Cutting emissions by 2020 to a level that could keep a global, 21st century, temperature rise under 2 degrees C is technologically and economically feasible, says a comprehensive new study released Wednesday by the UN Environment Programme (UNEP).

Accelerated uptake of renewable energy, fuel switching and energy efficiency improvements can deliver a large slice of the necessary cuts.

Other measures include sectoral improvements ranging from increased penetration of public transport and more fuel efficient vehicles to ones in areas, such as, agriculture and waste management.

The report cites aviation and shipping as a special but important case, as currently these 'international emissions' fall outside the Kyoto Protocol-the emission reduction treaty.

Together they account for around five per cent of C02 emissions and could account for up to 2.5 Gigatonnes (Gt) of carbon dioxide equivalent (GtCO2e) annually, by 2020.

"Options for reducing emissions from both sectors include improving fuel efficiency and using low-carbon fuels. For the shipping sector, another promising and simple option is to reduce ship speeds," says the report which has involved 55 scientists and experts from 28 scientific groups across 15 countries.

The Bridging the Emissions Gap report, issued just days ahead of the UN climate convention negotiations in South Africa and seven months before the Rio+20 summit in Brazil, provides the clearest indicators yet that the world already has the solutions to avert damaging climate change.

It presents policymakers with clear ideas on how to bridge the emissions gap by 2020 which, as a result of improved modeling from last year's assessment, is now estimated, under the most optimistic scenarios, to be 6 GtCO2e rather than 5 Gt of GtCO2e.

The report also outlines far more pessimistic scenarios, if the commitments and pledges of developed countries, including levels of financing amounting to $100 billion a year by 2020, and the intentions of developing ones are not fully realized-the gap then, by 2020, could be 11 GtCO2e. Under business-as-usual conditions, it could even be 12 GtCO2e.