Clayton Sandell holds up a frozen t-shirt during the cold snap of December 2013. ABC News

It was cold. It was brutal. Many T-shirts were frozen in the name of TV news. But a new analysis from the National Center for Atmospheric Research shows that lately, those Arctic cold snaps like the one earlier this month just aren't lasting as long. The graphics below show how things are changing for cities like New York, Atlanta and Chicago (43 consecutive days below freezing in 1977, versus just 11 days this season.) Climate scientists say it's part of a years-long trend in which extreme heat records are outpacing extreme cold records 2-to-1, as humans continue burning fossil fuels that are warming the planet.