Study says trend may have serious consequences for water quality, amount of greenhouse gas emissions from water.
Zafrir Rinat Dec 20, 2015

Lakes, including Lake Kinneret, are quickly warming worldwide, according to new research, a trend that may have serious implications for water quality and the rate of greenhouse gas emissions from the water.

The finding are included in a first-of-its kind global report on temperature changes of water surfaces in lakes in summer, published last week in the journal Geophysical Research Letters.

According to the findings, the warming process is the result of a combination of local conditions and climate change (global warming) that is causing temperatures to rise throughout the world.

The survey examined changes in 235 lakes, including Lake Kinneret, over summers between 1985 and 2009. One of the research partners was Dr. Alon Rimmer of the Kinneret Limnological Laboratory. The findings will be presented this week at the annual conference of the American Geophysical Union.

The main finding is that on average, water temperature of lakes worldwide is going up by 0.34 degrees a decade, with the Kinneret rising 0.28 degrees a decade. This is a faster rate than ocean warming, which is estimated at 0.12 degrees a decade. Some lakes were found to be warming at more than one degree a decade – more than the warming of air temperature during this period.

Global warming not solely to blame

Although the research shows that lakes are warming all over the world, scientists note that global warming is not the only reason for the rise; it also depends on local conditions. For example, Kinneret researchers believe that the main reason for the rise in temperature is not the warming of the air, but warming in the lake itself due to the continuing receding level.

Only 10 percent of the lakes in the study were found to have cooled, a trend that may be due to new afforestation of areas around those lakes, which gave them shade, or to ice melt in the area, which brought cold water into those bodies of water.

Lakes covered with ice warmed fastest, due to a reduction in the thickness of the ice covering as a result of global warming.

In some lakes that were not ice-covered, a correlation was found between the lake temperature and air temperature in the summer.

The scientists who took part in the research note that a warming trend like the one they found will lead over the next century to a rise of 20 percent in the growth of algae and 5 percent in the growth of algae containing toxic materials. Lakes are today one of the main sources of drinking water throughout the world, and the growth of such algae endangers water quality.

Greenhouse gases that accumulate in lakes are also expected to be emitted back into the atmosphere a result of the warming of the lakes. Increased evaporation is another effect of the warming, which could endanger this precious resource in arid zones.

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