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Burning the rest of the world's fossil fuels would lead to an 8C increase in global temperatures by 2300, scientists have estimated. Further to this, temperatures in the Arctic would rise by around 17C, while rainfall in the tropical Pacific could quadruple. Scientists warn that if mitigation measures are not taken to limit emissions from fossil fuels, climate changes will be "considerably more profound" than previously estimated.

A team of researchers led by Katarzyna Tokarska, from the University of Victoria in Canada, looked at what would happen if five trillion tonnes (5 EgC) of CO2 emissions were released – equivalent to the lower estimate of the world's remaining fossil fuels. Previously, simpler climate models showed there is a linear relationship between warming and CO2 emissions up to the release of two trillion tonnes, but beyond this, the relationship appears to break down.

Published in the journal Nature Climate Change, the team simulated long-term warming in response to the release of 5 EgC using four comprehensive models of Earth systems. Their findings showed that average global warming by 2300 will be between 6.4 and 9.5C higher than pre-industrial levels. This is far higher than simulations using less complex models, which indicated temperatures would rise by between 4.3 and 8.4C.

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They also said warming will be far greater in the Arctic: "Although the estimated ... global mean warming in response to 5 EgC emissions ranges from 6.4 to 9.5C, simulated warming considerably exceeds this in some regions, with mean Arctic warming ranging between 14.7 and 19.5C," they wrote.

The model also showed average precipitation will increase fourfold in the tropical Pacific, while it will halve in parts of Australia, the Amazon, southern Africa and the Mediterranean. Central Asia and North Africa will see a reduction in rainfall by a factor of three.

"Our results ... show that five trillion tonnes of cumulative carbon emissions, corresponding approximately to the unregulated exploitation of the fossil fuel resource, would result in considerably larger global and regional climate changes than previously suggested," they concluded. "Such climate changes, if realised, would have extremely profound impacts on ecosystems, human health, agriculture, economies and other sectors."