Climate change over the past 4000 years
Yesterday, the climate website WhatsUpWithThat published a very readable article by Andy May with a temperature reconstruction over the past 4000 years. I have asked the editors of WUWT to be allowed to translate it for Climate Crazy, of which act:
Andy May, WUWT December 3, 2024
Climate change in the past 4000 years
I last wrote about climate change and civilization in the past 4000 years in 2016. Since then, a lot has changed and I have learned a lot more about the subject. First, we learned that different proxies for air and seawater temperature, such as ice core δ18O or growth rings, are all different. For a discussion of some of the temperature proxies used and the problems with them, see here. Proxies differ in accuracy, are often sensitive to seasons, and have different temporal resolutions. As Soon and Baliunas noted in 2003, they are all local and "cannot be lumped together into a hemispherical or global quantitative composition."
The reconstruction of the global mean surface temperature (GAST) used in the IPCC AR6 report was by Kaufman et al. The authors indicate that the average distance of each temperature (the temporal resolution) is 164 years. To validly compare the entire global instrumental temperature record with the proxies, one must average all daily measurements since 1860 to one point. That is, the rate of warming since 1860 is irrelevant, for the proxy record cannot observe a 164-year increase. The problem of comparing daily modern instrumental temperature readings with proxies is discussed here by Renee Hannon.
https://klimaatgek.nl/wordpress/2024/12/04/klimaatverandering-afgelopen-4000-jaar/
