Nations have the chance to deliver almost 60 per cent of the emissions reductions needed to keep global temperatures under a 2 degrees Celsius rise.
But only if the pledges made last year in Copenhagen are fully met.
These are among the findings of a new report compiled by the UN Environment Programme (UNEP) and jointly authored by over 30 leading scientists from numerous international research institutes.
The report was convened in conjunction with the European Climate Foundation and the National Institute of Ecology-SEMARNAT, Mexico.
The findings, launched in advance of the UN climate convention meeting in Cancun, Mexico, spotlight the size of the 'emissions gap' between where nations might be in 2020 versus where the science indicates they need to be.
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 ground to curb emissions. There is no time to waste. By closing the gap between the science and current ambition levels, we can seize the opportunity to usher in a new era of low-carbon prosperity and sustainable development for all.'
It is estimated that, in order to have a 'likely' and cost-effective chance of pegging temperatures to 2 degrees Celsius or below over the 21st Century, global emissions will need to have peaked within the next 10 years and be around 44 gigatonnes of CO2 equivalent in 2020.
The report, whose compilation was led by the UNEP Chief Scientist, finds that:
- Under a business-as-usual scenario, annual emissions of greenhouse gases could be around 56 gigatonnes of CO2 equivalent by 2020. As a point of reference, global emissions were estimated to be around 48 gigatonnes in 2009;
- Fully implementing the pledges and intentions associated with the Copenhagen Accord could, in the best case identified by the group, cut emissions to around 49 gigatonnes of CO2 equivalent by 2020;
- This would leave a gap of around 5 gigatonnes of CO2 equivalent that needs to be bridged over the coming decade-an amount equal to the emissions of all the world's cars, buses and trucks in 2005;
- In the worst case identified in the report - where countries follow their lowest ambitions and accounting rules set by negotiators are lax rather than strict - emissions could be as high as 53 gigatonnes in 2020, only slightly lower than business as usual projections.