The Triple Helix @ UChicago

Winter 2016

"Climate Change: Effects on El Niño and Chicago Winter" by Tom Klosterman


Way back in October, the Chicago Tribune predicted a mild winter for Chicago[1], with above average temperatures and below average precipitation. Indeed, the months of December and January were exceedingly mild: the mean temperature was 12ºF above normal in December, and January snowfall was 1.41 inches less than normal.[2] The city has been feeling the effects of this balmy weather: the Chicago Department of Transportation states that it is ahead on its pothead repairs, with only 60% as many to fill as last year.[3] The suburbs La Grange, Westerns Springs, and La Grange Park have all reported using “significantly less” salt than the past two years.[4] These are just two of the factors saving Chicago big bucks this temperate season. 

Whenever temperatures stay above normal for an extended period of time, cries of “Global Warming!” arise from the environmentally concerned, in the same way periods of freezing weather draws cries of “Global Warming?” from the skeptics. Indeed, this winter is showing typical conditions for a planet slowly heating up. Not only are average temperatures rising, there have been fewer extreme weather events like snowstorms and negative temperatures. Across the nation, cities are experiencing record mild temperatures. New York City, for example, is currently experiencing the warmest winter on record.[5] Of course, global warming could be partially to blame for this, but all focus this year has been on a more naturally occurring factor. 

Cue the ENSO weather phase known. The “El Niño Southern Oscillation” has been occurring naturally for thousands of years.[6] It describes atmospheric pressure and ocean temperature changes in the Pacific Ocean, which have far-reaching ramifications around the globe. Every few years, the ENSO typically swings between two states - El Niño and La Niña. seasons with cooler ocean water are named “El Niña” seasons. This causes below average temperatures in many locations, including the Northern Plains and Pacific Northwest of North America. 

But La Niña’s hot-headed brother “El Niño” is winter’s most abominable and feared enemy in the Midwest. El Niño is spurred on by warm waters in the Pacific once every 2 to 7 years on average. To begin, strong westerly winds or other semi-isolated events will cause a small increase of temperature in the Eastern Tropical Pacific. This affects the atmospheric currents, which in turn further heat the ocean, creating a feedback loop.6 Warm, moist air piles up all over the Eastern Pacific throughout the summer. Then, during winter in the United States, the warm air in the Southwest pushes the Polar Jet Stream north, reducing the amount of frigid air brought to the Midwest from the Arctic and raising average temperatures.[7] The previous El Niño season, 2009-2010, was very moderate and eventually was mitigated by non-related atmospheric currents that brought cold air back down from the North. However, El Niño decided to revisit the world in 2015, stronger than ever. The “Super El Niño” we are experiencing now is one of the strongest on record, rivaling the winter of 1997-98, where winter temperatures were 12.4ºF above average. 

And certainly, El Niño seems to be having a huge effect on the Chicago area. Although intermittent periods of heavy snow and cold have developed, overall the winter has been easy and mild. As mentioned above, the city has been saving money and labor due to the warmer temperatures and reduced snowfall. But if you think El Niño could be Mother Nature’s compensation for previous snowy, windy, cold conditions called “snowpocalypes” or “snowmaggedons,” think again. 

El Niño, although convenient for Chicago, causes major global disturbances. The weather pattern causes Southeast Asia to dry up, increasing wildfire risk in areas such as Indonesia. Warm water in the Pacific due to El Niño also encourages “coral bleaching” - the large scale death in coral reefs.[8] As the moist air from the Pacific dumps rain on the Southern US states and northern South America, flooding in the Americas increases. On the other hand, droughts are exacerbated in other places, such as Australia, India, Indonesia, the Philippines, Brazil, parts of Africa, western Pacific islands. And across the globe, non-optimal growing conditions reduce crop production and the profits of fishermen and farmers, especially those from poor countries. Can all of these tragedies be chalked up to the cruel cycles of Nature? 

To answer that, we now return to climate change. 2015, the beginning of our current “Super El Niño,” was the hottest year on record. Even without the overall warming effects of El Niño the year would have kept its record, suggesting reverse causality: did the warmer temperatures caused by greenhouse gases intensify El Niño? 

Several recent studies from Nature Climate Change have proposed that there may indeed be a connection between the increase in global temperatures and the strengthening of recent El Niños.[9,10,11] Future, stronger, El Niños also have the potential to stretch further east, implying even worse effects on the US.[11,12] In light of these investigations and discoveries, perhaps it is unfair to scapegoat Mother Nature completely for Chicago’s mild winter.[13] Having shown to be highly correlated with human greenhouse gas emissions, global warming is a background factor that at the very least does not weaken El Niño. In all likelihood, our carbon dioxide and methane emissions are helping to heat the Pacific Ocean and assisting El Niño in warming the United States, while also ruining crops and inducing both floods and droughts worldwide.


[1] Chicago Tribune Staff. "Latest Projections Still Favor Mild Winter for Chicago." Chicago Tribune, October 15, 2015. 
[2] "Chicago January Weather 2016." AccuWeather. Accessed February 15, 2016. 
[3] Gallardo, M. "City Says It's Ahead on Pothole Repairs Thanks to Mild Winter." ABC7 Chicago. February 1, 2016. 
[4] Mannion, A. "La Grange, Other Towns Use Less Salt Due to Mild Winter." Chicago Tribune, February 11, 2016. 
[5] Erdman, J. "Winter 2015-2016 U.S. Mid-Term Report Card." The Weather Channel. February 6, 2016. 
[6] UK National Weather Service. "El Niño, La Niña and the Southern Oscillation." Met Office. 2012. 
[7] "El Nino Primer." 2015. 
[8] Stone, M. "El Niño Is Killing Earth's Coral Reefs." Gizmodo. February 23, 2016. 
[9] Power, S., et al. "Robust Twenty-first-century Projections of El Niño and Related Precipitation Variability." Nature 502, no. 7472 (2013): 541-45. 
[10] Cai, W., et al. "Increasing Frequency of Extreme El Niño Events Due to Greenhouse Warming." Nature Climate Change 4, no. 2 (2014): 111-16. 
[11] Cai, W., et al. "ENSO and Greenhouse Warming." Nature Climate Change 5, no. 9 (2015): 849-59. 
[12] Santoso, A. et al. Late-twentieth-century emergence of the El Niño propagation asymmetry and future projections. Nature 504, 126–130 (2013). 
[13] Cho, R. "El Nino and Global Warming-what's the Connection?" February 3, 2016.

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