1. ^*,  Systems Ecology Research Group and Department of Biology, San Diego State University, San Diego, California 92182, USA ^‡,  Statewide Air Pollution Research Center, University of California, Riverside, California 92521, USA^§,  USDA Forest Service, 3200 Southwest Jefferson Way, Corvallis, Oregon 97331, USA ^† To whom correspondence should be addressed.

Abstract

ARCTIC tundra has been a net sink for carbon dioxide during historic and recent geological times^1–4, and large amounts of carbon are stored in the soils of northern ecosystems. Many regions of the Arctic are warmer now than they have been in the past^5–10, and this warming may cause the soil to change from a carbon dioxide sink to a source by lowering the water table^11–12, thereby accelerating the rate of soil decomposition (CO₂ source)^3,13–15 so that this dominates over photosynthesis (CO2 sink). Here we present data indicating that the tundra on the North Slope of Alaska has indeed become a source of carbon dioxide to the atmosphere. This change coincides with recent warming in the Arctic, whether this is due to increases in greenhouse gas concentrations in the atmosphere or to some other cause. Our results suggest that tundra ecosystems may exert a positive feedback on atmospheric carbon dioxide and greenhouse warming.