Afforestation can influence energy and water exchanges between the land and atmosphere by changing the surface albedo, roughness and evapotranspiration efficiency, consequently influencing local temperature. Such effects vary with latitudes, seasons, altitudes, and global warming levels. Therefore, the local temperature effects of afforestation are highly dependent on the background climate. In addition to the abovementioned factors influencing the background climate, atmospheric aerosols are also important drivers of regional climate change. However, it remains unclear whether reducing aerosol pollution can modify the local temperature effects of afforestation.
To address this scientific issue, Weidong Guo and Xin Huang's team from the School of Atmospheric Sciences, Nanjing University, compared the local temperature effects of afforestation across multiple anthropogenic aerosol emission scenarios based onan earth system model of the Coupled Model Intercomparison Project Phase 6 (CMIP6). The results show that if current anthropogenic aerosol emissions are reduced to preindustrial levels, the local cooling effect of afforestation in the mid- and low-latitudeswould be enhanced (up to 0.4°C); the additional cooling effect can partially offset the warming effect of aerosol reductions (Figure 1). Meanwhile, the local warming effect of afforestation in the high-latitudeswould be attenuated. The change in the local temperature effectsof afforestation caused by aerosol reductions is equivalent to an additional 0-8% CO2 absorbed by afforestation. A surface energy balance-basedattribution analysis shows that aerosol reductions lead to more surface solar radiation, and the increased solar radiation is more partitioned into sensible and latent heat fluxes due to the higher roughness and transpiration efficiency of forests, resulting in surface cooling (Figure 2). The model projects that if strict aerosol emission control measures are adopted, the local cooling effect of afforestation in China would be enhanced by 0.13°C in the middle of this century.
Figure 1 Impacts of anthropogenic aerosol emission reductions on the local temperature effects of afforestation
Figure 2 The mechanism for the atmospheric aerosol change regulating the local temperature effects of afforestation
This study reveals that reducing aerosol pollution not only has environmental and health benefits, but also enhances the local climate mitigation potential of afforestation. This conclusion has important implications for developing countries such as China, which are facing the dual pressures of air pollution control and climate warming mitigation. The paper entitled Local surface cooling from afforestation amplified by lower aerosol pollution” was published in Nature Geoscience on August 24, 2023 (https://www.nature.com/articles/s41561-023-01251-x). Soon after being published, this paper attracted widespread academic and media attention. The news entitled “Cleaning the air boosts forests' cooling powers” in the Research Highlight section of Nature reported this work. The paper entitled “Cooler forests in clean air” in the News & Views section of Nature Geosciencecommented on this work. The work is also reported in the Funding Achievement section of the official website of the National Natural Science Foundation of China.
Assistant Professor Jun Ge from the School of Atmospheric Sciences is the first author and corresponding author of the paper. Thecoauthors of the paper include Professor Weidong Guo, Professor Xin Huang, Associate Professor Bo Qiu, andPhD student Yipeng Caofrom the School of Atmospheric Sciences, and Dr. Beilei Zan from Nanjing University of Information Science and Technology. The work was jointly supported by the Key Project (42130602), General Project (42175136), Youth Project (42005096, 42105023) of National Natural Science Foundation of China, and Jiangsu Collaborative Innovation Center on Climate Change.
Article link：Ge, J., Huang, X., Zan, B. L., Qiu, B., Cao, Y. P. and Guo, W. D. Local surface cooling from afforestation amplified by lower aerosol pollution, Nature Geoscience, 16, 781–788 (2023). https://doi.org/10.1038/s41561-023-01251-x
Relevant news and comments：
1. Jeff Tollefson. Cleaning the air boosts forests’ cooling powers. Nature Research Highlight. https://www.nature.com/articles/d41586-023-02677-4
2. Chen, L. Cooler forests in clean air. Nature Geoscience, 16, 758–759 (2023). https://doi.org/10.1038/s41561-023-01253-9
3. National Natural Science Foundation of China,Funding Achievement section. https://www.nsfc.gov.cn/publish/portal0/tab448/info90209.htm