NASA Study Finds Earth's Lakes Are Warming

WASHINGTON -- In the first comprehensive global survey of temperature trends in major lakes, NASA researchers determined Earth's largest lakes have warmed during the past 25 years in response to climate change.

Researchers Philipp Schneider and Simon Hook of NASA's Jet Propulsion Laboratory in Pasadena, Calif., used satellite data to measure the surface temperatures of 167 large lakes worldwide.

They reported an average warming rate of 0.81 degrees Fahrenheit per
decade, with some lakes warming as much as 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.

"Our analysis provides a new, independent data source for assessing
the impact of climate change over land around the world," said
Schneider, lead author of the study published this week in the
journal Geophysical Research Letters. "The results have implications
for lake ecosystems, which can be adversely affected by even small
water temperature changes."

Small changes in water temperature can result in algal blooms that can
make a lake toxic to fish or result in the introduction of non-native
species that change the lake's natural ecosystem.

Scientists have long used air temperature measurements taken near
Earth's surface to compute warming trends. More recently, scientists
have supplemented these measurements with thermal infrared satellite
data that can be used to provide a comprehensive, accurate view of
how surface temperatures are changing worldwide.

The NASA researchers used thermal infrared imagery from National
Oceanic and Atmospheric Administration and European Space Agency
satellites. They focused on summer temperatures (July-September in
the Northern Hemisphere and January-March in the Southern Hemisphere)
because of the difficulty in collecting data in seasons when lakes
are ice-covered and/or often hidden by clouds. Only nighttime data
were used in the study.

The bodies studied were selected from a global database of lakes and
wetlands based on size (typically at least 193 square miles or
larger) or other unique characteristics of scientific merit. The
selected lakes also had to have large surface areas located away from
shorelines, so land influences did not interfere with the
measurements. Satellite lake data were collected from the point
farthest from any shoreline.

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.

The satellite temperature trends largely agreed with trends measured
by nine buoys in the Great Lakes, Earth's largest group of freshwater
lakes in terms of total surface area and volume.

The lake temperature trends were also in agreement with independent
surface air temperature data from NASA's Goddard Institute for Space
Studies in New York. In certain regions, such as the Great Lakes and
northern Europe, water bodies appear to be warming more quickly than
surrounding air temperature.

For more information about NASA and agency programs, visit:


Source: NASA

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