Delaying action on global warming will only increase the costs and reduce the options for dealing with the worst effects of climate change, according to a draft report by UN experts.
The final draft of the report by the Intergovernmental Panel on Climate Change, obtained on Thursday by The Associated Press, says that global warming will continue to increase unless countries shift quickly to clean energy and cut emissions.
It said that despite national policies and international efforts aimed at mitigating climate change, emissions of carbon dioxide and other greenhouse gases that are warming the planet grew 2.2 per cent per year on average between 2000 and 2010, compared with 1.3 per cent per year from 1970 to 2000.
The two main drivers for the increasing emissions are economic growth, which has risen sharply, and population growth, which has remained roughly steady, the report said.
The largest contributor to global emissions results from the burning of oil and coal - and the draft report said its contribution is expected to rise.
Unless "explicit efforts" are made to reduce greenhouse gas emissions, the experts warned that increased conservation and efficiency will not be sufficient to counter their rise.
With increasing demand for energy and the growing use of coal to generate electricity, the experts said emissions from the sector are projected to double or triple by 2050 from the level in 2010 unless improvements in clean energy are "significantly accelerated".
International climate negotiators agreed at the 2009 UN climate change conference in Copenhagen that global warming this century must increase by less than 2C to avoid the worst impacts of climate change.
Scientists say that target requires atmospheric concentration of carbon dioxide, the main greenhouse gas, to stay below 530 parts per million. The level recently surpassed 400 parts per million.
The report said the majority of scenarios to stay below 530 parts per million throughout the 21st century would require a reduction in greenhouse gas emissions between 40 per cent and 70 per cent of 2010 levels by 2050.
The experts said this will require new patterns of investment and a transformation into a low-carbon economy.
The global total annual investment in the energy system is presently about $US1.2 trillion ($A1.36 trillion), it said.
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