Improving our fundamental understanding of the role of aerosol-cloud interactions in the climate system Proceedings of the National Academy of Science of the United States

The effect of an increase in atmospheric aerosol concentrations on the distribution and radiative properties of Earth's clouds is the most uncertain component of the overall global radiative forcing from preindustrial time. General circulation models (GCMs) are the tool for predicting future climate, but the treatment of aerosols, clouds, and aerosol-cloud radiative effects carries large uncertainties that directly affect GCM predictions, such as climate sensitivity. Predictions are hampered by the large range of scales of interaction between various components that need to be captured. Observation systems (remote sensing, in situ) are increasingly being used to constrain predictions, but significant challenges exist, to some extent because of the large range of scales and the fact that the various measuring systems tend to address different scales. Fine-scale models represent clouds, aerosols, and aerosol-cloud interactions with high fidelity but do not include interactions with the larger scale and are therefore limited from a climatic point of view. We suggest strategies for improving estimates of aerosol-cloud relationships in climate models, for new remote sensing and in situ measurements, and for quantifying and reducing model uncertainty.

大气气溶胶浓度升高对地球云系分布与辐射特性的影响，是工业化前全球总辐射强迫（radiative forcing）中不确定性最高的组成部分。通用环流模式（General Circulation Models, GCMs）是预测未来气候的核心工具，但当前对气溶胶、云系以及气溶胶-云辐射效应的处理存在显著不确定性，这些不确定性直接影响GCM的预测结果，例如气候敏感度。气候预测的开展受到阻碍，原因在于各组分间相互作用的尺度跨度极大，且这些尺度均需被精准捕捉。观测系统（遥感（remote sensing）、原位测量（in situ））正越来越多地被用于约束气候预测，但目前仍存在诸多显著挑战：部分原因在于尺度跨度大，且各类测量系统往往仅针对特定尺度开展观测。精细尺度模式能够以高保真度表征云系、气溶胶以及气溶胶-云相互作用，但无法涵盖大尺度相互作用，因此从气候研究视角而言存在局限性。本研究提出了多项改进气候模式中气溶胶-云关系估算的策略，同时为新型遥感与原位测量方案、量化并降低模式不确定性的路径提供了参考方向。