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"In our best estimate, the conversion of cropland to forests brings about cooling in

all areas of the planet where afforestation is viable, including areas above 50°N."

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Montenegro, A., et al.,

"The net carbon drawdown of small scale afforestation from satellite observations,"

Global and Planetary Change (2009)

doi:10.1016/j.gloplacha.2009.08.005

Conclusions

The climatic effects of small scale afforestation based on the analysis of high resolution satellite data are markedly different from previous climate model-based results. Results show no simple relation between afforestation efficiency and latitude. In our best estimate, the conversion of cropland to forests brings about cooling in all areas of the planet where afforestation is viable, including areas above 50°N. In fact, many of the areas with the highest afforestation induced carbon drawdown are found at high latitudes. Also contrasting with earlier studies is the relatively low afforestation drawdown over some low latitude areas. Changes in cloud cover could be an important component of the radiative response to afforestation, particularly at low latitudes, but at the scales pertinent to individual afforestation projects observations demonstrate that cloud cover frequency is not

controlled by the presence or absence of forests.

While the overall picture is one where afforestation appears to be a more viable mitigation option than previously believed, uncertainty in the data still point to a worst case scenario where afforestation generates very low net carbon drawdown or even net warming at both high and low latitudes.

The efficiency of afforestation is location dependent and has an average of about 50%. By not considering albedo effects, the current carbon accounting system of the Kyoto Protocol grossly overestimates afforestation drawdown. The use of satellite data allows the impact of albedo changes on afforestation to be calculated at a resolution of ~ 5 km. It also circumvents risks associated with the complex modeling of snow cover, vegetation and surface albedo. Our results demonstrate that analyses like the one conducted here can generate reliable, site-specific estimates of this very important but presently ignored process.