When major new climate change scenarios are released, there’s always strong interest. These scenarios lay out what our future climate will look like, depending on how fast we act to cut emissions.
But what was surprising about the seven new scenarios announced last week was that United States President Donald Trump took an interest. Why? Because a high-emissions scenario – known as RCP8.5 and its successor SSP5-8.5 – had been removed. Under these worst-case scenarios, nations would make no effort to cut emissions and expand fossil fuel use. By 2100, carbon dioxide levels would almost triple, to 1,135 parts per million, and the world would be around 4.5°C hotter than the pre-industrial period.
The climate scientists responsible for laying out the range of possible futures removed the RCP8.5 scenarios for a very good reason. Although often slow and incomplete, our efforts to tackle climate change have made a tangible difference. We have averted the worst climate future once thought possible.
The job is far from done. Emissions are at record highs, and global warming is speeding up. But the removal of this high-emissions scenario isn’t, as Trump and other climate sceptics have claimed, a sign of failed modelling, or that climate change was a hoax. It’s a sign that the expansion of solar, wind, electric vehicles and batteries has slowed emissions growth.
Many climate impacts are becoming evident after about 1.4°C of warming – the level we’re roughly at now. Because this period of extremely rapid climate change is due to human activities, it means we also have the opportunity to shape the future.
A group of scientists has created scenarios representing a range of possible climate futures. They base them on what’s happened so far and what might happen in politics and technology over the coming decades. Then they select the emissions pathways deemed most plausible and then sample a range of different futures, which are more or less optimistic about our fossil fuel use.
None of the new scenarios are as pessimistic as RCP8.5/SSP5-8.5. The worst possible scenario now envisions high emissions leading to warming of around 3.5°C by 2100. That would still be very, very bad.
Climate sceptics leapt on the removal of RCP8.5 as a sign the projections were wrong. These attacks were not made in good faith, but to cast doubt on climate science. A clear-eyed assessment is that RCP8.5 was removed because climate action is starting to work.
But while the worst outcome has been averted, we have also missed the window for the best future climate. The new scenarios have no pathway as optimistic as the lowest emissions scenario from the last round. Because global emissions haven’t yet begun to fall, the most optimistic new pathway would lead to warming peaking at about 1.9°C.
Our current emissions trajectory is somewhere in the middle. Based on current policies and countries’ actions, we’re looking at around 2.6°C warming by 2100. Taking RCP8.5 off the table is a sign of progress – we’ve avoided the worst-case scenario. But we have also missed the best-case future.