The United Nations Environment Program (UNEP) said Tuesday that countries will have to be far more ambitious in cutting greenhouse gas emission if the world is to effectively curb a rise in global temperature at 2 degrees Celsius or less.

In its Year Book 2010 released on the sidelines of the 11th Global Ministerial Environment Forum and the Chemical Ministerial Convention at Nusa Dua of Bali province, the UNEP said that annual global greenhouse gas emissions should not be more than 40 to 48.3 Giga tons (GT) of equivalent CO2 in 2020 and should peak sometime between 2015 and 2021.

The report also estimated that between 2020 and 2050, global emission need to fall by between 48 and 72 percent, indicating that an ambition to cut greenhouse gases by around 3 percent a year over the 30 years' period is also needed. "Such a path offers a 'medium' likelihood or at least a 50/50 chance of keeping a global temperature rise at below 2 degrees Celsius," said the report.

It also said that the expected emissions for 2020 range between 48.8 to 51.2 GT of CO2 equivalent should be fulfilled. In order to meet the 2 degrees Celsius aim in 2050, emissions in 2020 need to be between 40 and 48.3 Gt.

Thus, the report said, even with the best intentions, there is a gap between 0.5 and 8.8 GT of CO2 equivalent per year, amounting to an average shortfall in emission cuts of 4.7 GT.

Achim Steiner, the UN Under-Secretary General and the UNEP Executive Director, told journalists that the report provided an indication of where countries are and perhaps more importantly where they need to aim. "The 'Giga ton gap' needs to be bridged quickly if the national community is to pro-actively manage emissions down in a way that makes economic sense," said Steiner, adding that more delay in taking action, more cost would be.