Breaks in trends

摘要

Human influence on the climate system is clear~1. It is difficult, however, to establish robust links between the highly variable time series of global mean temperatures and specific human actions. Writing in Nature Geoscience, Estrada and colleagues~2 identify contributions from the two world wars and the Great Depression to early- and mid-twentieth-century cooling, and confirm swiftly rising anthropogenic greenhouse gas emissions from around 1960 as the onset of sustained global warming. Most intriguingly, they suggest that the emission limitations to ozone-depleting substances in the Montreal Protocol, as well as lower growth rates in atmospheric methane levels since the mid-1990s, played a role in the slow-down of warming over the past 15 years.