Are Longer, Hotter Droughts Here to Stay?

In the summer of 2012, 81% of the land area of the contiguous 48 states was in some stage of drought, from Abnormally Dry to Exceptional Drought, according to the US Department of Agriculture. Half the counties in the US — 1,600 counties in 32 states — were declared natural disaster areas by USDA*.

Hot winds, wildfires, and temperatures as high as 110°F (43°C} were recorded in many areas. Crop failures were widespread. Of the crops that survived, yields were expected to be less than half of normal. Lake, river, and reservoir levels were dropping to record lows. 76% of the corn crop was in less than good condition. A smaller US crop yield was expected to result in price increases for a wide range of food products, and contribute to worldwide grain shortages.

Was this extreme and prolonged drought part of a natural cycle, occurring every 40 to 50 years as it had in the past, or did it signal a new trend toward longer, hotter, and more frequent severe drought events?  A research paper published in Proceedings of The National Academy of Sciences presents data showing that these extreme events have occurred far more often in the past 30 years than they did in the prior 30.

The paper, authored by James Hansen of NASA’s Goddard Space Flight Center, compared worldwide surface temperatures recorded from the period 1950-1980, with those from 1980-2010. Using a Bell Curve to compare the data from the two periods, the NASA scientists found that during the 1950-1980 period, 33% of earth’s land area experienced summers defined as “hot”, “very hot”, or “extremely hot”. During the 1980-2010 period, 75% of land area experienced “hot” to “extremely hot” summers, a 225% increase. The data indicated that drought is not only now more widespread, but occurs more frequently than in the past, and with hotter temperatures.

Is global warming the main cause of this rapid shift toward a hotter world? Hansen and his colleagues say that no natural cycle could cause this much change this fast without outside influence.  They believe that global warming, speeded up by the tremendous volume of human-produced greenhouse gasses pumped into the atmosphere, is largely responsible for this quick transition to a hotter earth. Can we slow this process by reducing greenhouse gas production, or are we already past the tipping point? No one knows for sure.

*USDA Drought Intensity Scale based on historical records of drought length and severity: D0-Abnormally Dry (occurred every 3 to 5 years on average), D1–Moderate Drought (5 to 10 years), D2–Severe Drought (10 to 20 years), D3 – Extreme Drought (20 to 50 years), and D4-Exceptional Drought (50 years).