The frigid weather gripping much of America is not unprecedented, but it feels that way. The 21st century has been unusually warm, likely due to climate change. Data from 240 weather stations across the U.S. show there have been fewer days of extreme cold blanketing the country since 2001, compared with the previous 25 years. Experts in weather and behavior say that is why Americans feel the cold more intensely now. But they say the longer this cold snap lasts, the easier it will become to tolerate.