“Keep 1.5 alive.” For years, that phrase has been the rallying cry for climate advocates. Enshrined in the 2015 Paris climate accord, the 1.5-degree Celsius figure is the world’s aspirational limit for average global temperature rise. For those well versed in climate science, it serves as a shorthand for avoiding the worst consequences of climate change—the threats to nearly every aspect of human life that stem from rising global temperatures. Behind the 1.5-degree veil await more destructive storms, catastrophic coastal flooding, rampant hunger and disease, extreme and deadly heat waves, and the demise of the world’s remaining coral reefs.
But the 1.5-degree slogan does not adequately convey these threats. It communicates one figure about climate change—the average increase in global temperature since preindustrial times—and assumes knowledge of climate dynamics that most people lack. It fails to convey both the enormity of the stakes and the narrow window for corrective action. The Intergovernmental Panel on Climate Change (IPCC), the UN-sponsored body of scientists and economists that periodically assesses the science and risks of climate change, calculates that global greenhouse gas emissions must fall by 60 percent by 2035 (from 2019 levels) to limit global warming to 1.5 degrees.
