Yes, Summers in the U.S. Really Are Getting Warmer

By Michael D. Lemonick

One of the surest signs that the planet is getting warmer is the fact that record high temperatures are outpacing record lows. As of early August, for example we were able to report that with the year a little more than half over, 2012 had already surpassed all of 2011 in terms of record highs in the U.S.

It’s unfair to compare just two years, of course, since that could just be a weird anomaly — but if you look on a much grander scale, the disparity of record highs in the U.S. vs. record lows has grown wider every decade since the 1970s.

NASA has come up with an animation, prepared in conjunction with the release of a paper by the Goddard Institute for Space Studies' James Hansen, that makes this point far more vividly than any static bar chart could. It simply plots summer temperatures in the Northern Hemisphere, starting in the 1950s, showing the number of days that were unusually hot (red), unusually cold (blue) or pretty much normal (gray). Back in the ‘50s, the plot is a nearly perfect normal distribution (more commonly known as a bell curve), with just as many days falling on the cold side as the warm side. It’s what you’d expect if temperatures were going up and down randomly.

But as the animation moves forward in time, the bell begins to slide to the right: unusually cold days diminish drastically, while unusually hot days become more and more common. By the time the animation ends, in 2011, there’s a whole lot more red than blue.

So if you think summers are getting hotter, you’re absolutely right. It’s just one more reminder that the globe really is warming, thanks in large part to the heat-trapping greenhouse gases we keep pumping into the atmosphere.