CO2 and albedo climate impacts of extratropical carbon and biomass plantations

We explored the climate impacts for two land-use change scenarios, aimed at mitigating the buildup of greenhouse gases in the atmosphere. Using the integrated assessment model IMAGE 2.2, we found that the large-scale implementation in the extratropics of either carbon-sequestration or modern-biomass plantations decreases the CO2 concentration with 70-80 ppmv by the year 2100 compared to a nonmitigation baseline. In a coupled land/atmosphere/ocean/sea-ice model this moderates global warming over the 21st century by 10%. However, the carbon-sequestration option raises the absorption of solar radiation due to a lower albedo compared to the scenario involving modern-biomass plantations (for biofuels production). The albedo-induced difference in global mean temperature is as large as the mitigation by CO2 changes in the two scenarios compared to the baseline. Further, an atmospheric circulation change in the carbon-plantation scenario weakens the supply of moisture from the oceans to North Africa and central Eurasia. In our model this decreases annual mean precipitation over North Africa by up to 10% and further increases summer temperatures over Eurasia. These findings lead us to conclude that other climate impacts than just CO2 changes have to be taken into account when discussing climate-change mitigation options that involve land-use changes.