FROST FOLLOWED THE PLOW: IMPACTS OF DEFORESTATION ON THE CLIMATE OF THE UNITED STATES

Abstract

The modern vegetated landscape of the United States little resembles the “natural” landscape prior to colonial settlement. Two 10-yr climate simulations with a global climate model using natural and modern vegetation maps for land surface boundary conditions showed that the conversion of forest to cropland in the eastern and central United States cooled climate. Mean annual surface air temperature decreased by 0.6°–1.0°C in the United States east of 100° W. The decrease in daily maximum temperature exceeded that for daily minimum temperature for a decreased diurnal temperature range of about 0.6°C, averaged over the year. The cooling was greatest in the Midwest in summer and autumn, when daily mean temperature decreased by >0.5° and 2.5°C, respectively; daily maximum temperature decreased by 1°–3°C; and diurnal temperature range decreased by about 1°C. U.S. temperature records show that much of the 1800s was anomalously cold, particularly in summer and autumn in the Midwest. Although this was likely caused by natural climate variability, increased volcanic activity, and decreased solar activity, the clearing of forests for agricultural land undoubtedly contributed to the cold temperatures in the eastern and central Unites States.