Droughts and Heat Waves

The extreme drought across the southern U.S. Plains has certainly exasperated the intense heat the that has persisted through the summer. Did climate change play any role?

There is just not enough data to say for certain that climate change played a role in the unusual heat and drought across parts of the U.S. this year, but it is likely that it had a hand in it.

Scientists and computer models have consistently shown that as we continue to see an increase in greenhouse gases into the atmosphere the number of extreme heat waves will continue to grow. It has also been shown that severe drought will become more common in certain regions of the world.

Compare the two NASA images below. The first one shows where the worst drought conditions were over the U.S. in July. The brown areas indicate where there is much less green vegetation compared to normal. Green areas indicate where there was more green vegetation compared to normal.

The second image shows were the hottest temperatures compared to normal were located during the peak of the July heat wave. As you can see, the driest areas compared to normal are pretty much where the highest temperature anomalies are.

With little or no moisture in the ground, the drought acts as a positive feedback to the heat since the sun's energy can go almost 100% directly to heating the ground instead of initially having to evaporate water from the ground (normal situation), which has a cooling effect.

Also keep in mind, with less vegetation there is also a reduction in evaporation.

----------- Speaking of July......

According to NOAA, July 2011 was the 7th warmest July on record for land/sea combined going back to 1880.

Here is an updated graph of all the July temperature anomalies going back to 1880 from NOAA.