The severity of this year's heat wave and drought, compared with those of 1934 and 1936, is disputed. Does 2012 support the idea of a warming planet?
Underlying the heat wave, as in the 1930s, was the persistent ridge of high pressure running northward from Mexico to Canada. Blocking patterns form in response to cooler-than-normal ocean water off the coast of California. Fewer and weaker storms move inland from the Pacific across the continental United States, leaving a dry interior.
The droughts of 1988, 1956 and especially the 1930s "Dust Bowl" dwarf 2012. Based on the Palmer Drought Index, more than 60 percent of the nation has been abnormally dry or experiencing extreme drought. At its maximum, the 1930s mega-drought encompassed more than 85 percent of the country.
With July over, the National Climatic Data Center and wire services announced a new record monthly high. But the satellite temperature record does not show this July to be warmer than those in earlier years of the past decade. Contradiction begs explanation.
In August Senate testimony, John Christy, director of the Earth System Science Center of the University of Alabama at Huntsville, stated the Data Center calculates records using a data set known as T-mean. It averages the maximum with the minimum temperatures at a particular weather station on a given date. It all sounds reasonable until the climatology is examined.
T-max is the maximum temperature in mid-afternoon when the lower atmosphere is well mixed and offers a "representative sample." T-min is observed at or just before dawn. In rural settings, the early observation is a good indication of true temperature, but only near the ground.
When residential and commercial development encroaches, the station no longer produces representative data because airflow patterns cause warmer air aloft to mix in with air cooled by overnight radiation at ground level. Thus, T-min and T-mean are progressively contaminated with positive bias.
July's "record high" temperature reflects the over-arching influence of urbanization. If July 1936 had been affected by comparable urbanization, the new U.S. record of July 2012 would have fallen short.
Warmists dismiss recent cold winters as "just weather." Then is this heat wave climate change? While the United States sweltered, our Olympic athletes competed in a chilly and wet England.
Only the eastern two-thirds of the United States was much above normal throughout the summer. The U.S. heat wave was not global in extent or evidence for global warming.
William D. Balgord, Ph.D., a consultant and writer, heads Environment &Resource Technology in Middleton, Wis.