The warming of inland lakes

Global trends in seasonal nighttime lake surface temperatures, 1985-2009. Image credit: NASA/JPL-Caltech. (Click on image to enlarge.)

Scientists at NASA’s Jet Propulsion Laboratory Philipp Schneider and Simon Hook conducted the first comprehensive global survey of temperature trends in major lakes and concluded that they have warmed in the past 25 years consistent with predictions based on other data of global warming.

Because of the high specific heat capacity of water (i.e., the amount of heat necessary to raise the temperature of the substance) most of the long-term “warming” of the planet takes place in large bodies of water, particularly the ocean. This study used satellite data to measure the surface temperatures of 167 large lakes worldwide.

The map above shows the results of the survey. The data comes from thermal infrared imagery from National Oceanic and Atmospheric Administration and European Space Agency satellites. The measurements were taken at night in the summer (July-August-September in the Northern Hemisphere; January-February-March in the Southern Hemisphere) so as to avoid the problems of ice cover on the lakes and cloud cover in the atmosphere.

According to the NASA feature on the study the findings showed

“an average warming rate of 0.45 degrees Celsius (0.81 degrees Fahrenheit) per decade, with some lakes warming as much as 1 degree Celsius (1.8 degrees Fahrenheit) per decade. The warming trend was global, and the greatest increases were in the mid- to high-latitudes of the Northern Hemisphere.”

The data were consistent with the trends found in temperatures recorded in buoys in the Great Lakes and with independent surface air temperature data from NASA’s Goddard Institute for Space Studies. In certain places, however, such as the Great Lakes and northern Europe, water bodies appear to be warming more quickly than surrounding air temperature.

NASA says this about the geographic variation in warming:

“The largest and most consistent area of warming was northern Europe. The warming trend was slightly weaker in southeastern Europe, around the Black and Caspian seas and Kazakhstan. The trends increased slightly farther east in Siberia, Mongolia and northern China.

“In North America, trends were slightly higher in the southwest United States than in the Great Lakes region. Warming was weaker in the tropics and in the mid-latitudes of the Southern Hemisphere. The results were consistent with the expected changes associated with global warming.”

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