Clouds moderate Amazon deforestation's climate effect.

The Amazon rainforest may be flipping from being a massive carbon sink to a net carbon emitter. Deforestation through intentional fires releases ~1.5 billion tonnes of carbon dioxide (CO2) per year into the atmosphere, which contributes to climate warming (1). Changes in the region's vegetation from land-clearing practices modify atmospheric composition, the fraction of solar radiation reflected from Earth's surface (albedo), and cloud properties. These factors can intensify or stall the warming effect of deforestation, but their contributions are unclear. In particular, clouds regulate Earth's temperature by reflecting incoming sunlight and trapping outgoing heat. On page 429 of this issue, Dror and Feingold (2) report that deforestation of the Amazon rainforest increases cloud cover at low altitudes (<2000 m above sea level), partially offsetting the warming influence of released CO2. The cooling effect is surprising, with possible implications for assessing cloud feedbacks associated with vegetation and greenhouse gas emissions. [ABSTRACT FROM AUTHOR]