LONDON (Reuters) - Greenhouse gas emissions in 2020 could rise more than forecast to between 6 billion and 11 billion tons above what is needed to limit global warming to 2 degrees Celsius, a United Nations Environment Program (UNEP) report showed on Wednesday.
The gap between countries' emissions cut pledges and what is needed to remain under what scientists say is the limit to avoid devastating effects of global warming has widened since its 2010 estimate of 5-9 billion tons as new data emerged, UNEP said.
Extreme weather is likely to worsen across the globe this century as the Earth's climate warms, U.N. scientists warned last week, but global carbon emissions rose to a record level last year.
"To stay within the 2 degree limit, global emissions will have to peak soon (and) total greenhouse gas emissions in 2050 must be about 46 percent lower than their 1990 level, or about 53 percent lower than their 2005 level," the report said.
Countries agreed last year in Cancun, Mexico, that deep emissions cuts were needed to hold an increase in global average temperature below 2 degrees Celsius above pre-industrial levels.
Delegates from nearly 200 countries will meet in South Africa next week for a U.N. summit but only modest steps toward a broader climate deal are seen likely.
A 2 degrees C limit is only possible if emission levels are kept to around 44 billion tons of carbon dioxide equivalent in 2020. If nothing is done to limit emissions, they could rise to around 56 billion tons in 2020, UNEP said.
If countries' weakest pledges were implemented, emissions could recede to around 54.6 billion tons, leaving a gap of around 11 billion tonnes.
If nations make more ambitious pledges and U.N. climate talks adopt stricter rules on land use, forestry and surplus emissions credits, the figure could drop to around 50 billion tonnes, the report said.
Some scientists have warned emissions will have to peak before 2020 and fall to around 44 billion tonnes by 2020 to have a good chance of limiting temperature rise.
UNEP believes the emissions gap can be bridged by increasing energy efficiency and accelerating the deployment of renewable energy sources.
"There is abundant evidence that emissions reductions of between 14 to 20 billion tonnes ... are possible by 2020 and without any significant technical or financials breakthroughs," said Achim Steiner, UNEP's executive director.
"The window for addressing climate change is rapidly narrowing but equally the options for cost-effective action have never been so abundant," he said.
The report involved 55 scientists and experts across 15 countries.
Editing by Janet Lawrence