Global warming caused by afforestation in the Southern Hemisphere

Using an earth system model of intermediate complexity (EMIC), the McGill Paleoclimate Model-2 (MPM-2), this paper examines the climatic biogeophysical effects of afforestation in the southern hemisphere (SH) with a focus on land–atmosphere interactions and the modeling influence of the dynamic ocean in the background of the earth system. Increased forest cover affects the albedo feedback and the supply of water, which in turn influences temperature. These changes largely control the net impact of the SH afforestation based on latitudinal band. In response to afforestation in 0–15°S and 0–40°S, the local surface air temperature significantly increases at a maximum value around 5°S during autumn. This warming is attributed to decreased land surface albedo dominating over enhanced precipitation which is resulted from increased tree cover. Forest expansions in 15–30°S and 30–40°S induce diminished land surface albedo and precipitation locally, leading to a warming around 25°S during spring and a warming around 35°S in winter, respectively. The maximum differences in the modeled responses of afforestation on latitude band basis are seen to be 7–10 times larger for the same season. Our results show that capturing how and where biogeophysical changes due to forest expansion warm a specific region requires an accurate global simulation of afforestation geographically. This provides potential for further improving detection and attribution of regional afforestation effects. Furthermore, a dynamic ocean simulation results in a warming compared with a fixed one over most forcing originating areas in response to afforestation. We demonstrate that unless the dynamic ocean is considered we risk influenced conclusions regarding the drivers of temperature changes over regions of afforestation.

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