Atmospheric aerosols affect the Earth's climate in many ways, including acting as the seeds on which cloud droplets form. Since a large fraction of these particles is anthropogenic, the clouds' microphysical and radiative characteristics are influenced by human activity on a global scale leading to important climatic effects. The respective change in the energy budget at the top of the atmosphere is defined as the effective radiative forcing due to aerosol-cloud interaction (ERF_aci). It is estimated that the ERF_aci offsets presently nearly 1/4 of the greenhouse-induced warming, but the uncertainty is within a factor of two. A common method to calculate the ERF_aci is by the multiplication of the susceptibility of the cloud radiative effect to changes in aerosols by the anthropogenic change of the aerosol concentration. This has to be done by integrating it over all cloud regimes. Here we review the various methods of the ERF_aci estimation. Global measurements require satellites' global coverage. The challenge of quantifying aerosol amounts in cloudy atmospheres are met with the rapid development of novel methodologies reviewed here. The aerosol characteristics can be retrieved from space based on their optical properties, including polarization. The concentrations of the aerosols that serve as cloud drop condensation nuclei can be also estimated from their impact on the satellite-retrieved cloud drop number concentrations. These observations are critical for reducing the uncertainty in the ERF_aci calculated from global climate models (GCMs), but further development is required to allow GCMs to properly simulate and benefit these novel observables.

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基于卫星的云介导气溶胶强迫估计的前沿

大气气溶胶以多种方式影响地球气候，包括充当云滴形成的种子。由于这些颗粒大部分是人为产生的，因此云的微物理和辐射特性受到全球范围内人类活动的影响，从而导致重要的气候影响。大气顶部能量收支的相应变化被定义为气溶胶-云相互作用引起的有效辐射强迫（ERF _aci）。据估计，ERF _aci目前抵消了近 1/4 温室引起的变暖，但不确定性在两倍以内。计算 ERF _{aci 的}常用方法是将云辐射效应对气溶胶变化的敏感性乘以气溶胶浓度的人为变化。这必须通过将其集成到所有云体系中来完成。在这里我们回顾一下 ERF _aci估计的各种方法。全球测量需要卫星的全球覆盖。本文综述的新方法的快速发展解决了量化多云大气中气溶胶量的挑战。可以根据气溶胶的光学特性（包括偏振）从太空检索气溶胶特性。作为云滴凝核的气溶胶的浓度也可以根据它们对卫星检索的云滴数浓度的影响来估计。这些观测对于减少根据全球气候模型 (GCM) 计算出的 ERF _aci的不确定性至关重要，但需要进一步发展，以允许 GCM 正确模拟并受益于这些新的观测数据。