Pledges made by countries to reduce greenhouse gas emissions under the Copenhagen Accord will deliver less than two-thirds of the cuts needed to stop global temperatures rising by more than 2°C, new analysis showed yesterday.

The study suggests that fully implementing the voluntary agreement hammered out in the dying hours of last December’s UN climate talks could deliver just under 60 per cent of the cuts needed to tackle “dangerous” climate change.

It is estimated that, for it to be “likely” temperatures will not rise by more than 2°C, emissions need to peak in the next decade and fall to 44 billion tons (gigatons) by 2020.

The report, coordinated by the UN Environment Programme (Unep), found that if no action was taken to curb the emissions which cause global warming, annual output would grow from current levels of about 48 gigatons to 56 gigatons in 2020.

Fully implementing the pledges by countries and blocs such as the EU, the US and China which signed up to the Copenhagen Accord, including the most ambitious proposals in cases where countries put forward a range of options, could cut emissions to around 49 gigatons by 2020.

That would leave a gap of around five gigatons ­– equivalent to the emissions of all the world’s cars, buses and lorries in 2005 – which would have to be bridged by more ambitious action to cut carbon and tackle other greenhouse gases such as methane from rubbish tips, Unep executive director Achim Steiner said.

But the report also warned that if countries followed their least ambitious pledges and were “lenient” in the way they count emissions reductions, the world could end up with emissions as high as 53 gigatons – not much lower than the “business as usual” scenario. The UN climate talks in Copenhagen last December were widely regarded as having ended in failure because they did not achieve the original aim of securing a new, legally-binding deal on cutting emissions and providing money for poor countries to cope with global warming. World leaders who had gathered in the Danish capital for the UN summit ended up negotiating a voluntary accord under which countries offered to curb their emissions with the aim of limiting temperature rises to 2°C above pre-industrial levels.

Yesterday, Mr Steiner, who is also UN Under-Secretary General, insisted the pledges on the table under the Copenhagen Accord were a “good first step” to combating climate change.

Ahead of the next major UN climate meeting, which starts in Cancun, Mexico, next week, he said: “The results indicate that the UN meeting in Copenhagen could prove to have been more of a success than a failure if all the commitments, intentions and funding, including fully supporting the pledges of developing economies are met.”

Mr Steiner said: “There is a gap between the science and current ambition levels. 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 study, led by Unep, was compiled by more than 30 researchers from countries around the world, including the UK.

Last year’s Copenhagen Accord was not negotiated through the official UN process and was merely “noted” by the conference as a whole, amid frantic scenes in the early hours of the last day of the summit.

Christiana Figueres, the UN’s top climate official, said: “The report underlines both the feasibility of emissions reductions and the importance of international cooperation to raise the current inadequate level of ambition.

“Governments meeting at the UN climate conference in Cancun will need to both anchor the pledges they made in Copenhagen in the UN context and to work swiftly to agree ways to reduce emissions so that the world has a chance of staying below a 2°C temperature rise.”

And UN Secretary General Ban Ki-Moon said: “I encourage all parties to make good on their national mitigation pledges, and to further progress within the negotiations as well as through strengthened efforts on the curb emissions.”

Joseph Alcamo, Unep chief scientist, said that the current range of ambition in the pledges to take action could lead to the world becoming between 2.5°C and 5°C warmer by the end of the century – while a “business as usual” scenario could see global temperatures rise by 7°C above pre-industrial levels.

Mr Steiner said there were opportunities in a number of sectors to find more emissions cuts, for example by removing billions of pounds worth of “perverse” subsidies which encouraged the use of fossil fuels.