Hansen, et al., wrote in 1999 that empirical evidence does not lend much support to the notion that climate is headed precipitately toward more extreme heat and drought. The drought of 1999 covered a smaller area than the 1988 drought, when the Mississippi almost dried up. And 1988 was a temporary inconvenience as compared with repeated droughts during the 1930s Dust Bowl that caused an exodus from the prairies, as chronicled in the Steinbeck book, The Grapes of Wrath.
But how can the absence of clear climate change in the United States be reconciled with continued reports of record global temperature? Part of the answer is that U.S. climate has been following a different course than global climate, at least so far. They compare the temperature history in the U.S. and the world for the past 120 years. The U.S. has warmed during the past century, but the warming hardly exceeds year-to-year variability. Indeed, in the U.S. the warmest decade was the 1930s and the warmest year was 1934. Global temperature, in contrast, had passed 1930s values by 1980 and the world has warmed at a remarkable rate over the last 25 years.
This early Hansen report illustrates the scientific method of digging into a complex scientific matter, during which Hansen and others soon learned that CO2 and other greenhouse gases were in the process of driving the temperature up on Earth. Naysayers cite this report as evidence that Hansen changed his mind, but should be expected as new information was developed by Hansen and others. That is a good example of the scientific method.
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