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 0.6Њ-1.0ЊC in the United States east of 100Њ W. The decrease in daily maximum temperature exceeded that for daily minimum temperature for a decreased diurnal temperature range of about 0.6ЊC, averaged over the year. The cooling was greatest in the Midwest in summer and autumn, when daily mean temperature decreased by Ͼ0.5Њ and 2.5ЊC, respectively; daily maximum temperature decreased by 1Њ-3ЊC; and diurnal temperature range decreased by about 1ЊC. 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.

Impact of agricultural practice on regional climate in a coupled land surface mesoscale model

“…We found a 1.3°C warming in midday air temperature during the first 2 weeks following harvest. In a 10 year climate simulation, Bonan [1999] found that conversion from forest to crop resulted in a decline in midday temperature of 0.6°-1°C and 1°-3°C in the east and midwest, respectively. In a similar study, Bounoua et al [2002] reported a 0.7°-1.1°C decline in temperate regions due to land cover conversion.…”

“…Over the past ten years, coupled atmosphere and land surface models have been developed, allowing a quantitative exploration of these interactions. The effect of land cover change on the climate of the United States has been studied by comparing current, historical, and in some cases, future land cover scenarios [Bonan, 1997[Bonan, , 1999Bounoua et al, 2002;Copeland et al, 1996;DeFries et al, 2002;Pan et al, 1999]. These studies reported regional and seasonal differences in response to land cover change.…”

“…DeFries et al [2002] projected that future land cover conversion will be concentrated in the tropics and subtropics, and conversion will warm these regions. Studies centered on the United States have found that historical land cover change, particularly the conversion of forest to cropland, has produced a cooling in the central and eastern United States and a warming in the western United States [Bonan, 1997[Bonan, , 1999Pan et al, 1999]. Bonan [1997Bonan [ , 1999 showed that modeled response was greatest during the summer months and diminished in fall when crops have been harvested and trees have lost their leaves.…”

“…Studies centered on the United States have found that historical land cover change, particularly the conversion of forest to cropland, has produced a cooling in the central and eastern United States and a warming in the western United States [Bonan, 1997[Bonan, , 1999Pan et al, 1999]. Bonan [1997Bonan [ , 1999 showed that modeled response was greatest during the summer months and diminished in fall when crops have been harvested and trees have lost their leaves. Pan et al [1999] further demonstrated that the land surfaceclimate system response was not sensitive to climate regime (i.e., normal, flood, or drought conditions) for any climate parameters considered (i.e., latent and sensible heat fluxes and surface air temperature) except precipitation.…”

Macrophysiology for a changing world

“…For example, in tropical regions, forest removal has substantial impacts on moisture regimes of remnant patches, so altering the value of what might appear to be suitable habitat patches and thus changing species demographics and distributions ( Webb et al 2006). Likewise, in temperate areas, the removal of forests promotes frost conditions and an increase in the frequency of freeze-thaw cycles (Bonan 1999). The latter have substantial impacts on organisms by either reducing growth rates or negatively affecting organismal energy balance during unexpectedly warm conditions, leading to mortality (Irwin & Lee 2003).…”