Document Type



Global warming, El Nino, weather variability, drought frequency


The global warming since 1980 has been greater than it was during the warming trend from 1880 to 1940. This has caused concern that the very warm years of 1987 and 1988 might have been associated with greenhouse warming. However, the cooling trend from 1940 to 1980 occurred during a rapid buildup in greenhouse gases in the atmosphere. Although there may have been some greenhouse warming since 1880, the unusual warmth of 1987 and 1988 may have been caused by changes in the temperature of the equatorial Pacific Ocean, and changes in transparency of the atmosphere or ocher phenomena acting on the atmosphere.

There have been changes in weather variability associated with the global warming and cooling. The unusually benign period of weather in the Midwest from 1956 to 1973 occurred at the end of a brief period of global cooling. Since 1973, there has been increased weather variability like chat experienced in the 1930's.

The most important factor in weather variability in the Midwest has been associated with the El Nino cycle. Crop production appears to be favored in years of El Nino events. All the major droughts in the Midwest since 1891 have occurred between El Nino years. The El Nino event scares about every 3 to 7 years and lases 1 to 2 years. In the Midwest the year after an El Nino event tends to be warmer and drier than normal and is sometimes a drought year.

Publication Date

September 1990

Journal Title

Journal of the Iowa Academy of Science





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© Copyright 1990 by the Iowa Academy of Science, Inc.



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