There are six times more heat waves in the Great Lakes than 20 years ago

A study found that there are six times as many heat waves in the Great Lakes today as there were 20 years ago.

Severe heat waves – when water temperatures rise significantly above normal – strike the world’s largest lakes six times more frequently than they did two decades ago.

According to new research, nearly all of the severe heat waves in lakes that have occurred in the last 20 years have been caused in part by climate change, and they could become three to 25 times more likely by the end of the century.

The researchers examined more than two decades of surface temperature data from the world’s largest lakes to determine how frequently lake heat waves occur and how much anthropogenic climate change has contributed to their occurrence.

The researchers discovered that severe lake heat waves are twice as likely to occur on average as they were before the industrial revolution. Heat waves in lakes can alter water conditions, stress aquatic plants and animals, and result in algal blooms and other water quality issues.

The findings were published in Geophysical Research Letters. The study is the first to quantify how anthropogenic (caused by humans) climate change has influenced lake heat waves, providing a critical new perspective on how the world’s lakes are responding to a warming climate.

“What really stood out was the magnitude of the human contribution: most of the severe lake heat waves we observed had a significant anthropogenic footprint,” said R. Iestyn Woolway, a climate scientist at Bangor University in Wales. “There is no escape for aquatic organisms when exposed to these extreme temperatures,” he said, unlike humans, who can use air conditioning or build emergency shade.

The increase in remote sensing data over the last decade has allowed scientists to move away from single-lake studies and address global-scale changes in similar ecosystems, according to Woolway. The researchers examined European Space Agency lake surface temperature data from 78 lakes large enough to sample temperatures from multiple points between 1995 and 2019.

The researchers discovered that severe heat waves in lakes are twice as likely to occur as they were before the industrial revolution.

Woolway and his colleagues searched for heat waves of varying intensities in lakes, but limited their attribution analysis to “severe” or “extreme” heat waves.

The researchers analyzed surface temperature anomalies, or how much warmer temperatures are compared to normal conditions, to determine heat wave severity. During a severe heat wave, lake surface temperatures soar well above the top 10% of all observed temperatures. In general, if humans feel the heat, lakes do as well, according to Woolway.

The researchers combined historical temperature data with climate models from the Intercomparison of Cross-Sector Impact Modeling Project, a large community effort to simulate lake responses to climate change, to estimate how much human climate change has contributed to observed heat waves in lakes and to predict how frequently lakes will experience heat waves over the next century.

The researchers discovered that 1.5 degrees Celsius of global warming above pre-industrial temperatures, the target set in the Paris Agreement, may make severe and extreme heat waves three times more likely in lakes. Under a 3 degree Celsius global warming scenario, which could occur this century with minimal reductions in greenhouse gas emissions, severe heat waves in lakes will be up to 25 times more likely than in a pre-industrial climate. Anthropogenic contributions were also highest in tropical lakes, according to Woolway, echoing other studies that have found that lower latitudes are the most affected by the effects of climate change.

The study may be a conservative estimate of how frequently severe lake heat waves occur because it only looked at large lakes, which may be more resilient to changes and severe heat waves.

“The results could be much worse when we scale these findings to a global scale,” Woolway said.

Severe heat waves in lakes will be up to 25 times more likely under a 3 degree Celsius global warming scenario.

Heat waves in lakes can harm ecosystems in a variety of ways. Even minor changes in water temperature can be fatal for organisms that live in a strictly defined temperature regime. Warmer water also means more evaporation and less mixing, because lake water stratifies, with warm water on top and cooler water trapped beneath. Both of these effects can result in less oxygen, which can stress lake inhabitants like fish who need to breathe.

Grant believes that as the field of lake heat waves advances, combining improved data sets with studies of heat refugia for lake inhabitants will help to refine predictions of lake ecosystem responses to heat.

“Reduced global warming is the only way to deal with this. Lake heat waves will become increasingly severe if temperatures continue to rise “Woolway explained.

 

Article Author Gerluxe

Image: wikimedia