With global warming currently standing at approximately +1.2 °C since pre-industrial times, climate change is a pressing global issue. Marine cloud brightening is one proposed method to tackle warming through injecting aerosols into marine clouds to enhance their reflectivity and thereby planetary albedo. However, because it is unclear how aerosols influence clouds, especially cloud cover, both climate projections and the effectiveness of marine cloud brightening remain uncertain. Here we use satellite observations of volcanic eruptions in Hawaii to quantify the aerosol fingerprint on tropical marine clouds. We observe a large enhancement in reflected sunlight, mainly due to an aerosol-induced increase in cloud cover. This observed strong negative aerosol forcing suggests that the current level of global warming is driven by a weaker net radiative forcing than previously thought, arising from the competing effects of greenhouse gases and aerosols. This implies a greater sensitivity of Earth’s climate to radiative forcing and therefore a larger warming response to both rising greenhouse gas concentrations and reductions in atmospheric aerosols due to air quality measures. However, our findings also indicate that mitigation of global warming via marine cloud brightening is plausible and is most effective in humid and stable conditions in the tropics where solar radiation is strong.

自前工业化时代以来，全球变暖目前约为+1.2°C，气候变化是一个紧迫的全球问题。海洋云增亮是一种通过向海洋云中注入气溶胶以增强其反射率从而提高行星反照率来解决变暖问题的方法。然而，由于尚不清楚气溶胶如何影响云，特别是云量，气候预测和海洋云增亮的有效性仍然不确定。在这里，我们利用夏威夷火山喷发的卫星观测来量化热带海洋云上的气溶胶指纹。我们观察到反射阳光大幅增强，这主要是由于气溶胶引起的云量增加。观察到的强烈负气溶胶强迫表明，目前的全球变暖水平是由比之前认为的更弱的净辐射强迫驱动的，这是由温室气体和气溶胶的竞争效应引起的。这意味着地球气候对辐射强迫更加敏感，因此对温室气体浓度上升和空气质量措施导致的大气气溶胶减少产生更大的变暖反应。然而，我们的研究结果还表明，通过海洋云增亮来缓解全球变暖是可行的，并且在太阳辐射较强的热带地区潮湿和稳定的条件下最为有效。