evidence: Air temperatures on Earth have been rising since the Industrial Revolution. While natural variability plays some part, the preponderance of evidence indicates that human activities—particularly emissions of heat-trapping greenhouse gases—are mostly responsible for making our planet warmer. According to an ongoing temperature analysis led by scientists at NASA’s Goddard Institute for Space Studies (GISS), the average global temperature on Earth has increased by at least 1.1° Celsius (1.9° Fahrenheit) since 1880. The majority of the warming has occurred since 1975, at a rate of roughly 0.15 to 0.20°C per decade. [...] The leveling off of temperatures in the middle of the 20th century can be explained by natural variability and by the cooling effects of aerosols generated by factories, power plants, and motor vehicles in the years of rapid economic growth after World War II. Fossil fuel use also increased after the war (5 percent per year), boosting greenhouse gases. Cooling from aerosol pollution happened rapidly. In contrast, greenhouse gases accumulated slowly, but they remain in the atmosphere for a much longer time. According to former GISS director James Hansen, the strong warming trend of the past four decades likely reflects a shift from balanced aerosol and greenhouse gas effects on the atmosphere to a predominance of greenhouse gas effects after aerosols were curbed by pollution controls.