Delaying action on climate change will only increase costs and reduce options for dealing with its worst effects, according to a draft report by UN experts.

A final-draft report by the intergovernmental panel on climate change was obtained by the Associated Press news agency on Thursday.

It warns that global warming will continue to increase unless countries cut emissions and shift quickly to clean energy.

The panel said that emissions of carbon dioxide and other greenhouse gases that are warming the planet grew yearly by an average of 2.2 per cent between 2000 and 2010, compared to 1.3 per cent per year from 1970 to 2000.

Unless "explicit efforts" are made to reduce greenhouse gas emissions, the experts warn that increased conservation and efficiency will not be sufficient to counter the rise.

They project emissions from the sector will double or triple by 2050 from the 2010 level unless improvements in clean energy are "significantly accelerated."

International climate negotiators agreed at the UN's 2009 Copenhagen climate change conference that global warming this century must increase by less than two degrees to avoid the worst impact of climate change.

Scientists say that target requires atmospheric concentration of carbon dioxide to stay below 530 parts per million.

The report warned that to stay below that level throughout the 21st century would require a reduction in greenhouse gas emissions of between 40 and 70 per cent of 2010 levels by 2050 - requiring transformation to a low-carbon economy.