Profound ecosystem changes expected
The world’s lakes are rapidly warming under a blanket of man-made greenhouse gases, threatening freshwater supplies and ecosystems, according to scientists who studied 25 years of satellite data and measurements from 235 lakes on six continents.
The findings show that lakes are warming far faster than either the oceans or the atmosphere — at a rate of 0.61 degrees Fahrenheit per decade. The warming is projected to have profound impacts, including a 20 percent increase in algal blooms that can rob lakes of oxygen and kill fish.
The NASA and National Science Foundation-funded study is clear that the trend presents serious environmental threats to the environment.
“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. The threats extend beyond drinking water to manufacturing, for energy production, for irrigation of our crops, Hampton explained.
“Protein from freshwater fish is especially important in the developing world,” she said.
“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.
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.”