There is a “very high risk” that the most ambitious global warming limit set in the Paris climate agreement is likely to be exceeded by the 2040s, according to a draft United Nations (UN) report.

Only a dramatic and unprecedented shift away from fossil fuels will enable world governments to limit warming to 1.5C above pre-industrial times, it said.

Hitting this target would “involve removal of carbon dioxide from the atmosphere,” said the report compiled by scientists on the UN’s Intergovernmental Panel on Climate Change (IPCC).

Sent out for comments from governments and experts this week, a copy of the current draft report was obtained by Reuters.

Questioned about its contents, the IPCC said it did not comment on the contents of draft reports while work is on-going as “the text can change substantially” between the current draft and the final version.

Changes could still be made as a result of feedback from reviewers and additional research findings published after the current draft was completed. The final version is due to be released in October.

As part of the Paris agreement, the decision was made to “pursue efforts to limit the temperature increase to 1.5C above pre-industrial levels”.

In total, 195 countries signed the accord and 173 have become party to the document which aims to curb global carbon emissions and contain global warming.

However, US President Donald Trump withdrew the US from the agreement last year, claiming it put American workers – particularly in the coal industry – at an “economic disadvantage".

10 photographs to show to anyone who doesn't believe in climate change Show all 10 1 /10 10 photographs to show to anyone who doesn't believe in climate change 10 photographs to show to anyone who doesn't believe in climate change A group of emperor penguins face a crack in the sea ice, near McMurdo Station, Antarctica Kira Morris 10 photographs to show to anyone who doesn't believe in climate change Floods destroyed eight bridges and ruined crops such as wheat, maize and peas in the Karimabad valley in northern Pakistan, a mountainous region with many glaciers. In many parts of the world, glaciers have been in retreat, creating dangerously large lakes that can cause devastating flooding when the banks break. Climate change can also increase rainfall in some areas, while bringing drought to others. Hira Ali 10 photographs to show to anyone who doesn't believe in climate change Smoke – filled with the carbon that is driving climate change – drifts across a field in Colombia. Sandra Rondon 10 photographs to show to anyone who doesn't believe in climate change Amid a flood in Islampur, Jamalpur, Bangladesh, a woman on a raft searches for somewhere dry to take shelter. Bangladesh is one of the most vulnerable places in the world to sea level rise, which is expected to make tens of millions of people homeless by 2050. Probal Rashid 10 photographs to show to anyone who doesn't believe in climate change Sindh province in Pakistan has experienced a grim mix of two consequences of climate change. “Because of climate change either we have floods or not enough water to irrigate our crop and feed our animals,” says the photographer. “Picture clearly indicates that the extreme drought makes wide cracks in clay. Crops are very difficult to grow.” Rizwan Dharejo 10 photographs to show to anyone who doesn't believe in climate change Hanna Petursdottir examines a cave inside the Svinafellsjokull glacier in Iceland, which she said had been growing rapidly. Since 2000, the size of glaciers on Iceland has reduced by 12 per cent. Tom Schifanella 10 photographs to show to anyone who doesn't believe in climate change A river once flowed along the depression in the dry earth of this part of Bangladesh, but it has disappeared amid rising temperatures. Abrar Hossain 10 photographs to show to anyone who doesn't believe in climate change A shepherd moves his herd as he looks for green pasture near the village of Sirohi in Rajasthan, northern India. The region has been badly affected by heatwaves and drought, making local people nervous about further predicted increases in temperature. Riddhima Singh Bhati 10 photographs to show to anyone who doesn't believe in climate change A factory in China is shrouded by a haze of air pollution. The World Health Organisation has warned such pollution, much of which is from the fossil fuels that cause climate change, is a “public health emergency”. Leung Ka Wa 10 photographs to show to anyone who doesn't believe in climate change Water levels in reservoirs, like this one in Gers, France, have been getting perilously low in areas across the world affected by drought, forcing authorities to introduce water restrictions. Mahtuf Ikhsan

Although the agreement aimed to keep global temperatures “well below” 2C above pre-industrial times, the more ambitious target of 1.5C is seen as the best way to avoid the harmful impacts of climate change.

These include devastating natural disasters such as droughts and flooding, which are increasingly being directly linked with rising temperatures.

The negative impacts that could be avoided if the world sticks to the more ambitious goal were recently outlined in the Climatic Change journal.

“We know that the 1.5C target is challenging,” said Professor Nigel Arnell, a climate scientist at the University of Reading who led that study.

He added that it told us "that if we achieve this target then we can avoid between 60 and 95 per cent of the adverse impacts of climate change than we could otherwise see.”

The IPCC report was commissioned to determine the likelihood of hitting these temperature targets.

Previous research has suggested the 1.5C goal is unlikely, with some predicting it could be exceeded within the coming decade.

The draft report states that there has been no historical precedent for the kind of changes required in energy use to keep global temperatures below the target limit.

Renewable energy sources will have to rapidly replace fossil fuels and carbon dioxide will have to be actively removed from the atmosphere.

This kind of removal would require the roll-out of carbon capture and storage technologies and potentially the planting of forests to absorb carbon dioxide.

“If the final version of the new IPCC Special Report should, in October, reach the conclusion that there is high risk of breaching the 1.5C limit by mid-century, that would be no surprise,” said Dr Phillip Williamson, a UK Natural Environment Research Council scientist who has been invited to review the current draft of the report, but has not yet seen the document.

He noted the IPCC conclusions are drawn from and therefore consistent with published scientific literature concerning projected future greenhouse gas emissions.

The most optimistic of these predictions suggest targets of between 1.5C and 2C might still be possible.

However, even these will require an “overshoot” – a period in the coming decades when global temperatures rise beyond those limits, only to be brought down again.

Climate change is 'defining threat of our time', says UN Secretary General

However, Dr Williamson also acknowledged that commenting on reporting of the leaked draft is “fraught with difficulties”.

Other climate scientists also echoed the IPCC in their statement that the final report will likely differ from the current version.

“The report is incomplete and findings can change substantially so I don’t think too much should be read into the statements,” said one of the report’s authors Professor Piers Forster, a climate change scientist at the University of Leeds.

“The IPCC review process is very transparent and rigorous. We expect to get many thousands of review comments on this draft and will need to respond to each one carefully.”

He added that the report as it stands, served as a reminder of how to countries should be approaching climate change.

“With regard to what measures might be implemented to avoid such a situation, the answer is straightforward: every country needs to stop adding to the problem, by increasing the urgency of effort to reduce greenhouse gas emissions,” said Dr Williamson.