There is a 95% chance that even concerted global efforts to tackle climate change won't help the planet stay within 2C warming this century.
A forecast of likely warming trends and emissions for the rest of the century has found that there is only a very slim chance that we will stay within 2C by 2100. It is published in the journal Nature Climate Change.
"Countries argued for the 1.5C target because of the severe impacts on their livelihoods that would result from exceeding that threshold," study author Dargan Friers of the University of Washington said in a statement.
"Indeed, damages from heat extremes, drought, extreme weather and sea level rise will be much more severe if 2C or higher temperature rise is allowed. Our results show that an abrupt change of course is needed to achieve these goals."
Anything more ambitious than the 2C target is looking increasingly difficult. There is only a 1% chance of meeting the more ambitious 1.5C target set in the Paris Agreement. To put the challenge in perspective, if we all stopped burning all fossil fuels immediately, we would more likely than not experience warming of 1.3C by the end of the century.
"Our analysis shows that the goal of 2 degrees is very much a best-case scenario," said lead author Adrian Raftery, a UW professor of statistics and sociology. "It is achievable, but only with major, sustained effort on all fronts over the next 80 years."
The study took into account the world's growing population, GDP per person and the amount of carbon emitted per dollar of economic activity, simulating more or less ambitious efforts to tackle the problem.
Part of the challenge is that the world's population is likely to hit 11 billion by 2100. However, the growing population is likely not to have a very large impact on carbon emissions. This is because the greatest population growth is expected in Africa. At the moment, Africa is the least carbon-intensive continent. Assuming that continues, the large population growth won't have a huge impact on climate change.
All those factors considered, the most likely figure for warming is about 3.2C by 2100, the study finds.
"Our analysis is compatible with previous estimates, but it finds that the most optimistic projections are unlikely to happen," Raftery said. "We're closer to the margin than we think."