Institute for Atmospheric and Climate Science, Eidgenössiche Technische Hochschule (ETH) Zurich, 8092 Zürich, Switzerland;
Laboratoire des Sciences du Climat et de l'Environnement (LSCE), Unité Mixte de Recherche (UMR) 1572 Commissariat à L'Energie Atomique-Centre National de la Recherche Scientifique-Université de Versailles Saint-Quentin-en-Yvelines, 91191 Gif sur Yvette, France; and.
Proc Natl Acad Sci U S A. 2014 Jul 8;111(27):9757-61. doi: 10.1073/pnas.1317323111. Epub 2014 Jun 23.
Changes in agricultural practices are considered a possible option to mitigate climate change. In particular, reducing or suppressing tillage (no-till) may have the potential to sequester carbon in soils, which could help slow global warming. On the other hand, such practices also have a direct effect on regional climate by altering the physical properties of the land surface. These biogeophysical effects, however, are still poorly known. Here we show that no-till management increases the surface albedo of croplands in summer and that the resulting cooling effect is amplified during hot extremes, thus attenuating peak temperatures reached during heat waves. Using a regional climate model accounting for the observed effects of no-till farming on surface albedo, as well as possible reductions in soil evaporation, we investigate the potential consequences of a full conversion to no-till agriculture in Europe. We find that the summer cooling from cropland albedo increase is strongly amplified during hot summer days, when surface albedo has more impact on the Earth's radiative balance due to clear-sky conditions. The reduced evaporation associated with the crop residue cover tends to counteract the albedo-induced cooling, but during hot days the albedo effect is the dominating factor. For heatwave summer days the local cooling effect gained from no-till practice is of the order of 2 °C. The identified asymmetric impact of surface albedo change on summer temperature opens new avenues for climate-engineering measures targeting high-impact events rather than mean climate properties.
农业实践的改变被认为是缓解气候变化的一种可行选择。特别是减少或抑制耕作（免耕）可能有潜力将碳固定在土壤中，这有助于减缓全球变暖。另一方面，这种做法通过改变地表的物理性质，对区域气候也有直接影响。然而，这些生物地球物理效应仍然知之甚少。在这里，我们表明，免耕管理会增加夏季农田的地表反照率，而由此产生的冷却效应在炎热极端天气中会放大，从而降低热浪期间达到的峰值温度。我们使用一个区域气候模型来模拟免耕农业对地表反照率的观测效应，以及土壤蒸发的可能减少，来研究欧洲全面转向免耕农业的潜在后果。我们发现，在炎热的夏季，当晴朗天气条件使地表反照率对地球辐射平衡的影响更大时，农田反照率增加所带来的夏季冷却效应会被强烈放大。与作物残茬覆盖相关的蒸发减少倾向于抵消反照率引起的冷却，但在炎热的日子里，反照率效应是主导因素。对于热浪夏季，免耕实践获得的局部冷却效应约为 2°C。地表反照率变化对夏季温度的不对称影响为针对高影响事件而不是平均气候特征的气候工程措施开辟了新的途径。
