The moderating or amplifying biophysical effects of afforestation on CO2-induced cooling depend on the local background climate regimes in China

Abstract

Afforestation can significantly influence regional climates through both the biogeochemical and biophysical processes involved in land surface-atmosphere interactions. However, many studies have ignored the biophysical processes that can, in some cases, offset the biogeochemical impacts. In this paper, the amount of atmospheric carbon dioxide absorbed by forests and the surface energy balance changes due to land cover changes from croplands and grasslands to forests were quantitatively analyzed, and the impacts of afforestation on the regional temperatures were thoroughly investigated over various climate zones of China, especially over the temperate and arid regions. According to our analysis, (1) when considering only the CO2-induced effects, afforestation led to carbon sequestration ranging from 267.7 to 531.5 Mg CO2-eq hm−250 yr−1 and carbon sinks ranging from 2.6 to 15.7 Mg CO2-eq hm−250 yr−1 in all climate regions; therefore, the cooling effects were achieved. (2) When considering only the biophysical effects, the increase in the net radiation was greater than the increase in the latent heat fluxes in the arid and semiarid regions. Therefore, the land surface provides a positive heat fluxes to the atmosphere and warms the Earth. In contrast, afforestation leads to a decrease in the net radiation and a large increase in the latent heat flux in humid subtropical regions. The increase in net radiation was less than the increase in the latent heat fluxes over the Tibetan Plateau and mid-temperate humid regions, resulting in atmospheric cooling effects. (3) When considering both the CO2-induced and biophysical effects simultaneously, the potential cooling effects caused by afforestation were amplified 1.3–1.5 times relative to those resulting from considering only the CO2 for the subtropical regions. However, the potential cooling effects in arid and semiarid regions were moderated to only approximately 50% of those when only the CO2 was considered. Therefore, the biophysical processes of afforestation have amplified the CO2-induced changes in the subtropical regions and moderated them in temperate regions, while the reverse is true in arid regions.