World Climate Report

Over the past decade, considerable debate existed regarding the temperature history of the Earth on the time scale of millennia. If you followed our (WCR) discussion on the subject, you know that one camp would like you believe that the highly-publicized warming of the planet over the past century is absolutely unprecedented over the past few thousand years. This group seems to fixate on the “hockey stick” representation of the temperature history of the past 1,000 years, and they hold on to the stick in spite of evidence to the contrary. Many others have argued based on proxy evidence throughout the world that the past few thousand years include a very warm period 1,000 years ago and a cold period 500 years ago; in their eyes, the warming of the past century is not at all unusual. These folks even go on to suggest that the Earth today may not be yet as warm as conditions 1,000 years ago, despite the 100 ppm increase in atmospheric carbon dioxide over the past century.

Several articles have appeared in Energy and Environment recently with results of considerable interest to us at World Climate Report. The first piece is by Dr. Craig Loehle who received his Ph.D. in mathematical ecology in 1982 from Colorado State University. Loehle gathered as many non-tree ring reconstructions as possible for places throughout the world. There are dozens of very interesting ways to peer into the climatic past of a location, and Loehle included borehore temperature measurements, pollen remains, Mg/Ca ratios, oxygen isotope data from deep cores or from stalagmites, diatoms deposited on lake bottoms, reconstructed sea surface temperatures, and so on. Basically, he grabbed everything available, so long as it did not rely on trees (about which Loehle and World Climate Report show “are not simple thermometers”!)

Following publication of the first article, several errors came to light regarding how temperatures were reported from the various locations. In the second paper, Loehle and co-author J. Huston McCulloch decided to re-do all the calculations, including improvements in terms of confidence intervals. The improved plot below shows little change from the graph above, although for data reasons, the last point now represents the 29-year average temperature centered on 1935. The two statistical wizards note “The corrected data continue to show the Medieval Warm Period (MWP) and Little Ice Age (LIA) quite clearly.” The confidence intervals “indicate that the MWP was significantly warmer than the bimillennial average during most of approximately 820-1040 AD, at the 5% level (2-tailed). Likewise, the LIA was significantly cooler than the bimillennial average during most of approximately 1440-1740 AD.”

See full size image here

We suspect you have been living your life unaware of the articles by Loehle and McCulloch. The reason is obvious - they found evidence that temperature variations over the past 2,000 years indicate that the earth’s average temperature bounces around naturally to a larger degree than other paleo-reconstructions indicate, and further, that temperatures about 1,000 years ago were not that dissimilar to today’s temperatures. This suggests that the earth’s ecosystems are more resilient (and adaptive) than some pessimists give them credit for - not a favorite topic in the mainstream press.