As world leaders converge on Paris Monday to begin a much-anticipated round of climate change talks, it will be only the 21st session of the conference of the parties to the U.N.’s climate-change framework treaty. But the world has worried about climate change and its effects for far longer. The hole in the ozone layer brought the issue into focus for many non-experts in the 1980s, but scientists have been aware that the Earth’s climate is changing—and that human actions can affect that change—for over a century. During the first industrial revolution, increased use of fuels like coal coincided roughly with the discovery of the role of atmosphere in regulating climate.