The Earth is quickly heading for the "point of no return" unless we act immediately, climate scientists have warned.

If governments don't act decisively on global warming before 2035, it will be very unlikely that we will be able to limit global warming to under two degrees, according to a major new study. If warming reaches over that point, it is likely to trigger climate catastrophe that could make much of the world unliveable.

The researchers also say that the deadline to stop global warming reaching 1.5C has already passed, unless we commit to radical action now. They hope that the strict deadline can become an important moment to commit to action on the climate.

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Without that action, Earth will fall past the point of no return and it will be impossible to stop global warming, they warn. And even those dramatic projects might be overly optimistic, they note.

"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."

All of the work depends on the world moving towards renewable energy sources in the coming years. To work out the deadline, researchers took available climate models and tried to understand how fast that process would need to happen to stem the disastrous effects that a 2C rise might have, calculating that we would have to begin meaningfully embracing renewable energy before 2035.

And the assumptions used to do that could be too optimistic, they noted.