Forests, after all, cool the atmosphere by drinking in carbon dioxide from the air. A new study, however, published in Proceedings of the National Academy of Sciences reports that forests' other climatic effects can cancel out their carbon cleaning advantage in some parts of the world. Using a three-dimensional climate model, the research team mimicked full global deforestation and also studied the effects of clear-cutting in different regions of latitude, such as the tropics and boreal zones. Apparently, these natural carbon sinks only do their job effectively in tropical regions; in other areas, they have either no impact or actually contribute to warming the planet. In fact, according to this model, by the year 2100, if all the forests were cut and left to rot, the annual global mean temperature would decrease by more than 0.5 degree Fahrenheit.

In the 1810, a remarkable transition happened in Denmark: Forests ceased shrinking and began to expand. The turnaround was driven by several factors, such as migration of people to cities and the abandonment of less fertile fields. Forest area subsequently began to recover in the rest of Europe and the United States. Now, an analysis of global forest data suggests that forests are returning in more and more countries, which leads the authors to predict that the volume of wood in the world's forests will likely stabilize in the coming decades.

The data come from the United Nations Food and Agriculture Organization, which last year released a report on the trends in forests from 229 countries between 1990 and 2005. An international group of researchers led by forest ecologist Pekka Kauppi of the University of Helsinki, Finland, dug into the numbers. In a novel approach, the researchers compared trends in both forest area and forest density for the 50 most-forested nations.