Assessing the relationship between extensive use of organochlorine pesticides and cooling trend during the mid-20th century in the southeastern United States.

In contrast to global warming, temperatures in the southeastern United States have exhibited a decreasing trend of up to 1-2 degrees C over the last century. We investigated the relationship between this cooling trend and the extensive use of organochlorine pesticides--particularly dichloro-diphenyl-trichloroethane (DDT) and toxaphene--in the southeastern U.S. from the mid-1940s through the 1970s. Based on annual use and soil residue estimates, it is shown that enthalpies associated with the endothermic evaporation of pesticides from soil resulted in surface temperature decreases of up to -0.2 degrees C. This is the first study to show the inverse correlation between surface air temperature and pesticide use. These findings highlight the potential contribution of the extensive use of organochlorine pesticides to changes in the surface air temperature, especially in regions of intensive agriculture and pesticide use.