By Joby Warrick
Lakes around the world are growing rapidly warmer, according to a new scientific study that warns of potential consequences ranging from depleted fisheries to harmful algae blooms that kill fish and contaminate water supplies for cities large and small.
Hotter freshwater lakes are yet another sign of global climate change, and their increasing temperatures are happening at a faster rate compared to the warming seen in the oceans and atmosphere, a team of scientists report in the peer-reviewed journal Geographical Research Letters.
The study is based on decades of measurements from 235 lakes that contain more than half the world’s fresh water supply. On average, temperatures are rising by about six-tenths of a degree Fahrenheit per decade, a rapid increase by geological standards.
The results are a “wake-up call,” especially for regions that rely on lakes for food and drinking water, said Henry Gholz, a program director for environmental biology at the National Science Foundation, which co-funded the research along with NASA.
“Our knowledge of how lakes are responding to global change has been lacking,” Gholz said.
The study, the largest of its kind, involved more than 60 scientists who used temperature records as well as satellite data to gauge changes over time, from Lake Tahoe on the California-Nevada border to the tropical lakes of central Africa to partially frozen lakes in Scandinavia.
The most dramatic increases were observed at far-northern lakes, which are warming at an average rate of 1.3 degrees F per decade. But tropical lakes also are warming rapidly, the researchers found. Only a small number of warm-water lakes kept a constant temperature or cooled slightly, a departure from the norm that scientists attributed to local land-use changes such as reforestation that increased shade along the shoreline.