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Afforestation Not Likely To Reverse Global Warming

June 20, 2011

Afforestation, or the replacing of farmlands or unused open areas with forests is being encouraged under the UN’s Kyoto Protocol climate-change treaty under the theory that forests are will soak up carbon dioxide (CO2) from the air through photosynthesis, AFP is reporting.

Environmental researchers, in a new probe, said that even massive conversion of land to forestry would have only a slender benefit at best against the increase of greenhouse gasses in the atmosphere.

The primary reason is that forests take decades to mature and CO2 is a long-lasting molecule, able to lurk for centuries in the atmosphere. Another reason is that forests, even as they absorb greenhouse gas, are darker than croplands and absorb more solar heat, which can result in warmer temperatures in higher latitudes.

Vivek Arora of the University of Victoria in British Columbia and Alvaro Montenegro of St. Francis Xavier University in Nova Scotia modeled five scenarios in which afforestation was carried out over 50 years, from 2011 to 2060.

Using a program called CanESM1, the researchers simulated the impacts on land, sea and air if Earth’s surface temperature rose by some 5.4 degrees Fahrenheit by 2100 compared to 1850.

Even if all of the available cropland was forested, this would reduce the warming by only 0.81 F on a timescale of 2081-2100, according to the study, which appears in the journal Nature Geoscience. Fifty-percent afforestation would break it by an even tinier 0.45 F.

Both scenarios are, of course, unrealistic because of the need to grow food.

Growing new forests on half of the current crop land would require at least a doubling in crop yield to feed the human population because half of the crop area would be taken out of use.

The other three scenarios found that afforestation in the tropics was three times more efficient at “avoided warming” than in northerly latitudes and temperate regions.

The study said that afforestation does have other benefits, for the economy and the ecosystem. “There’s nothing wrong with afforestation, it is positive, but our findings say that it’s not a response to temperature control if we are going to be emitting (greenhouse gases) this way,” Montenegro told AFP.

Stated bluntly in the report: “Afforestation is not a substitute for reduced greenhouse-gas emissions.”

Policymakers would be advised to focus afforestation efforts in the tropics but also push hard against deforestation, which accounts for 10 to 20 percent of greenhouse-gas emissions globally. Avoiding deforestation is under discussion for post-2012 climate action under the UN flag.

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