SCIENTISTS leading global research into climate change have set out a stark vision of how the world will change if humanity fails to tackle surging greenhouse gas emissions.

A report issued yesterday by the Intergovernmental Panel on Climate Change (IPCC) described how a warming world would threaten billions of people with thirst and malnutrition, endanger more than half of wildlife species with extinction and initiate a melting of the Greenland ice cap that could raise global sea levels by more than 22ft.

Such warnings have been heard before but never with so much scientific certainty. The IPCC’s report was based on 29,000 observations taken around the world and published in more than 500 peer-reviewed scientific papers.

Yesterday, Ban Ki-moon, the UN secretary-general, who unveiled the report in Valencia, Spain, said: “All humanity must now assume responsibility for climate change.”

Ban has just been on a trip to Antarctica and South America, where he saw melting glaciers and ice-shelves. He said: “I come to you humbled after seeing some of the most precious treasures of our planet threatened by humanity’s own hand.”

Yesterday Gordon Brown issued his own statement, calling on the world to “face up to the challenge of climate change”. The prime minister added: “Climate change poses an urgent challenge that threatens the environment but also international peace and security, prosperity and development.”

Brown is expected to give a keynote speech on climate change this week, recommitting Britain to supplying a fifth of its energy requirements from renewable sources from 2020. Previously government officials had said Britain would struggle to meet the target and lobbied to be allowed to used different statistics.

The IPCC report sets out a variety of climatic impacts, including likely temperature rises of up to 4C, or even 6C. It predicts that Arctic summer sea ice will disappear by 2080 and that weather patterns will change globally. Such changes could include heatwaves, droughts, an increase in heavy rain and more intense storms.

In Europe, rising temperatures could turn much of Spain, Italy and Greece into deserts. Northern Europe, including Britain, would face more floods, heatwaves and stronger storms. Much of Australia would become uninhabitable.

Rajendra Pachauri, chairman of the IPCC, said one of the biggest impacts would come through rising sea levels. The report said levels were already likely to rise by 15in to 55in over the next few decades because water expands as it warms.

"This is a very important finding, likely to bring major changes to coastlines, and inundating low-lying areas, with a great effect in river deltas and low-lying islands,” said Pachauri.

Over a longer period - centuries or even millennia - rising temperatures could melt the Greenland ice cap, raising sea levels by an extra 22ft.

The report was, however, not entirely bleak. It also said that humanity had the power to stave off the worst effects of global warming at relatively low cost - but only if action was taken in the next decade.

The report is designed to provide the scientific underpinning for the Bali conference on climate change, which opens on December 3.

This will involve talks between more than 180 governments over the UN climate convention and, in particular, an extension to the 1997 Kyoto Treaty, which aims to limit global greenhouse gas emissions.

Some believe it is too late to prevent catastrophe. Among them is James Lovelock, the scientist who created the Gaia hypothesis of a self-regulating Earth, which now underlies much of climate science.

In an interview with Rolling Stone magazine, published this week, he suggests it is pointless to “green” society when so much damage has been done. Lovelock, 84, predicts food shortages, wars over water and land and a population crash that could leave just 500m survivors of the current population of 6.6 billion.

Nightmare vision

How scientists on the Intergovernmental Panel on Climate Change believe Earth will be affected:

- The world has already warmed by an average 0.7C in the past century. Temperatures in polar regions have increased the fastest, with 5C rises in some areas.

- Another 1.3C of warming is inevitable because of greenhouse gases already released into the atmosphere.

- Alpine ski resorts will be left without snow and many rivers will dry up. In Africa up to 250m more people will suffer water shortages by 2020.

- Worldwide agriculture could be devastated, especially in parts of Africa and Asia where some crop yields could halve by 2020.

- Tidal flooding will increase. Global sea levels are rising by 3.1mm a year and accelerating. Most is due to warm water expansion.

- Emissions of CO2 - the main greenhouse gas - grew by 80% between 1970 and 2004. Its concentration in the atmosphere is the highest for 650,000 years.

- The amount of CO2 emitted by humans will rise by up to 90% by 2030 unless action is taken.

For full climate change report

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