College of Engineering, Mathematics, and Physical Sciences, University of Exeter, Exeter, UK.
Met Office Hadley Centre, Exeter, UK.
Nature. 2017 Jun 22;546(7659):485-491. doi: 10.1038/nature22974.
Aerosols have a potentially large effect on climate, particularly through their interactions with clouds, but the magnitude of this effect is highly uncertain. Large volcanic eruptions produce sulfur dioxide, which in turn produces aerosols; these eruptions thus represent a natural experiment through which to quantify aerosol-cloud interactions. Here we show that the massive 2014-2015 fissure eruption in Holuhraun, Iceland, reduced the size of liquid cloud droplets-consistent with expectations-but had no discernible effect on other cloud properties. The reduction in droplet size led to cloud brightening and global-mean radiative forcing of around -0.2 watts per square metre for September to October 2014. Changes in cloud amount or cloud liquid water path, however, were undetectable, indicating that these indirect effects, and cloud systems in general, are well buffered against aerosol changes. This result will reduce uncertainties in future climate projections, because we are now able to reject results from climate models with an excessive liquid-water-path response.
气溶胶对气候具有潜在的重大影响，特别是通过它们与云的相互作用，但这种影响的幅度具有高度不确定性。大型火山爆发会产生二氧化硫，进而产生气溶胶；因此，这些爆发代表了一种通过定量气溶胶-云相互作用的自然实验。在这里，我们表明，2014-2015 年冰岛霍拉洪拉火山大规模裂隙喷发减小了液滴云的大小——这与预期一致——但对其他云特性没有明显影响。液滴尺寸的减小导致云变亮，2014 年 9 月至 10 月全球平均辐射强迫约为-0.2 瓦特/平方米。然而，云量或云液水路径的变化无法检测到，这表明这些间接影响，以及一般的云系统，对气溶胶变化有很好的缓冲作用。这一结果将降低未来气候预测的不确定性，因为我们现在能够拒绝对具有过多液水路径响应的气候模型的结果。
