A combination of satellite data and ground measurements, such as
from instrumented buoys like this one in Lake Tahoe on the California/Nevada
border, were used to provide a comprehensive view of changing lake
temperatures worldwide. The buoy measures the water temperature from above
and below.
Credits: Limnotech
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Climate change is rapidly warming lakes around the world,
threatening freshwater supplies and ecosystems, according to a new NASA and
National Science Foundation-funded study of more than half of the world’s
freshwater supply.
This image of Lake Tahoe,
from the ASTER instrument on Terra, shows the lake’s temperature variations
(cold is blue, warm is red).
Credits: NASA
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Using more than 25 years of satellite temperature data and ground
measurements of 235 lakes on six continents, this study -- the largest of its
kind -- found lakes are warming an average of 0.61 degrees Fahrenheit (0.34
degrees Celsius) each decade. The scientists say this is greater than the
warming rate of either the ocean or the atmosphere, and it can have profound
effects.
The research, published in Geophysical Research Letters, was
announced Wednesday at the American Geophysical Union meeting in San Francisco.
As warming rates increase over the next century, algal blooms,
which can rob water of oxygen, are projected to increase 20 percent in lakes.
Algal blooms that are toxic to fish and animals are expected to increase by 5
percent. Emissions of methane, a greenhouse gas 25 times more powerful than
carbon dioxide on 100-year time scales, will increase 4 percent over the next
decade, if these rates continue.
“Society depends on surface water for the vast majority of human
uses,” said co-author Stephanie Hampton, director of Washington State
University’s Center for Environmental Research, Education and Outreach in
Pullman. “Not just for drinking water, but manufacturing, for energy
production, for irrigation of our crops. Protein from freshwater fish is
especially important in the developing world.”
Water temperature influences a host of its other properties critical
to the health and viability of ecosystems. When temperatures swing quickly and
widely from the norm, life forms in a lake can change dramatically and even
disappear.
“These results suggest that large changes in our lakes are not
only unavoidable, but are probably already happening,” said lead author
Catherine O'Reilly, associate professor of geology at Illinois State
University, Normal. Earlier research by O’Reilly has seen declining
productivity in lakes with rising temperatures.
Study co-author Simon Hook, science division manager at NASA’s Jet
Propulsion Laboratory (JPL) in Pasadena, California, said satellite
measurements provide a broad view of lake temperatures over the entire globe.
But they only measure surface temperature, while ground measurements can detect
temperature changes throughout a lake. Also, while satellite measurements go
back 30 years, some lake measurements go back more than a century.
Global changes in lake
temperatures over the past 25 years. Red shades indicate warming; blue shades
indicate cooling. The study found Earth’s lakes are warming about 0.61
degrees Fahrenheit (0.34 degrees Celsius) per decade on average, faster than
overall warming rates for the ocean and atmosphere.
Credits: Illinois
State University/USGS/California University of Pennsylvania
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“Combining the ground and satellite measurements provides the most
comprehensive view of how lake temperatures are changing around the world,” he
said.
The researchers said various climate factors are associated with
the warming trend. In northern climates, lakes are losing their ice cover
earlier in the spring and many areas of the world have less cloud cover,
exposing their waters more to the sun’s warming rays.
Previous work by Hook, using satellite data, indicated many lake
temperatures were warming faster than air temperature and that the greatest
warming was observed at high latitudes, as seen in other climate warming
studies. This new research confirmed those observations, with average warming
rates of 1.3 degrees Fahrenheit (0.72 degrees Celsius) per decade at high
latitudes.
Warm-water tropical lakes may be seeing less dramatic temperature
increases, but increased warming of these lakes still can have significant
negative impacts on fish. That can be particularly important in the African
Great Lakes, where fish are a major source of food.
“We want to be careful that we don’t dismiss some of these lower
rates of change,” said Hampton. “In warmer lakes, those temperature changes can
be really important. They can be just as important as a higher rate of change
in a cooler lake.”
In general, the researchers write, “The pervasive and rapid
warming observed here signals the urgent need to incorporate climate impacts
into vulnerability assessments and adaptation efforts for lakes.”
NASA uses the vantage point of space to increase our understanding
of our home planet, improve lives and safeguard our future. NASA develops new
ways to observe and study Earth's interconnected natural systems with long-term
data records. The agency freely shares this unique knowledge and works with
institutions around the world to gain new insights into how our planet is
changing.
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