THE world will warm by 3C (5.4F) even under emissions projections for 2050 that leading scientists consider optimistic, the United Nations group that studies global warming has said.

The increase, which would cause drought and famine for 400 million people and devastate wildlife, is predicted by the Intergovernmental Panel on Climate Change (IPCC) in its most confident assessment yet of how greenhouse gases are affecting global temperatures.

A draft of part of the panel’s fourth report, which the US Government has released on the internet, shows that it has, for the first time, placed a likely figure on the progress of global warming, indicating a level of scientific certainty that it has avoided in the past.

It says that temperatures could increase by between 2C and 4.5C when atmospheric carbon dioxide reaches double the pre-industrial level, but it declares 3C to be the “most likely value” for such change. A 3C rise is the level at which a Met Office conference last year judged that “dangerous” climate change would occur. Previous reports from the IPCC, a traditionally cautious body, have given only wider ranges of possibilities, which it acknowledged to be highly uncertain.

While the panel does not indicate when this rise will occur, experts think it probable that pre-industrial carbon dioxide levels will double by 2050, even given successful efforts to contain greenhouse gas emissions.

Sir David King, Britain’s chief scientific adviser, has argued that stabilisation of carbon dioxide at this level — 550 parts per million — is the best target that the world can hope for, and his view is endorsed by many climatologists.A report issued by Sir David last month suggested that a 3C rise would put 400 million people at risk of starvation because of lost arable land and water shortages.

As the figure is a global average larger increases could be expected in areas such as the South East of England, where a 4.5C increase could bring 25 per cent more rainfall in winter and 60 per cent less in summer. More extreme weather is also predicted, and rising sea levels would leave many coastal areas at risk of flooding.

The draft document is the report of the IPCC’s Working Group I, which examines the physical science basis for climate change. The analysis of Working Groups II and III, which consider detailed consequences and mitigation strategies, have not been released.

Its contents came to light yesterday when the journal Nature reported that the United States had published the draft on a website, inviting comments from experts and other interested groups. The unusual manner of its release has alarmed some scientists and environmental groups, who questioned whether the Bush Administration was seeking to defuse its bold conclusions before the final version is published in February.

Roger Pielke Jr, of the University of Colorado, told Nature: “If the report is already out there in circulation, then the ‘news’ value is likely to be much diminished when the official report is finally released.” Friends of the Earth said that the US Government had repeatedly tried to undermine the IPCC in the past.

Apart from providing the most precise estimates yet of the likely course of climate change, the document’s language is much more confident than that of the IPCC’s third report published in 2001. It points to decisive new evidence that the rising temperatures recorded over the past 50 years are the result of human activity and not natural variation. The pattern of warming ocean, surface and lower atmosphere temperatures, with melting ice at the poles and falling temperatures in the stratosphere, now make it “highly unlikely (less than 5 per cent)” that natural changes could be responsible.

Catherine Pearce, of Friends of the Earth, said: “The implications of a 3C rise give a greater increase in urgency. What we need to see is reinforcement of the current EU target of 2C.”

CLIMATE CHANGE FINDINGS

• The document is a draft version of the IPCC’s Working Group I, which is considering the underlying science of climate change
  
  
• The rise in temperature when atmospheric carbon dioxide reaches twice its pre-industrial levels is likely to be from 2C to 4.5C. The “most likely value” is 3C. Values higher than 4.5C “cannot be excluded”, but do not correspond well with the data
  
  
• Climate change at present is “highly unlikely” to be the result of natural variability
  
  
• Global average temperatures have increased by about 0.65C since 1900, up from the 0.6C estimate in last report
  
  
• The world faces future global warming of at least 0.1C per decade even if all greenhouse emissions were to end today
  
  
• The IPCC report will be finalised at a meeting next month and published next year. It will also contain two other reports into mitigation strategies and likely consequences, details of which have yet to be released
  
  
• Details of how to access the whole report can be found at: www.climatescience.gov/Library/ipcc/wg14ar-review.htm

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