A world without cars, planes, ships and factories powered by fossil fuels would have to become a reality in the next 40 years, to have a realistic hope of keeping global warming below safe levels, scientists say.

Researchers used climate simulations to predict the fate of the planet under different fossil fuel scenarios.

They found there was a 64 per cent chance of pegging global warming below the critical threshold of 1.5C above pre-industrial levels - but only if a massive programme to rid the world of fossil fuels started now.

Under this scenario, petrol and diesel-driven cars, aircraft and ships run on fossil fuels, and carbon-emitting power plants and factories would have to become history over a period of four decades.

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They would need to be replaced by zero-carbon alternatives such as electric cars, modern-style sailing vessels and renewable energy sources.

A big question mark hangs over the future of commercial air travel.

Currently, there is no practical alternative to kerosene aviation fuel, despite experiments involving solar powered flight and hydrogen.

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Delaying action until 2030 reduced the chances of keeping a 1.5C lid on global warming to below 50 per cent, the scientists said, writing in the journal Nature Communications.

Global warming above 1.5C increases the likelihood of dangerous impacts such as severe droughts and sea levels high enough to flood coastal cities.

But even the radical programme of fossil fuel phase-out outlined in the new study relies on no large-scale climate "tipping points" being breached in the coming decades

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Crossing tipping points such as the melting of polar permafrost or the sudden release of methane trapped on the ocean floor could put the Earth into a warming spiral from which there is no escape.

Under the 2015 Paris Agreement, world leaders pledged to limit global warming to 2C above pre-industrial levels and "pursue efforts" to achieve a lower target of 1.5C.

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"This is important information, as it shows that whether global mean temperature increase will be kept to below 1.5C depends on societal choices made today and emissions reductions implemented over the coming decades," the authors of the new study, led by Dr Christopher Smith from the University of Leeds, wrote.