0.88) when carbon dioxide lags temperature by 1000 years. If carbon dioxide did not affect temperature the difference in correlation would be far larger.

Correlation is not causation of course, so much more sophisticated analysis is required to identify causality. Such analysis by van Ness published in the journal Nature Climate Change in 2015 concludes, “This analysis is sufficient to demonstrate that temperature influences greenhouse gases, and is consistent with the idea that greenhouse gases drive temperature on a faster timescale.”

Global climate modeling provides another line of evidence. He et al. (Nature, 2013) concludes that a climate model can successfully simulate the end of the last ice age, but only when the measured changes in greenhouse gases are used. Simulations with only changes in the earth’s orbit produce little climate change.

Email me at steven.ghan@gmail.com for the ice core data and both of these papers to see for yourself.

If I have convinced you that carbon dioxide affects climate, which means fossil fuel use must decrease 50 percent to prevent unprecedented warming and associated impacts on mountain snowpack, sea level, etc., would you prefer heavy-handed government regulations or a revenue-neutral market-based approach that lets the market respond to a steadily increasing price on carbon, and returns equal shares of the revenue to each person so they can afford adjustments to reduce their use of fossil fuel?

Steve Ghan

Citizens’ Climate Lobby

Richland, Wash.

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