By environment correspondent Alex Kirby

Scientists say rising global temperatures will condemn millions to hunger this century.

In a United Nations report, they say agricultural production will decline in Asia and Africa, while Australia and New Zealand will become short of water.

Europe will face a higher flooding risk, and the eastern seaboard of the US may expect more storm surges and coastal erosion.

And the harder climate change bites, the likelier it is that profound and possibly irreversible changes will occur.

The scientists are members of the Intergovernmental Panel on Climate Change (IPCC), a UN body bringing together many of the world's leading climatologists.

Last month the IPCC published a report on the science of climate change, saying the world was warming faster than previously predicted, and there was increasingly strong evidence for humanity's influence on the climate.

Snapshot

It said world temperatures this century could rise by between 1.4 and 5.8 degrees Celsius. Sea levels could also rise by tens of centimetres, threatening millions of people in low-lying countries.

Hunger in Asia is predicted to worsen

This report is on the impacts of climate change, the Earth's vulnerability to them, and the prospects for adaptation.

The IPCC was launched in 1988 by the World Meteorological Organisation and the UN Environment Programme (Unep).

This is its strongest and most detailed warning so far of the impact of global warming.

The director of Unep, Dr Klaus Toepfer, said of the latest report: "The scientists have shown us a compelling snapshot of what the Earth - which already faces so many other social and environmental pressures - will probably look like later in the 21st century.

"We must start helping vulnerable species and ecosystems to adapt to new climate conditions."

Signs

The executive secretary of the UN climate change convention, Michael Zammit Cutajar, said: "The report has powerful implications for how we deal with poverty and sustainable development over the coming decades."

The report says many of the physical changes that scientists expect are visible today:

• the extent of Arctic sea ice has shrunk by 10-15%, while Antarctic sea ice retreated south by 2.8 degrees latitude from the mid-1950s to the early 1970s
• Alaska's boreal forests are expanding northwards at about 100 km (62 miles) for every one degree Celsius rise
• ice cover on lakes and rivers in the mid to high northern latitudes now lasts for about two weeks less than it did in 1850
• in Europe, some Alpine plants are migrating upwards by from one to four metres every decade, and between 1959 and 1993 the growing season in gardens lengthened by nearly 11 days
• in the northern hemisphere, migratory birds are arriving earlier and staying later.

The IPCC says there will be damage across the world - less rain, spreading deserts, risks to food supplies, more storms and floods, and an increase in infectious diseases like malaria and dengue fever.

Some Alpine plants are moving upwards

It says small island states will be among the countries most seriously affected, and developing countries everywhere will have difficulty in adapting.

There will be some beneficial effects: an increased global timber supply, bigger crop yields in some countries, more water in some areas like south east Asia, and fewer deaths from cold in the winter.

Positive feedbacks

But the IPCC warns that "projected climate changes during the 21st century have the potential to lead to future large-scale and possibly irreversible changes".

These include slowing of the system that transports warm water to the north Atlantic, large ice losses in Greenland and the West Antarctic, and the release of carbon and methane as the Earth heats up.

The likelihood of these changes is "probably very low", the report says. "However, their likelihood is expected to increase with the rate, magnitude and duration of climate change."