Current pledges from rich and developing nations for cutting carbon pollution will stoke potentially catastrophic warming by century's end, according to a study released yesterday on the eve of the Copenhagen climate summit.
National commitments proposed so far for the December 7-18 UN conference would mean the global temperature would rise by 3.5 degrees Celsius over pre-industrial times, way over a 2.0˚C threshold widely considered safe, the study said.
The study said concentrations of carbon dioxide (CO₂) would hit about 650 parts per million (ppm), according to the tally published by the Potsdam Institute for Climate Impact Research in Germany and energy specialists Ecofys.
"The pledges on the table will not halt emissions growth before 2040, let alone by 2015 as indicated by the IPCC [the UN's Intergovernmental Panel on Climate Change] and are far from halving emissions by 2050 as has been called for by the G8," said Niklas Hoehne of Ecofys.
"Instead, global emissions are likely to be nearly double 1990 levels by 2040 based on present pledges."
The Copenhagen conference gathers the 192-member UN Framework Convention on Climate Change (UNFCCC). Its task is to craft a global pact that will dramatically reduce man-made carbon emissions - invisible gases that trap solar heat and warm the atmosphere, interfering with Earth's delicate climate system.
Mr Hoehne said that pledges by developed countries so far were currently projected to be 13 to 19 per cent below 1990 levels. But forest credits that these countries are likely to claim against their emission target would lower this contribution by around five per cent.
The IPCC, the UN's panel of climate scientists, says cuts of around 25-40 per cent reductions by industrialised countries by 2020 from 1990 levels would be needed to achieve the 2˚C target.
For developing countries, emissions cuts of 15 to 30 per cent by 2020 against "business-as-usual" scenarios are needed to avoid crossing the 2˚C (3.6˚F) threshold.
Voluntary promises by China to make gains in energy efficiency and vows, also non-binding, by Brazil and Indonesia to tackle deforestation, will be a big help, said the paper.
Overall, developing country emissions are projected to be close to the IPCC range, it added.
In contrast, a report issued yesterday by climate economist Nicholas Stern and the UN Environment Programme (UNEP) concluded that closing the "emissions gap" could be somewhat easier than thought.
"Existing proposals from developed and developing countries constitute a big step towards a level consistent with the 2˚C (3.6˚F) goal," which would require that CO₂ emissions stay under 44 billion tonnes in 2020, their report said.
"Taking countries' highest intentions would take the world to around 46 billion tonnes (of carbon)," meaning that only a two-billion-tonne shortfall would have to be bridged.
To achieve this, though, "would require governments over the next two weeks and over the next few years to match words with deeds, and ambition with actions," Mr Stern said.
"If they do, we could embark on the most dynamic and creative period of the world's economic history, a new energy and industrial revolution."