Ever since some of the earliest projections of climate change were made back in the 1970s, they have been remarkably accurate at predicting the rate at which global temperatures would rise. For decades, climate change has proceeded at roughly the expected pace, says David Armstrong McKay, a climate scientist at the University of Exeter, in England. Its impacts, however, are accelerating—sometimes far faster than expected.
For a while, the consequences weren’t easily seen. They certainly are today. The Southwest is sweltering under a heat dome. Vermont saw a deluge of rain, its second 100-year storm in roughly than a decade. Early July brought the hottest day globally since records began—a milestone surpassed again the following day. “For a long time, we were within the range of normal. And now we’re really not,” Allegra LeGrande, a physical-research scientist at Columbia University, told me. “And it has happened fast enough that people have a memory of it happening.”
In fact, a growing number of climate scientists now believe we may be careening toward so-called tipping points, where incremental steps along the same trajectory could push Earth’s systems into abrupt or irreversible change—leading to transformations that cannot be stopped even if emissions were suddenly halted. “The Earth may have left a ‘safe’ climate state beyond 1°C global warming,” Armstrong McKay and his co-authors concluded in Science last fall. If these thresholds are passed, some of global warming’s effects—like the thaw of permafrost or the loss of the world’s coral reefs—are likely to happen more quickly than expected. On the whole, however, the implications of blowing past these tipping points remain among climate change’s most consequential unknowns: We don’t really know when or how fast things will fall apart. [Continue reading…]