勞倫斯利福摩國家實驗室（Lawrence Livermore National Laboratory）、蒙特帕里爾大學（Université Montpellier II）及卡耐基研究所（Carnegie Institution）的科學家共同提出結論，指出森林植被有吸收陽光減少反射的作用，導致地表加熱而抵銷了吸收碳原子讓溫室氣體減少的功效。研究結果顯示，到西元2100年時，中高緯度地區的森林，會造成某些地區氣溫升高，比起沒有森林的情狀更高華氏十度。
Planting forests in temperate regions such as the United States and Europe may not yield any benefit for the global climate, and may instead contribute to warming, according to a new study set for presentation Saturday at the American Geophysical Society annual meeting in San Francisco.
The process by which less sunlight is reflected and more is absorbed by forest canopies, heating the surface, cancels out the positive effects from the trees taking in carbon, conclude scientists from Lawrence Livermore National Laboratory, Université Montpellier II, and the Carnegie Institution.
Their research shows that, by the year 2100, forests in mid-latitudes and high latitudes will make some places up to 10 degrees Fahrenheit warmer than they would have been if the forests did not exist.
The scientists say theirs is the first study to investigate the combined climate and carbon cycle effects of large-scale deforestation in a fully interactive three dimensional climate carbon model.
Forests affect climate in three different ways, the scientists explain. They help to keep the planet cool in two of those ways. They absorb the greenhouse gas carbon dioxide from the atmosphere and that helps to keep the planet cool, and they evaporate water to the atmosphere and increase cloudiness, which also helps keep the planet cool. "Our study shows that tropical forests are very beneficial to the climate because they take up carbon and increase cloudiness, which in turn helps cool the planet," said co-author Govindasamy Bala, an atmospheric scientist.
But forests also are dark and absorb sunlight, warming the Earth.
"The darkening of the surface by new forest canopies in the high latitude boreal regions allows absorption of more sunlight that helps to warm the surface," said Bala. "In fact, planting more trees in high latitudes could be counterproductive from a climate perspective."
The models calculated the carbon-climate interactions and took into account the physical climate effect and the partitioning of the carbon dioxide release from deforestation among land, atmosphere and ocean. The story is different for the tropical forests. In tropical regions, forests help keep the Earth cool by not only absorbing carbon dioxide, but by evaporating plenty of water as well.