Nearly 5,700 lakes in the northern hemisphere could permanently lose ice cover this century, 179 of them in the next decade, given current greenhouse gas emissions, despite a possible polar vortex this year, researchers at York University have found.
These lakes include large bays in some of the deepest of the Great Lakes, such as Lake Superior and Lake Michigan, which could become permanently ice-free by 2055 if nothing is done to curb greenhouse gas emissions, or with moderate changes by 2085.
Many of these lakes, which are predicted to no longer freeze, are located near large human populations and are an important source of drinking water. Loss of ice can affect the amount and quality of the water.
"We need ice on lakes to reduce and minimize evaporation rates in winter," says lead researcher Sapna Sharma, an associate professor at the Faculty of Science. "Without ice cover, evaporation rates would increase and water levels would decrease. We would lose fresh water that we need for drinking and everyday activities. Ice cover is extremely important both ecologically and socio-economically."
The researchers, including postdoctoral fellows Kevin Blagrave and Alessandro Filazzola, examined 51,000 lakes in the northern hemisphere in order to use annual winter temperature projections from 2020 to 2098 with 12 climate change scenarios to predict whether these lakes would become ice-free.
"With increased greenhouse gas emissions, we expect a greater rise in winter air temperatures, which are likely to rise much more than summer temperatures in the northern hemisphere," says Filazzola. "It is this few degrees of warming from carbon emissions that will cause sea ice to be lost in the future."
The most endangered lakes are in the southern and coastal regions of the northern hemisphere, some of which are among the largest lakes in the world.
"It's pretty dramatic for some of these lakes, which are often frozen, but within a few decades they stop freezing indefinitely," says Filazzola. "It's pretty shocking to imagine a lake that doesn't normally freeze anymore."
The researchers found that most lakes are no longer frozen when the air temperature is above -0.9 ° C. In shallow lakes, the air temperature can be zero or slightly higher. Bigger and deeper lakes need colder temperatures to freeze – some as cold as -4.8 ° C? as shallow lakes.
"Ice cover is also important to maintain the quality of our freshwater," says Sharma. "In years when there is no ice cover or when the ice melts earlier, it has been observed that summer water temperatures are warmer, primary production, plant growth and the presence of algal blooms increase, some of which can be toxic."
To preserve the lake's ice cover, more aggressive measures to reduce greenhouse gas emissions are now needed, Sharma says. "I was surprised at how quickly we can see this transition to permanent loss of ice cover in lakes that had previously been frozen almost constantly for centuries."