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The mean temperature for the Northern Hemisphere had a warming trend from 1890 to 1950 and a cooling trend since 1950. The eastern and central United States had colder temperatures in 1961–1970 than in 1931–1960. The temperature changes were associated with an adjustment of hemispheric circulation from more frequent zonal flow between 1900 to 1950 to more frequent meridional flow since 1950. Regional variations in magnitude and direction of the change were largely related to position in relation to the upper air westerly wave pattern. Time series of individual circulation indices tend to resemble the step function model of climatic change. [ABSTRACT FROM AUTHOR]

The article highlights a report discussing the pleistocene climatic changes and the distribution of life in East Africa. It reports that the present evergreen forest boundaries are generally not natural, noting that they have been reduced by human agency as much as they would have been appreciable drop in rainfall. It discusses the changes that have occurred in the West African forest for a period prior to 400,000 thousand years ago. It also examines the impact of the subsequent dry period in the areas including Elgon, Kilimanjaro, and the highland forms in Southern Tanganyika Territory.