Half of the last eight summers in cold regions including parts of Greenland and Russia have been the warmest since 1400, according to a Harvard University study on climate change across high northern latitudes.
The findings, published in the journal Nature, showed that the summers 2005, 2007, 2010 and 2011 were hotter than any point in the previous 600 years. Average temperatures over the last 20 years in those regions rose by about 1.16 degrees Celsius (2 degrees Fahrenheit), said Martin P. Tingley, a Harvard research associate and the study’s lead author.
Tingley and coauthor Peter Huybers used a statistical technique called hierarchical Bayesian analysis to crunch data that included tree-ring density, lake sediments and ice cores from Greenland and the Canadian Arctic. The approach produced a more precise result than previous long-range temperature reconstructions. The more rigorous method reduces controversy and means “more people will start paying attention” to climate change, he said.
“We’ve been pushing for these methods for a number of years now,” said Tingley. “Instead of saying, ‘Recent years are warmer than my best bet at each year in the past,’ we actually came up with a metric that allows for conclusions that take into account that simultaneous-comparison problem.”
The study analyzed data from northern reaches of 45 to 85 degrees latitude. The summer in Russia three years ago was that area’s warmest, the study found.
“Recent observations like the 2010 Russian heat wave can be explained by a shift in the mean” temperature, Tingley said. “These recent years really are warmer.”