Recently, John Holdren, science advisor to President Obama, said that the punishing droughts underway in California and the Colorado River basin are consistent with the mainstream understanding of the long-term effects of climate change.
Not surprisingly he was attacked by Sen. Jeff Sessions (R-AL), who quoted a Colorado political scientist as follows: “Drought has ‘for the most part, become shorter, less frequent, and cover a smaller portion of the U.S. over the last century.’ Globally, ‘there has been little change in drought over the past 60 years.’ ”
The internal quotes are from a report of an American panel on temperature extremes in the U.S. published in 2008 and from a 2012 article in Nature.
Trouble is, the poli-sci guy and the senator omitted the sentence that follows the “little change” remark above. The omitted sentence reads: “The main exception is the Southwest and parts of the interior of the West, where increased temperature has led to rising drought trends.”
It is not smart to debate science with Dr. Holdren from a cherry-picker.
Holdren, in an extensive reply published by the White House, takes Sen. Sessions, and the poli-sci professor, Dr. Roger Pielke, to school in a very thorough way. I produce just one small passage:
- In a warming world, a larger fraction of total precipitation falls in downpours, which means a larger fraction is lost to storm runoff (as opposed to being absorbed in soil).
- In mountain regions that are warming, as most are, a larger fraction of precipitation falls as rain rather than as snow, which means lower stream flows in spring and summer.
- What snowpack there is melts earlier in a warming world, further reducing flows later in the year.
- Where temperatures are higher, losses of water from soil and reservoirs due to evaporation are likewise higher than they would otherwise be.
Sounds like California to me.
Full disclosure: Dr. Holdren is a friend, though we’ve been out of touch since way before he joined the Obama administration. He is one of the smartest people there is, and not to be trifled with.