The Great Depression, World Wars I and II and an international treaty restricting ozone-depleting chemicals each had measurable effects on global temperatures, scientists report November 10 in Nature Geoscience. This finding represents one of the first times scientists have linked specific economic and political events to observed changes in how fast global temperatures are rising.
As greenhouse gas emissions soared over the last century, Earth’s temperature also rose, though not always at a constant rate. The planet’s average surface temperature grew steadily from 1910 to around 1940, cooled slightly until around 1970 and then shot up until 1998. In the last 15 years, the warming has slowed but not stopped, most climate researchers agree (SN: 10/5/13, p. 14). These shifts have both natural and human causes. But scientists have struggled to pinpoint the exact factors responsible for any particular change in Earth’s warming rate.