Lake Superior 3 degrees higher than historic average in October

In late October, the National Oceanic and Atmospheric Administration (NOAA) posted Lake Superior water temperatures that were nearly three degrees Celsius warmer than the historic average.

The historic average temperature for Lake Superior on Oct. 20 is 8.8 C. But this year on that date, the water had a surface temperature of 11.6 C, the second highest temperature ever recorded on that day. The warmest Oct. 20 temperature ever was recorded in 2021.

Some unusually mild fall weather this year made October feel more like August in northwestern Ontario, smashing several daytime temperature records in the region by as much as nine degrees Celsius.

Although the impact of the fall heat may not be immediately obvious, it seems to be helping Lake Superior stay relatively warm for this time of year. That continues a trend in recent years that impacts underwater ecosystems, and coastal weather.

It’s seasonal temperature fluctuations like this that researchers like Jay Austin have been observing for years. Austin has a PhD in physical oceanography and is a professor with the University of Minnesota Duluth. He said warm air temperatures have a large impact on the greatest lake.

“It’s not rocket science.” says Austin.”It is sort of expected that if you have warm air temperatures, the lake is going to cool off less quickly.– Jay Austin, physical oceanographer

“It’s not rocket science,” Austin said. “It is sort of expected that if you have warm air temperatures, the lake is going to cool off less quickly. But what’s really surprising is how little just about anything else matters. And so if you know the air temperature, you can pretty reliably predict water temperature.”

Austin said water temperatures have been gathered across the Great Lakes by instrument and satellite readings for decades. He said looking at the last 40 years, water temperatures on Lake Superior have been inching upward. Austin said above-average water temperatures can have an effect on the ecosystems, including creating a welcoming environment for algae blooms.

“One implication is that we have a longer period where we have warm water at the surface, which tends to be the time when it’s most biologically productive,” said Austin.

Lake Superior is one of the fastest-warming lakes in the world according to Great Lakes Integrated Sciences and Assessment (GLISA). The research group said this can be partially attributed to earlier spring ice melt which allows for longer periods of lake stratification and more exposure to solar radiation. On its website, GLISA notes summer lake surface temperatures on Lake Superior have increased by an average of 2.5°C between 1979 and 2006.

Margueritte Xenopoulos is a professor at Trent University and Canada Research Chair in Global Change of Freshwater Ecosystems.

Xenopoulos and a group of her researcher peers are calling for more winter science on the Great Lakes to try to get a feel for what the future holds.

“For example, warmer weather is expected to increase the nutrient runoff into the Great Lakes,” she said. “We have to be able to predict and forecast if our drinking water is becoming unsafe. We’re talking about 40 million people that live, play and rely on the Great Lakes on both sides of the border. And so without this monitoring, we’re not able to provide the best type of information to to these people.”

Xenopoulos said more knowledge about the changes happening will help people adapt to climate change around lakes like Superior and how best to mitigate some of the potential negative impacts.