1. Hadley Centre for Climate Prediction and Research, The Met Office , Bracknell, Berkshire RG12 2SY, UK

Correspondence to: Richard A. Betts Correspondence should be addressed to the author (e-mail: Email:  rabetts@meto.gov.uk).

Abstract

Carbon uptake by forestation is one method proposed¹ to reduce net carbon dioxide emissions to the atmosphere and so limit the radiative forcing of climate change². But the overall impact of forestation on climate will also depend on other effects associated with the creation of new forests. In particular, the albedo of a forested landscape is generally lower than that of cultivated land, especially when snow is lying^{3, 4, 5, 6, 7, 8, 9}, and decreasing albedo exerts a positive radiative forcing on climate. Here I simulate the radiative forcings associated with changes in surface albedo as a result of forestation in temperate and boreal forest areas, and translate these forcings into equivalent changes in local carbon stock for comparison with estimated carbon sequestration potentials^{10, 11, 12}. I suggest that in many boreal forest areas, the positive forcing induced by decreases in albedo can offset the negative forcing that is expected from carbon sequestration. Some high-latitude forestation activities may therefore increase climate change, rather than mitigating it as intended.