Anthropogenic increase of winter surface albedo

Abstract

The range of surface albedo in winter increased fourfold after densely forested swamps in Orange County, New York were turned into farmland, making the local microclimate considerably more sensitive to the presence and duration of snow cover. Today, the peaty onion fields when dry have an albedo of 0.08 when snowfree and 0.79 when covered with fresh snow. Before clearance in the late 18th century, the albedo of the swamps ranged from approximately 0.10 when snowfree to 0.28 when snow covered. Prior to the arrival of white settlers, the regional surface albedo, as modeled over a large portion of southeastern New York, ranged from 0.12 when snowfree to 0.31 when snow covered. It ranged from 0.15 (snowfree) to 0.59 (snow covered) when deforestation peaked in the late 19th century. Present values are 0.14 and 0.47, respectively. As a result of these changes in albedo, we estimate that approximately the same amount of solar radiation was absorbed in the naturally vegetated New York region in a snowy winter (with the ground snow covered 75% of the time) as in a snow-dry winter in the late 19th century (with a 10% duration of snow). Deforestation elsewhere in the middle latitudes has had qualitatively similar effects.