The climate science update, prepared by British Met Office scientists, found that the increase this century could top 15 degrees above pre-industrial levels in the Arctic and be up to 10 degrees for parts of Africa.

In Australia, rainfall is projected to decline by at least one-fifth along parts of the coastline, worsening drought.

The Met Office Hadley Centre's head of climate impacts, Richard Betts, said the most severe scenarios outlined in the 2007 Intergovernmental Panel on Climate Change report now looked conservative.

"We've always talked about these very severe impacts only affecting future generations, but people alive today could live to see a 4-degree rise," Dr Betts told The Guardian.

Where the panel said a probable scenario without action to stop emissions was 4 degrees of warming by 2100, the new report says that level could be reached by 2060 in an extreme case.

The warning came as more than 2000 officials from about 190 countries met in Bangkok for the start of two weeks of climate talks crucial to shaping December's prospective Copenhagen agreement.

Analysts hold little hope of significant progress in Thailand after world leaders offered few concrete proposals at last week's meetings in the US.

Green and welfare groups expressed frustration yesterday after it was revealed that the G20 leaders' meeting in Pittsburgh watered down a climate-change communique at the last minute.

The Age understands proposals about a funding plan to help poorer countries reduce emissions and adapt to the effects of climate change were removed.

An earlier draft said rich nations needed to substantially increase spending to help the poor cope. It also stressed the importance of carbon markets and said oversight should be increased.