Greenhouse gas emissions are on track to be far above the levels needed by 2020 to limit global temperature rises to 2C, experts are warning.
Without a rapid scaling-up of action, current pledges by governments to curb emissions by 2020 will put the world on a path to temperature rises of between 3C and 5C this century, the United Nations Environment Programme (UNEP) warned.
And the gap between projected emissions by 2020 and the levels which can give countries a chance of meeting the agreed target to limit temperature rises to 2C has widened, the latest report from UNEP warned.
A large proportion of the world's CO2 emissions comes from burning fossil fuels
The emissions gap report, which comes ahead of the start of the latest round of international climate talks in Doha, Qatar, found that greenhouse gas levels are currently 14% above what they need to be in 2020.
If countries carry on without taking action on climate change, emissions are set to be 58 gigatonnes in 2020, compared to the 44 gigatonnes level at the end of the decade that it is estimated will put the world on track to meet the 2C target.
Countries have agreed they want to curb temperature rises to 2C to try and stop the most dangerous impacts of climate change.
At the chaotic UN climate talks in 2009 in Copenhagen nations put forward voluntary pledges to curb emissions by 2020, while last year's conference resulted in an agreement to negotiate a new legally-binding deal by 2015 which would come into force by 2020.
But UNEP's report on Wednesday warned that even if countries meet the most ambitious pledges they have made to tackle emissions this decade under the strictest rules, the gap between actual emissions and what is needed by 2020 will be 8Gt.
The figure is 2Gt more than in the last report in 2011.
UNEP's latest assessment paints a bleaker picture than previous reports in 2010 and 2011 partly as a result of projected economic growth in key developing countries and "double counting", for example where both a rich country funding a carbon-cutting scheme such as a wind farm and a poor country where it is taking place claim credit for reductions.
But while UNEP said action needed to be scaled and speeded up without delay, the environmental organisation said bridging the gap by 2020 was still feasible, with potential for measures in areas such as transport, building and forestry.
Putting off action on emissions until after 2020 will push up the costs of keeping temperature rises to 2C by around 10% to 15%, economic analysis in the report shows.
UNEP executive director Achim Steiner said the transition to a low-carbon, inclusive green economy was happening far too slowly and the opportunity to meet the 44Gt target was narrowing with each year.
He warned: "The world has already broken the speed limit in carbon dioxide and is still putting its foot down on the pedal even though it knows a T-junction is ahead."
But he cautioned against the idea that the 2C target was unachievable and the world should reconcile itself to much higher temperature rises over the next century.
"I believe this report challenges this kind of fatalism. It's perfectly feasible for the world to stay within a 2C scenario," he said.
The report outlines the opportunity for 17Gt of potential emissions savings that could be implemented within this decade, which bridge even the widest gap between projected emissions levels and the 44Gt target.
These include introducing building codes which include energy efficiency standards, implementing vehicle efficiency standards and public transport schemes and taking steps to prevent deforestation, for example by increasing protected forest areas.
There are examples of such policies being introduced in a number of countries, where they also have other benefits such as reducing energy costs and cutting air pollution.
Experts have called for protected areas of rainforest to be expanded to help soak up CO2
But Niklas Holme, director of energy and climate policy at UNEP, warned: "We now have one year less to close the gap.
Even if it had remained at the same level it would be more difficult to close it because we have lost one year to implement measures."
Responding to the UNEP report, energy and climate change secretary Ed Davey said: "The UNEP report shows that the world needs to go further and faster in cutting emissions to keep global warming below 2C.
"While the report is clear that bridging the emissions gap remains feasible, the growing gap highlights the urgent need for additional and effective action to reduce emissions.
"We're working hard in the UK to shift to a low carbon economy and I'll be pressing for action in the forthcoming global climate change talks in Doha, especially on those countries who have yet to make pledges.
"I will also be pushing complementary initiatives in the energy and forestry sectors and looking to reduce gases such as HFCs".
Next week the government is set to publish its long-awaited Energy Bill which aims to secure billions of pounds investment needed to build new low-carbon power supplies in the UK.
But the run-up to the publication of the Bill has seen divisions emerge in the Cabinet over backing for low-carbon power against support for more gas plants, whether to include a target to decarbonise the power sector by 2030 and even suggestions that the UK could row back on laws tackling climate change.
Mr Steiner said: "The UK has passed legislation, set itself targets for emissions reductions, it would be surprising to the international community if the UK were not to adhere to its own targets which were not imposed from outside but taken by a sovereign parliamentary decision."
He added that developing countries, who were sceptical about how much action richer nations were actually taking to tackle climate change, would be watching developed countries and it was crucial those such as the UK took the lead.
Keith Allott, WWF-UK's head of climate change, said: "Six years ago, on his famous trip to the Arctic, David Cameron pledged leadership on climate change.
"The world has never been in more need of such leadership, yet Mr Cameron has lost his voice on the issue both at home and internationally.
"The prime minister urgently needs to prove to the world, and to the UK public, that he has not gone cold on climate change - and that he can be the leader he promised to be."
Commenting on the report, Bob Ward, policy and communications director at the Grantham Research Institute on Climate Change and the Environment at London School of Economics and Political Science, said: “If the world is to have a reasonable chance of avoiding a rise in global average temperature of more than 2C, global emissions of greenhouse gases need to peak within the next few years and fall to about 44bn tonnes by 2020.
"With the United Nations Framework Convention on Climate Change due to review the 2C target from next year, with a view to strengthening it to 1.5C, there may be some who argue for a relaxation on the basis that there is a lack of political will. This would be extremely short-sighted and risky. Choosing a target of, say, 3C would mean we aim for a global average temperature that has not been seen on Earth for about three million years, when the polar ice sheets were much smaller and global sea level was 15 to 25 metres higher than today.
"Governments should think very carefully about whether today’s generation really does not have the will to prevent their children, grandchildren and future generations from facing the huge risks that would result from a return to a prehistoric climate.”
Kaisa Kosonen, climate policy adviser at Greenpeace International, said the UNEP report followed warnings from the World Bank, the CIA and international investors over climate change.
"But the most important message that the UNEP report delivers is that we can still keep warming below dangerous levels.
"At the climate talks in Doha, governments can and must maintain a robust international process free from loopholes.
"Beyond Doha, governments and business must focus on redirecting investments from fossil fuels to renewable energy and efficiency."
Friends of the Earth's international climate campaigner, Asad Rehman, said: "This report is a stark warning that cannot be ignored - nations must take urgent and comprehensive action to slash emissions to avert a climate disaster.
"The clock is ticking but there's still time to act - countries meeting in Doha next week must agree a clear course of action to tackle climate change before it is too late.
"Developed nations like Britain must show leadership by getting themselves off the fossil fuel hook and securing the new jobs and economic benefits that building a low-carbon economy will bring."