Published on Dec 6, 2017
This is a video abstract for Brown and Caldeira (2017) published in Nature
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 percent 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 percent chance that the world would have warmed on average by more than 4°C 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 percent chance that global warming will—once again, under the business-as-usual scenario—exceed 4°C by 2100.
And since the world’s nations met in Paris in 2015 and agreed to keep overall global warming to “well below” 2°C, even that figure represents “dangerous” global warming. One degree higher would count as “catastrophic.” And a rise of beyond 5°C would deliver the world into an unknown and unpredictable period of change.
Two U.S. scientists reported in the journal Nature that they went back to the climate models used as the basis for forecasts made by the UN’s Intergovernmental Panel on Climate Change and then matched the reasoning against observations.