Rapidly Warming Lakes Threaten Fresh Drinking Water

December 24, 2015 | Joanne Kennell

Lake Eerie toxic algae bloom
Photo credit: Jesse Allen and Robert Simmon/NASA (cropped)

And food supplies are in trouble too.

A lot of research has been dedicated to studying the effects of climate change on the oceans, including ocean acidification, ocean warming and sea-level rise, but what about freshwater lakes?  What impact is climate change having on them?

A new study, published in the journal of Geophysical Research Letters and conducted by more than 60 scientists, announced on Friday (December 18) that climate change is rapidly heating up lakes around the world, threatening both freshwater supplies and ecosystems across the globe.  

According to the scientists, lakes are warming at an average of 0.61 degrees Fahrenheit every ten years, which is larger than the rate of warming of the oceans and the atmosphere — and this is worrisome.  At this rate of warming, algae blooms, which remove oxygen from water, will increase by 20 percent over 100 years, with 5 percent of the blooms being toxic to fish, animals, and humans — thus making the water undrinkable.

The life living within lakes is very sensitive to temperature changes, especially large temperature swings, and this can lead to the disappearance of organisms and slower growth rates of organic matter.  “Lakes are important because society depends on surface water for the vast majority of human uses -- not just for drinking water, but manufacturing, energy production, irrigation and crops,” said co-author Stephanie Hampton of Washington State University.  “Protein from freshwater fish is especially important in the developing world.”

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The study used a combination of long-term lake measurements and satellite data of more than 235 lakes between 1985 and 2009.  Although 235 lakes are just a fraction of the world’s total, these lakes contain more than half of the world’s freshwater supply.  The lakes had different sizes, depths, and location, but despite this variability, “over 90 per cent of them had a clear signal of warming,” said Sapna Sharma, co-author of the study from Toronto's York University. “I didn't expect to see that.”  It may come as no surprise that lakes in northern and southern climates are warming differently; however, some lakes in both regions are warming faster than average.

In northern climates, some lakes are warming at 1.3 degrees Fahrenheit per decade and losing ice cover earlier each spring since many regions are experiencing less cloud cover. This exposes the lakes to more of the sun’s radiation.  

In southern climates, certain lakes are warming at 0.95 degrees Fahrenheit per decade, and scientists believe some of these southern lakes may have already reached the highest temperatures fish can tolerate.  This is particularly worrisome for the African Great Lakes, which contain one quarter of the world’s freshwater supply and are a large source of fish — which are already showing declines in some populations.

Lake Superior, located in North America, had one of the fastest warming rates in the world, which was quite surprising to researchers since it is a very cold and deep lake.  They concluded that this warming was a result of winter ice melting earlier each spring, exposing the lake to warmer air temperatures for longer and longer each year.

We need freshwater to survive, so we need to protect it.  The only way to reduce the warming of lakes is to reduce our greenhouse gas emissions, and with the Paris climate talks recently ending, it is clear that is definitely something the world is trying to do.

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