The voluntary pledges made last year in the Copenhagen accord would only achieve 60 per cent of the emissions cuts required to head off the worst effects of global warming, the UNEP says. (Associated Press)

Emissions cuts pledged by countries in a nonbinding climate accord last year fall short of what's needed to avoid the worst consequences of global warming, the United Nations environment agency said Tuesday.

The sobering report by the UN Environmental Program comes as climate negotiators prepare for another round of talks next week in Cancun, Mexico.

Even if the voluntary pledges made last year in the so-called Copenhagen accord are fully met, that will only achieve 60 per cent of the emissions cuts required to keep temperatures from rising less than two degrees above pre-industrial levels and head off the worst effects of global warming, the UNEP said.

'There is a gap between the science and current ambition levels.'— Achim Steiner, UNEP

However, UNEP executive director Achim Steiner called those pledges "a good first step," and that the gap can be reduced further with steeper emissions cuts.

"There is a gap between the science and current ambition levels," Steiner said in a statement. "But what this report shows is that the options on the table right now in the negotiations can get us almost 60 per cent of the way there. This is a good first step."

The failure of the annual UN conference to produce a climate agreement last year in Copenhagen has raised doubts about whether the long-running, 194-nation talks can ever agree on a legally binding treaty for reining in global warming.

The core shortcoming has been in finding a consensus formula for mandatory reductions in countries' emissions of carbon dioxide and other global warming gases.

A dispute between the United States and China has stymied progress on this central element of any global climate deal.

Negotiators are not expected to solve that standoff in Cancun. Instead, delegates will focus on climate financial aid, deforestation and other secondary issues to try to revive momentum toward an umbrella deal at next year's conference in South Africa or at the Rio de Janeiro Earth Summit in 2012.

Eighty-five of the 140 countries that have associated themselves with the Copenhagen accord have pledged to cut emissions or rein in their growth by 2020, the report said.

If those pledges are fully met, global emissions levels would reach about 49 gigatons of carbon dioxide equivalent by 2020.

That's still five gigatons too high to have a chance to limit global warming to two degrees this century, Steiner said.

If none of the pledges made in Copenhagen are fulfilled, emissions would reach 56 gigatons, he said.

"[This report] is our contribution towards reminding the world of how far they would get with the decisions that they individually took in Copenhagen," Steiner told reporters during the launch of the report in Helsinki. "But also to point out that there is still a challenge that the world would have to address even if all of what was promised to each other in Copenhagen was implemented."