Tomorrow may experience a hotter world than anyone had feared. Global warming, under the notorious “business-as-usual scenario” in which humans go on burning fossil fuels to power economic growth, could by 2100 be at least 15% warmer than the worst UN projections so far. And the spread of uncertainty in such gloomy forecasts has been narrowed as well.

Climate scientists had worked on the assumption that there was a 62% chance that the world would have warmed on average by more than 4°C [39.2 F] if no action was taken to reduce greenhouse gas emissions.

But a new study has not only raised the stakes, it has narrowed the uncertainty. There is now a 93% chance that global warming will – once again, under the business-as-usual scenario – exceed 4°C by 2100.

And since, in Paris in 2015, the world’s nations met and agreed to keep overall global warming…