THE world is heading for an average temperature rise of nearly 4C, according to an analysis of national pledges from around the globe. Such a rise would bring a high risk of major extinctions, threats to food supplies and the near-total collapse of the huge Greenland ice sheet.

More than 100 heads of state agreed in Copenhagen last December to limit the rise in global temperatures to 1.5C-2C above the long-term average before the industrial revolution, which kickstarted a huge global increase in the greenhouse gases thought to trigger climate change.

But six months on, a major international effort to monitor the emission reduction targets of more than 60 countries, including all the major economies, the Climate Interactive Scoreboard, calculates that the world is on course for a rise of nearly double the stated goal by 2100.

Another study, by Climate Analytics, at the Potsdam Institute in Germany, suggests there is “virtually no chance” world governments will keep the temperature rise below 2C, and it is likely to be 3.5C by the end of the century.

In both analyses the current commitments suggest a much better outcome than the estimated business-as-usual temperature rise of 4.8C, but it is well above the 2C maximum the UN hoped would be agreed this December in Cancun, Mexico.

In its last assessment of the problem, in 2007, the Intergovernmental Panel on Climate Change (IPCC) forecast that a rise of more than 2C would lead to potential increases in food production, but an increasingly high risk of extinction for 20-30 per cent of species, more severe droughts and floods, and a unstoppable “widespread to near total” loss of the Greenland ice sheet over very long time periods.

At 4C it predicted global food production was “very likely” to decrease, “major extinctions around the globe”, and near-total loss of Greenland's ice. The severity of floods, erosion, water pollution, heatwaves, droughts and health problems such as malnutrition and diarrhoeal diseases would also increase.

In a separate development, the first major independent review of criticisms of the global assessment of climate change led by the UN declared it had found “no errors that would undermine the main conclusions” of the IPCC that climate change will have serious consequences.

— The Guardian, London