The world's nations must urgently ramp up commitments to cut planet-warming carbon emissions to avoid "human tragedy", the United Nations warned yesterday.

As they stand, these commitments - which do not kick in until 2020 - would still allow average global temperatures to climb as high as 3.4C by the end of the century, a recipe for massive climate damage, the UN Environment Programme (UNEP) said in its annual Emissions Gap report.

"If we don't start taking additional action now, beginning with the upcoming climate meeting in Marrakesh, we will grieve over the avoidable human tragedy," said UNEP head Erik Solheim.