My monthly OTOMH column has been published in the CABPRO News, and it is now posted on the CABPRO Report webs site.
It was a drought that is responsible for my interest in long term climate trends. In the 1970s my oldest daughter took an interest in the Anasazi cliff dwellings when we lived in Holbrook, Arizona for a year. The Strategic Air Command Radar Bomb Scoring Unit in Holbrook was my assignment upon my graduation from Air Command and Staff College in 1973. Not an auspicious assignment out of Command and Staff College, but I digress. Our year in Holbrook allowed us to take many family trips to the cliff dwellings scattered throughout Arizona and New Mexico, and eventually Colorado. But, Colorado is another story.
As we visited the cliff dwellings, one of the questions that kept coming up in our discussion was, why did this sophisticated community abandon their fields and dwellings and then vanish? The Internet was not yet a universal research tool, so we visited the local library and started researching possible causes: warfare, weather, famine, etc. We discovered there had been a long period of drought in the mid-11th and 12th centuries which may have contributed to the Anasazi cultural collapse.
Research by paleoclimatologists has confirmed that temperatures rose in the western U.S. from about A.D. 800-1300, known as the Medieval Warm Period, which translated into a series of droughts. The most devastating of these occurred in the mid-11th and 12th centuries, when dry conditions persisted for several decades. As I recall from our research, the longest we found was 27 years.
Paleoclimate data from tree rings and other sources also suggest that the mechanism driving drought during this Medieval Warm Period was eastern Pacific Ocean cooling. Much like a widespread extended La Ni√±a event with cool sea surface temperatures strengthening a persistent moisture-blocking system of high-pressure off the West coast, nudging storm tracks north. This year the blocking is lower down the coast, creating droughts in New Mexico and Texas. We are fortunate that the La Niña this year resulted in a record-breaking snowfall. However, this has not always been the case.
During the Dalton Minimum there was a 13-year drought in coastal California according to Church Mission records. This was also a period when a deep La Niña weather pattern dominated the Pacific. The La Niña weather patterns have been associated with drought throughout climate history We are entering a period of low sun spot activity similar to the Dalton Minimum. The Pacific has entered a cool phase, which promotes more La Niña weather patterns. We could be on the cusp of some long-term periods of drought if history is an indicator.
You can read the rest of my column here, which column concludes:
It is time to start building more of those damn dams. The cold Pacific droughts are just around the corner, and it takes ten years to build a dam as large as the Auburn Dam. Waiting for the droughts to happen before taking action is not an option!