That came with the Intergovernmental Panel on Climate Change’s “Special Report on Global Warming of 1.5 Degrees Celsius,” published in 2018, which gave rise to the climate strikers and the protest group Extinction Rebellion and breathed oxygen into the Sunrise Movement and the Green New Deal. Even those concerned on the sidelines had a clearer sense of just how short the timeline really was: that to avoid really dangerous warming required cutting global emissions almost in half by 2030. We are now halfway through that period, and emissions are higher than they were when the report was published.
The report also collated an entire scientific literature about the two warming levels, which has only grown since. Between 1.5 degrees and 2 degrees, it is estimated, more than 150 million people would die prematurely from the air pollution produced by the burning of fossil fuel responsible for that level of warming. Around the world, flooding events that used to arrive once a century, typically marking local cultures or even whole civilizations for generations, would instead strike annually — and in some places more often than that. Going from 1.5 degrees to 2 degrees, most scientists believe, would be a death sentence for the world’s coral reefs. And many believe that, in that range, the planet will lock in the permanent loss of many of its ice sheets, which could bring, over centuries, enough sea level rise to redraw the world’s coastlines.
If warming grows beyond those levels, so will its impacts. At 3 degrees, for instance, New York City could be hit by three 100-year flooding events each year and more than 50 times as many people in African cities would experience conditions of dangerous heat, as Bloomberg recently summarized. Wildfires would burn twice as much land globally, and the Amazon would cease to be a rainforest but a grassland. Potentially lethal heat stress, almost unheard of at 1.5 degrees, would become routine for billions at 2 degrees, according to one recent study, and above 3 degrees would impact places like the American Midwest.
In some ways, these projections may sound like old news, but as we find ourselves now adjusting to the possibility of a future shaped by temperature rise of that kind, it may be clarifying to recall that, almost certainly, when you first heard those projections, you were horrified. The era of climate reckoning has also been, to some degree, a period of normalization, and while there are surely reasons to move past apocalyptic politics toward something more pragmatic, one cost is a loss of perspective at negotiated, technocratic events like these.
Perhaps it was always somewhat fanciful to believe that it was possible to limit warming to 1.5 degrees Celsius. But as the writer and activist Bill McKibben has recently suggested, simply stating the goal did a lot to shape action in the years that followed — including by demanding that we all look squarely at what the science told us about what it would mean to fail. Five years on, for all the progress that has been made, those stakes are still the stakes.