Did Global Climate Change Heat Up Winter Bicycling In Chicago?

The weather this winter has has been exceptionally favorable for Chicago area cyclists. The combination of the warmest winter weather in 80 years and the snow drought that lasted through the middle of January has made the majority of days during the first two months of winter suitable for bike riding. The Evanston Bike Club got in rides on 25 of the 31 days during December in 2011, up from just 6 days the previous year.

A question that many have been asking is whether the good weather for bike riding is due to global climate change. The most common answer to that question is that weather is so chaotic and variable that it is not possible to attribute localized weather events to climate. Chicago's warm weather this winter can be explained by the effect of La Nina and the Arctic Oscillation . According to Dr. Jeff Masters

"we are experiencing a La Niña pattern of sea surface temperatures in the Pacific Ocean. This pushes the jet stream and the cold arctic air northward.

On top of that, this year's Arctic Oscillation has been stronger.The Arctic Oscillation is a see-sawing pressure difference between the Arctic and lower latitudes.  When the pressure difference is high, a whirlpool of air forms around the North Pole. Last year, the whirlpool motion was weaker, allowing cold air to escape from the polar regions and head southward to the US.

This year the whirlpool has been more forceful, corralling the cold air and keeping it nearer the pole. That has reinforced the La Niña impact."

Thus, the lack of snow may simply be due to normal variations in the occurrence of La Nina. The warm weather is largely due to the Arctic Oscillation. However, I tend to agree with NASA's James Hansen and suggest that the likelihood of such extreme weather is small enough that it is hard not to assume that global warming is playing a role in producing the freaky weather.

The Arctic Oscillation is not particularly well understood. However, it does not require too great a stretch to consider that its unusual behavior this year could somehow be related to the thinning of the arctic ice sheet. The change in wind flow over the thinner ice could be impacting the Arctic Oscillation with the result that cold air is not making its way to Chicago.

Ultimately, there is no definitive answer to the question of whether global climate change is heating up winter bicycling in Chicago this year. However, if 2012 turns out to be another year in which extreme weather causes record setting flooding, droughts, and wild fires, it will strengthen the case for a viewpoint that global climate change is causing the freaky weather in Chicago and across the world.