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Climate Change Rapidly Warming World’s Lakes

Foto: Philipp Schneider, NILU (Bildet er kuttet og tilbasset heroformatet)

KJELLER/SAN FRANCISCO, December 16th  — Climate change is rapidly warming lakes around the world, threatening freshwater supplies, ecosystems and fish, according to a new study spanning six continents.

More than 60 scientists from dozens of research institutes worldwide including NILU – Norwegian Institute for Air Research took part in the research, published in the journal Geophysical Research Letters and announced last night (Norwegian time) at the fall meeting of the American Geophysical Union.

The study found that lakes are warming an average of 0.34 degrees Celsius each decade. That is greater than the warming rate of either the oceans or the atmosphere, and according to the scientists, it can have profound effects.

Fastest warming in Northern Europe

At the current rate, algal blooms, which can ultimately rob water of oxygen, are projected to increase 20 percent in lakes over the next century. Algal blooms that are toxic to fish and animals would increase by five percent. And these rates imply that emissions of methane, a greenhouse gas 25 times more powerful than carbon dioxide, will increase four percent over the next decade.

– The research is groundbreaking in the sense that for the first time it brings together global satellite data on lake surface temperature with the world’s largest collection of ground-based measurements of lake temperature compiled so far, says Philipp Schneider, senior scientist at NILU and lead of the satellite data analysis for the study. – The two datasets complement each other and allow us to better detect patterns of change of global lake temperatures in both time and space and to improve our understanding of the underlying mechanisms.

While no lakes in Norway were included as part of the study, the research indicates that the most rapidly warming lakes worldwide are located in Northern Europe (primarily Sweden, Finland, the Baltic States, and Northwestern Russia). It is therefore likely that Norwegian lakes exhibit a similar behaviour and are warming rapidly.

Temperature changes life in lakes

Temperature is one of the most fundamental and critical physical properties of water. It controls a host of other properties that include intricate living processes that have evolved within strict boundaries. When the temperature swings quickly and widely from the norm, life forms in a lake can change dramatically and even disappear.

Funded in part by NASA and the National Science Foundation, the study is the largest of its kind and the first to use a combination of long-term hand measurements and temperature measurements made from satellites, offsetting the shortcomings of each method.

Satellite measurements provide a broad view of lake temperatures over the entire globe. But they only measure surface temperature, while hand measurements can detect changes in temperature throughout a lake. Also, satellite measurements go back only 30 years while some lake measurements can go back more than a century.

A total of 235 lakes were monitored for at least 25 years. While that’s a fraction of the world’s lakes, they contain more than half the world’s freshwater supply.

More dramatic in the North

The researchers said various climate factors are associated with the warming trend. In northern climates, lakes are losing their ice cover earlier, and many areas of the world have less cloud cover, exposing their waters more to the sun’s warming rays.

Many lake temperatures are rising faster than the average air temperatures. Some of the greatest warming is seen at northern latitudes, and in particular in Northern Europe, where rates can average 0.72 degrees Celsius per decade. Warm-water, tropical lakes may be seeing less dramatic temperature increases, but increased warming of these lakes can still have large negative impacts on fish.  That can be particularly important in the African Great Lakes, home to one-fourth of the planet’s freshwater supply and an important source of fish for food.

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.”

Kart som viser trender for innsjøtemperaturer over hele verden fra 1985 til 2009
Map of trends in lake temperatures worldwide from 1985 to 2009. The vast majority of lakes is warming according to the first global study combining satellite and ground-based information.

Read the study

O’Reilly, Sharma, Gray, Hampton et.al. Rapid and highly variable warming of lake surface waters around the globe. Geophysical Research Letters 2015. http://onlinelibrary.wiley.com/doi/10.1002/2015GL066235/full

See the video from the press conference in San Francisco (YouTube)