Buying carbon offsets to assuage your green guilt? Study says don't bother

Study: trees not cure for global warming

BY MARGARET MUNRO, POSTMEDIA NEWS  JUNE 18, 2011

Planting trees may help appease travellers' guilt about pumping carbon into the atmosphere.

But new research suggests it will do little to cool the planet, especially when trees are planted in Canada and other northern countries, says climatologist Alvaro Montenegro, at St. Francis Xavier University in Nova Scotia.

"There is no magic bullet" for global warming, says Montenegro, "and trees are certainly not going to be providing it."

He assessed the impact of replanting forests on crop and marginal lands with Environment Canada researcher Vivek Arora. Their study, published Sunday in Nature Geoscience, concludes "afforestation is not a substitute for reduced greenhouse-gas emissions."

The United Nations, environmental groups and carbon-offset companies are invested heavily in the idea that planting trees will help slow climate change and global warming. International authorities have long described "afforestation" as a key climate-change mitigation strategy.

But the study says the benefits of tree planting are "marginal" when it comes to stopping the planet from overheating.

Trees do suck carbon [dioxide] out of the air, but the study highlights that their dark leaves and needles also decrease the amount of solar radiation that gets reflected by the landscape, which has a warming effect.

Cropland - especially snow-covered cropland - has a cooling effect because it reflects a lot more solar energy than forests, the scientists say. This so-called "albedo effect" is important and needs to be incorporated into assessments of tree planting programs and projects, the researchers say.

Montenegro and Arora stress that planting forests has many benefits - trees provide habitat for wildlife and prevent soil erosion. And planting forests does help reduce atmospheric levels of carbon dioxide because carbon is locked into wood as trees grow.

But planting trees will have only a modest effect on the global temperature, according to their study, which used a sophisticated climate modelling system developed by Environment Canada. [see Top 10 Reasons Why Climate Model Predictions are False]