Polar Vortex: The Big Freeze

Steam rises from downtown buildings as temperature begin to climb above zero for the first time in more than 30 hours. (AFP)

The cold weather has closed schools, wreaked havoc on public transportation and forced more than 1,500 flights to be cancelled at O'Hare Airport. (AFP)

Tourists avoid sub-zero temperatures outside by taking in the city views from inside the John Hancock building. (AFP)

A sedan sits encased in ice after firefighters battled a nearby fire in bitter cold below-zero temperatures. (AFP)

Organic farmer Will Muir of Wholesome Living Farm breaks through the ice on a pond so his cows can access drinking water in the midst of bitter cold below-zero temperatures. (AFP)

A horse wears a winter covering while grazing at pasture in the midst of bitter cold below-zero temperatures. (AFP)

Lasharn Harvey protects herself and her dog Sahara, 5, from the cold underneath a large sleeping bag at the McPhearson Square Metro station beneath the Department of Veterans Affairs. (AFP)

People brave the frigid temperatures while walking in Downtown Crossing. (AFP)

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