Will Global Warming Stop the Snow?

I bet you’ve heard it before, maybe in the news, from your uncle, or maybe from a skeptical friend. How can climate change be happening if we are getting so much snow? The reasoning seems sensible – as temperatures go up, the amount of snow should go down, kind of like a seesaw. After all, we don’t have snow in summer because it is too warm – precipitation falls as rain. But we are experiencing climate change, temperatures are going up, and in the Great Lakes we are getting more snow. How can that be possible?

Part of the story lies with a very common weather phenomenon in the Great Lakes region: lake effect snow. This phenomenon happens when cold, dry air coming from the Arctic flows over relatively warm water. As this happens, the water at the lake surface warms the cold air right above it, and this warm air, in turn, allows more  water molecules at the surface of the lake to evaporate. With the additional heat, the air near the surface becomes less dense than the air above and begins to rise. As the air rises, it cools, allowing the water vapor it holds to condense and freeze and form big puffy clouds. Eventually the ice in the clouds falls as snow on the lake and on the land on the other side of the lake. This is a simplified diagram of how this phenomenon works:

Credit: Laura Rico-Beck

These are amazing snow storms that dump huge amounts of snow in a really short time. The storm itself is made of tightly focused bands of really heavy snow that produce huge flakes – the result of lots of circulation within the clouds. You may not know what I mean if you’re in Chicago, but if you’ve ever lived in Buffalo, or happened to be in Erie, PA last December, I am sure you know what I’m talking about.

OK, I gotta tell you – Erie got 53 inches of snow in two days! That’s more snow in 30 hours than during any 13-day span since 1890, according to the Weather Channel.

Because of the location of the Great Lakes relative to the path of the cold air coming from the Arctic, lake effect snow tends to fall most often on the east and southeast coasts of the lakes, although it can fall anywhere within a few miles from any lake’s shore, including over Chicago from time to time. These are the snowbelts of the Great Lakes – places where you can pretty much count on getting your workout through shoveling for much of the winter:

Source: noaa.gov

Source: noaa.gov

 So, how does climate change affect the amount of lake effect snow we get in the Great Lakes region? There are two factors at stake: First, as we already talked about, lake effect snow systems are fueled by warm lake waters – the warmer the water, the more fuel available for the storms. Second, lake effect snow can only work if the cold air from the Arctic comes in contact with the warmer surface waters of the lakes — once ice covers about 15% of the lake surface, the lake effect snow system shuts down.

So how do you think those variables have been affected by climate change?

I know that by now you are probably dying to see some data, preferably in graph form. So, here you go:This set of graphs from the US Army Corps of Engineers show that, over the last five decades, water surface temperatures have risen (that’s the black lines nested within each of the bar graphs). The reason for the zig-zaggy nature of the lines, and the difference in warming between lakes is beyond the scope of this blog post, but notice that the trend is the same everywhere: lake surface waters are getting warmer.

The graph below by Great Lakes Environmental Research Lab researcher Jia Wang, shows the amount of ice cover in all the Great Lakes (squiggly line) and a line of best fit (straight line) showing the trend in the data. As you can see, the amount of ice cover on the Great Lakes has steadily decreased since the 1970s.

The net effect of climate change in the Great Lakes region has been that lake surface waters have gotten warmer, increasing evaporation as well as the amount of moisture and energy available for developing lake effect snow systems. At the same time, ice cover on the lakes has decreased markedly (and it has formed later in the winter season), allowing lake effect snow systems to develop more broadly and to develop for longer periods of time . The result is an undeniable increase in the amount of lake effect snow as a result of climate change.

Ice coverage of the Great Lakes between 1973 and 2010. (Wang 2012)

Snowfall over Syracuse, NY between 1915 and 2001. (Burnett 2003)

It seems contradictory – a warming climate is producing more snow – but we have to remember that climate and weather systems are made up of a whole lot of variables that interact in really complex ways, and sometimes when one side of the see-saw goes up, so does the other.