Drought alarmists accept Medieval Warm Period

 Paleoclimatologists have warned that the American West could be in for a long period of severe drought, but in doing so have had to accept the existence of the Medieval Warm Period.

Edward Cook of the Lamont-Doherty Earth Observatory in New York and colleagues wrote in the October 8 issue of Science magazine, The western United States is experiencing a severe multiyear drought that is unprecedented in some hydroclimatic records.  Using gridded drought reconstructions that cover most of the western United States over the past 1,200 years, we show that this drought pales in comparison to an earlier period of elevated aridity and epic drought in AD 900-1300, an interval broadly consistent with the ‘Medieval Warm Period’.  If elevated aridity in the western United States is a natural response to climate warming, then any trend toward warmer temperatures in the future could lead to a serious long-term increase in aridity over western North America.

 The researchers say that the key to the drought lies in the weather pattern called La Nina, which is characterized by the upwelling of cold water from the bottom of the Pacific in eastern tropical waters.  Climate models show this reduces rainfall in the West (Reuters, Oct. 7).

The current drought, however, may not be as severe as currently depicted.  In an article accepted for publication in a forthcoming issue of the journal Pure and Applied Geophysics, Roger Pielke, Sr. and colleagues find that, The consequences of the most recent drought have been exceptional for some uses (e.g. suburban watering; wells, cattle grazing), but the precipitation deficit for most areas in Colorado was not exceptional (although quite dry).  The reason for the heightened consequences (and awareness in the media) is that there is more competition for the available water, due to population growth.  This is a human caused shortage due to the population requirements and competition with agricultural uses, not an unprecedented precipitation shortage.