Warm

Warm

An unparalleled heat wave in eastern Europe, coupled with intense droughts and fires around Moscow, put Earth’s temperatures in the headlines this summer. Likewise, a string of exceptionally warm days in July in the eastern United States strained power grids, forced nursing home evacuations, and slowed transit systems. Both high-profile events reinvigorated questions about humanity’s role in climate change. But, from a global perspective, how warm was the summer exactly? How did the summer’s temperatures compare with previous years? And was global warming the “cause” of the unusual heat waves? Scientists at NASA’s Goddard Institute for Space Studies (GISS) in New York City, led by GISS’s director, James Hansen, have analyzed summer temperatures and released an update on the GISS website that addresses all of these questions.

Globally, June through August, according to the GISS analysis, was the fourth-warmest summer period in GISS’s 131-year-temperature record. The same months during 2009, in contrast, were the second warmest on record. The slightly cooler 2010 summer temperatures were primarily the result of a moderate La Niña (cooler than normal temperatures in the equatorial Pacific Ocean) replacing a moderate El Niño (warmer than normal temperatures in the equatorial Pacific Ocean).

As part of their analysis, Hansen and colleagues released a series of graphs that help explain why perceptions of global temperatures vary — often erroneously — from season to season and year to year. For example, unusually warm summer temperatures in the United States and eastern Europe created the impression of global warming run amuck in those regions this summer, while last winter’s unusually cool temperatures created the opposite impression. A more global view, as shown below for 2009 and 2010, makes clear that extrapolating global trends based on the experience of one or two regions can be misleading.

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