A first-of-its-kind NASA study is finding that cool lakes are heating up — even faster than air.
Two NASA scientists used satellite data to look at 104 large inland lakes around the world and found that on average they have warmed 1.1 degrees (Celsius) since 1985. That's about 2½ times the increase in global temperatures in the same time period.
Russia's Lake Ladoga and America's Lake Tahoe are warming significantly and the most, said study co-author Simon Hook, a scientist at the Jet Propulsion Lab in Pasadena, Calif. Tahoe has heated up by 1.7 degrees since 1985, while Ladoga has been even warmer, going up by 2.2 degrees.
The study was published Wednesday in the journal Geophysical Research Letters.
Hook and his colleague used several satellites and looked at thermal infrared images of the lakes in winter and summer. They also confirmed the numbers by comparing them to buoy data.
"It fits with what we see with air temperature measurements," Hook said. "We were surprised that in some places the lakes appear to be warming more than the air temperature."
Lakes slower to cool than land
The next question to look at is why the lakes seem to be warming faster than the air or land, Hook said. One reason could be the way lakes warm — in a more gradual manner than land but also slower to cool.
NASA climate scientist Gavin Schmidt, who was not part of the study, said the research made sense and adds another independent measuring system to show that the world is warming up. Eleven different indicators — including air temperature, humidity, snow cover, ocean heat content — show statistically significant man-made global warming, while no environmental measurements show otherwise, according to the National Oceanic and Atmospheric Administration.
Warming lakes is indicator No. 12 and "another brick in the wall," said University of Victoria climate scientist Andrew Weaver.
Overall, 41 lakes increased temperatures in a statistically significant way, with another 59 individually warming but not enough to be considered significant. Only four showed temperature drops, but not significantly, Hook said.