An international team of scientists has proposed a series of deadlines by which humanity must take serious action to combat climate change if it is to meet the ambitious goals of the 2015 Paris Agreement, and stave off potential disaster. The team behind the study hopes that these points of no return will help inform debate, and spur leaders to take action to mitigate the threat of climate change while there is still time.

In December 2015, 195 countries signed up to a legally-binding global climate deal known as the Paris Agreement. Signatories would work together to limit the increase in global average temperature to a total below 2 °C relative to pre-industrial levels, up to the year 2100. The agreement also set out an even more aspirational target of capping the rise in temperature to 1.5 °C by the end of the century.

The Paris goals were set in an attempt to mitigate the potential dangers posed by climate change. These include rising sea levels due to melting polar ice shields, and an increase in extreme weather events, such as droughts and flooding.

"In our study we show that there are strict deadlines for taking climate action," says Henk Dijkstra, a professor at Utrecht University in the Netherlands, and one of the study authors. "We conclude that very little time is left before the Paris targets [to limit global warming to 1.5°C or 2°C] become infeasible even given drastic emission reduction strategies."

The study is a joint effort between scientists from the Netherlands and the UK. The points of no return (PNR) set out in the new paper represent the thresholds after which it would be too late to take strong action on climate change with the hope of avoiding the worst of its effects. The team estimate that the thresholds have a 67 percent probability of being correct at this point.

The researchers used data from numerous climate models to define PNRs for the goals of the Paris Agreement, dependent in part on how quickly humanity can reduce emissions using renewable energy.

One set of PNRs deal with a moderate scenarios in which the share of renewable energy is increasing by 2 percent year on year from the point that serious action is taken. Another set of PNRs were calculated contingent on humanity increasing the share of renewable energy by 5 percent each year.

According to the results of the study, the PNR for using a moderate approach in the hope of keeping warming under 1.5 °C by the end of the century has already passed us by. However, if emissions could be cut by 5 percent each year, the governments of the world would have until 2027 to take extreme action.

For the more realistic target of capping warming to 2 °C by 2100, the moderate 2 percent scenario calls for action to be taken by 2035. If the share of renewable energy were to increase at a pace of 5 percent year on year, the PNR would be pushed back to 2045.

The authors also note that the PNRs could potentially be delayed by 6 to 10 years with the use of negative emissions technology, which remove greenhouse gasses already present in the atmosphere.

"We hope that 'having a deadline' may stimulate the sense of urgency to act for politicians and policy makers," concludes Dijkstra. "Very little time is left to achieve the Paris targets."

A paper detailing the findings has been published in the journal Earth System Dynamics.