LONDON - The world can still prevent global temperatures from rising more than two degrees Celsius by doing far more than current pledges to reduce harmful emissions, a UN report released on Wednesday said.

The report, titled Bridging the Emissions Gap, has been prepared by the UN Environment Programme (UNEP) with scientists and experts from 28 scientific groups across 15 countries.

According to the report, global emissions of greenhouse gases should not be higher than 44 billion tons of its carbon dioxide equivalent by 2020 to limit temperature rises to under two degrees this century.

This means there is a shortfall of 6 billion tons even if all the most ambitious pledges by individual countries are combined.

However, the gap can be bridged if more efforts are made to produce energy from non-fossil fuel sources such as biomass and renewable energy, and if emissions of other greenhouse gases apart from carbon dioxide are also reduced.

The task is "technologically and economically feasible", said Joseph Alcamo, the chief scientist of UNEP.

Commenting on the findings of the report, UN Secretary-General Ban Ki-moon said lots remained to be done in terms of ambition and policy.

"But it also shows that the gap can still be closed if we act now. This is a message of hope and an important call to action," he added.

UNEP Executive Director Achim Steiner said the report "puts into the hands of governments and policymakers vital information about their options if the world is to meet the climate change challenge."

The report will be discussed next week in Durban, South Africa at the UN Framework Convention on Climate Change. Its executive secretary Christiana Figueres said the main challenge for governments would be agreeing on the immediate future of the Kyoto Protocol and working to define a global, binding climate agreement.