Climate Science

Cooler in the Forest

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Science  07 Dec 2007:
Vol. 318, Issue 5856, pp. 1525
DOI: 10.1126/science.318.5856.1525c

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Human activity affects climate in many, sometimes opposing, ways. For example, emissions leading to increased atmospheric greenhouse gas concentrations cause warming, whereas those that raise the aerosol burden cause cooling. Moreover, our overall impact depends not only on what we send directly into the atmosphere but also on how we modify the land. Many analyses have concentrated solely on how land use change alters Earth's albedo, a measure of sunlight reflectivity at the surface, but changes in vegetation induce corresponding variations in moisture and heat fluxes that can have large impacts as well. In an effort to determine the effects on temperature of ecophysiological changes due to land use change in the southeastern United States, Juang et al. analyzed heat and radiation flux data collected via meteorological towers located in three distinct ecosystems: a grass-covered old field, a planted pine forest, and a hardwood forest. They found that although the effect of albedo differences among the different ecosystems was large, with warming of nearly 1°C for the transition from old field to forest areas, the ecophysiological and aerodynamic effects of the same transitions could produce even greater cooling, of >2°C. Thus, contrary to some assertions, conversion of open fields to wooded fields will not necessarily make the world a hotter place. — HJS

Geophys. Res. Lett. 34, L21408 (2007).

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