The world is on course to exceed global warming limits set out in the Paris climate agreement much earlier than previously thought, scientists have warned, following the first comprehensive study of the impact of melting permafrost.

Experts said dangerous climate change was almost “inevitable” and the planet was on the brink of a “tipping point” as thawing permafrost releases large volumes of carbon dioxide and methane into the atmosphere, causing temperatures to rise and more permafrost to melt.

They warned that governments were engaged in “wishful thinking” when it came to emission reductions and said their study showed previous warming projections that failed to account for permafrost thaws may be inaccurate.

Permafrost – soil that has been frozen for at least two years – acts as a store for large amounts of carbon and other nutrients from organic matter.

However, governments have largely failed to factor the release of vast amounts of carbon held in this frozen rock and sediment into their climate projections.

Researchers at the International Institute for Applied Systems Analysis, who studied the impact of thawing permafrost on emissions targets, said policymakers had made assumptions about climate change based on a “linear relationship” between global temperature rise and CO2 emissions.

They found that the release of huge amounts of carbon would render past emissions projections useless as they fail to account for the exponential growth triggered by melting permafrost.

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Lead author Thomas Gasser said his study was the first time such a tipping process was adequately accounted for in emission budgets.

According to the researchers, doing so shows that the world is closer to exceeding the budget for the long-term target of the Paris Agreement than previously thought.

“The scientific answer to ‘how soon are we likely to exceed our Paris target’ is somewhere between 10 years ago and the next 20 years. Definitely not later than that,” he told The Independent.

“We should have changed course a while ago, and we should now significantly increase our efforts to do so.”

He added: “Permafrost carbon release from previously frozen organic matter is caused by global warming, and will certainly diminish the budget of CO2 we can emit while staying below a certain level of global warming.

“It is also an irreversible process over the course of a few centuries, and may therefore be considered a ‘tipping’ element of the Earth's carbon-climate system that puts the linear approximation of the emission budget framework to the test."

The Paris Agreement commits signatories to limit global warming to no more than 2C above pre-industrial temperatures – with a further aim of keeping the increase to 1.5C – by the end of the century.

The deal acknowledges that the 1.5C target will initially be exceeded, peaking at “well below” 2C and then pursuing efforts to get back to 1.5C.

However Mr Gasser described that approach as the "lazy solution” and warned it relied on “hypothetical technology, and a lot of wishful thinking”.

He said: "Overshooting is a risky strategy and getting back to lower levels after an overshoot will be extremely difficult.

“However, since we are officially on an overshooting trajectory, we have to prepare ourselves for the possibility that we may never get back to safer levels of warming.”

Commenting on the study, Bob Ward, policy director at the London-based Grantham Research Institute on Climate Change, said: “This important study shows how dangerous it could be for the world to trigger the tipping point beyond which thawing permafrost releases large volumes of carbon dioxide and methane into the atmosphere.

“If this happens, it could become inevitable that we suffer dangerous climate change. That is why it is so vital that global emissions of carbon dioxide and other greenhouse gases from human activities are cut strongly and urgently to limit the amount of further global warming and avoid reaching such a disastrous tipping point.”