Perhaps the most basic quantity is average Arctic temperature, and Tingley said that the summers of 2005, 2007, 2010 and 2011 were each warmer than all years prior to 2005 in at least 95% of the ensemble members. Furthermore, the rate of temperature increase observed over the last century is, with 99% probability, greater in magnitude than centennial trends during any other interval in the last 600 years. At a more regional level, the summer of 2010 featured the warmest year in western Russia with 99% probability and also featured the warmest year in western Greenland and the Canadian Arctic with 90% probability.
Also notable, Tingley said, was that although summer temperatures are clearly on the rise, they found no indication that the variability of temperature has changed. Events like the 2010 Russian heat wave and the 2003 Western European heat wave are consistent with the increase in mean temperature, after accounting for the fact that they are selected as some of the hottest years and locations.
"Insomuch as the past is prologue for the future", Tingley said, "these results suggest that the hottest summers will track along with increases in mean temperature." He explained that, "if instead the distribution of temperatures were becoming wider, as well as shifting towards higher values, then the probability of extreme events would go up even more rapidly."
But Tingley also pointed out the limitations of the results and the need for further work. "The proxies, unlike thermometers, generally only give information about seasonal average temperatures, and we have not explored changes in variability at the daily and weekly timescales associated with weather patterns. It will be interesting to further explore instrumental records and higher resolution proxies for trends at these shorter timescales."
|Contact: Peter Reuell|