The world is poised to overshoot the goal of limiting average global warming to 1.5 degrees Celsius, as for the first time, a three-year period, ending in 2025, has breached the threshold. And climate scientists are predicting devastating consequences, just as the world’s governments appear to have lost their appetite for tackling the emissions that are causing the warming.

The 1.5-degree target was set at the Paris climate conference a decade ago, at the insistence of more vulnerable nations, to forestall severe weather impacts and potential runaway warming that could lead to exceeding irreversible planetary tipping points. But climate scientists say that 10 years of weak action since mean that nothing can now stop the target being breached. “Climate policy has failed. The 2015 landmark Paris agreement is dead,” says atmospheric chemist Robert Watson, a former chair of the U.N.’s arbiters of climate science, the Intergovernmental Panel on Climate Change (IPCC).

Meanwhile, a picture of what lies ahead is becoming clearer. In particular, there is a growing fear that climate change in the future won’t, as it has until now, happen gradually. It will happen suddenly, as formerly stable planetary systems transgress tipping points—thresholds beyond which things cannot be put back together again.

“We are rapidly approaching multiple Earth system tipping points that could transform our world with devastating consequences for people and nature,” says British global-systems researcher Tim Lenton, of the University of Exeter. If he and other scientists are right, then hopes currently being expressed of a temperature reset by reducing emissions after overshoot may be fanciful. Before we know it, there may be no way back.