Warming lakes speed up methane emissions
A fishing trip on Lake Tanganyika ends: The reduced productivity caused by warming may cut the amount of food available to fish. Image: Worldtraveller via Wikimedia Commons
LONDON, 21 December, 2015 – US scientists report that lakes worldwide are warming by an average of more than 1°C every 30 years, faster than the warming rate of either the ocean or the atmosphere.
The warming is expected to increase algal blooms and to mean global emissions of methane, a greenhouse gas 25 times more potent than carbon dioxide over a century, will increase by 4% over the next decade. Over a 20-year period, methane is 84 times more powerful than CO2.
The rapid warming of the lakes threatens freshwater supplies and ecosystems, the scientists report in their study, published in the journal Geophysical Research Letters. They say their study is the largest of its kind and the first to combine satellite temperature data and long-term ground measurements.
They monitored 235 lakes, representing more than half the world’s freshwater supply, for at least 25 years and found that they are warming by an average of 0.34°C each decade. Among the profound effects they say may follow is an increase in algal blooms.
“These results suggest that large changes in our lakes are not only unavoidable, but are probably already happening”
The blooms, which can ultimately rob water of oxygen, are projected to increase by 20% in lakes over the next century as warming rates increase. Blooms which are toxic to fish and animals would increase by 5%. If these rates continue, the authors say, emissions of methane from the lakes will increase by 4% by 2025.
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