The ban on emissions of ozone-depleting substances under the Montreal Protocol led to a detectable slow-down in climate warming since the 1990s, concludes an article published online this week in Nature Geoscience. The findings help to link human actions over the past century with changes in the rate of warming, using a statistical method independent of global climate models.
Francisco Estrada and colleagues identified changes in the rate of warming and in the rate of increase in the concentrations of greenhouse gases in the atmosphere between 1880 and 2010, using statistical analyses. Because these changes coincide, they conclude that changes in the warming rate can be attributed to specific human actions that affected greenhouse gas concentrations. The findings point to a slow-down in warming during the two world wars and the Great Depression, when emissions were reduced in response to economic downturns. The authors also highlight a slow-down in the 1990s in response to the Montreal Protocol, which initiated the phasing out of CFCs — substances that not only harm the ozone layer but are also potent greenhouse gases. The analysis further reveals a pronounced rise in both temperature and greenhouse gas concentrations in the 1960s, which marks the onset of sustained global warming.
In an accompanying News and Views article, Felix Pretis and Myles Allen note that the study suggests “that past changes in the rate of warming can be directly attributed to human influences, from economic downturns to the regulations of the Montreal Protocol.”