I found a link the other day to a government website with global mean precipitation data from 1900 to 2000. Of course, I can’t find the link now (please comment if you have the link, but first see the note at the end of the post).
Anyway, I put the numbers into an Excel spreadsheet and graphed the data and added a trendline. (If you would like a copy of the xls file, please ask for it in the comment section below.) As the world warms it is getting wetter. As Matt Ridley writes in his book The Rational Optimist:
If you take the IPCC’s [International Panel on Climate Change] assumptions and count the people living in zones that will have more water versus zones that will have less water, it is clear that the net population at risk of water shortage falls by 2100 under all their scenarios. (emphasis added)
Even the EPA cites the IPCC (2007) to say much the same thing:
As global mean temperatures have risen, global mean precipitation also has increased. This is expected because evaporation increases with increasing temperature, and there must be an increase in precipitation to balance the enhanced evaporation (IPCC, 2007). Globally, precipitation over land increased at a rate of 1.9 percent per century since 1901, but the trends vary spatially and temporally. Over the contiguous U.S., total annual precipitation increased at an average rate of 6.1 percent per century since 1901, although there was considerable regional variability. The greatest increases came in the South (10.5 percent per century), the Northeast (9.8 percent), and the East North Central climate region (9.6 percent). A few areas such as Hawaii and parts of the Southwest have seen a decrease.
Crops may flourish with warmer climes and more CO2. There is some indication that in California some trees are increasing their ranges in response to this change. While increasing temperatures do have their downside, they also have positive benefits as well.