Billions of people across the world face hunger, severe water shortages and displacement as a result of increased temperatures, an international panel of scientists and politicians concluded yesterday.

In its second big report this year, the Intergovernmental Panel on Climate Change (IPCC) said that more extreme weather including hurricanes, typhoons, droughts and flooding was to be expected as a direct result of global warming.

The report, accepted by more than 100 national governments and designed to guide policymakers worldwide, gave warning that Britain and Europe could expect more heatwaves like that of 2003, which killed several thousand people in Paris.

It added that wildlife was likely to be devastated: a 3C rise in temperatures is predicted to make up to 30 per cent of all species extinct and a 5C rise up to 70 per cent. The report predicted that Africa, Asia, the Southern US and Southern Europe would suffer a crash in crop yields when temperatures rise by 2C, widely expected by the middle of the century. On the other hand, rises in summer temperatures combined with increased rainfall in parts of the Northern Hemisphere could bring improved crop performances. Britain and Northern Europe, Canada, and parts of the USA and Russia could, said Professor Martin Parry, who co-chaired the study, improve harvests by up to 15 per cent.

Hunger and malnutrition are predicted to be afflicting 500 million people by the end of the century. There are already 500 million people short of food, but improvements in farming and technology would cut that by half were it not for global warming, the panel said.

For the first time the IPCC accepted in its Impacts, Vulnerability and Adaptation Report for Policymakers that man-made climate change was having a global impact. When it last reported in 2001 it recognised limited regional consequences but this time it said that the evidence pointed towards impacts on a global scale.

Professor Parry said of the report’s conclusions: “What they have done is established that at a global level there is a man-made climate signal coming through in plants, animals and water supplies. This is the first time that we have confirmed this signal.”

Agreement did not come easily and the final session carried on through Thursday night into yesterday morning. Three scientists made formal complaints after delegates from the US, China, India, Saudi Arabia and Russia refused to accept a handful of their conclusions. Several scientific delegates walked out temporarily in protest at what they saw as political interference.

The panel foresees trees such as the horse chestnut and silver birch coming into leaf earlier in the season, patterns of bird migrations changing and alterations in insect distribution. It now agrees that physical effects such as the disappearance of the Chacaltaya Glacier in Bolivia are caused by man rather than localised and cyclical climate variations.

The areas expected to be worst affected are the Arctic, where the ice is predicted to melt over the next century, Sub-Saharan Africa, which will become even more arid, and the Asian mega-deltas, where extreme weather such as typhoons combined with sea-level rises are forecast to be devastating.

The panel said that the poorest people were those likely to be hit hardest but wildlife was predicted to fare even worse. Entire ecosystems would disappear as the ice melted in the Arctic and the permafrost in the Arctic retreats, it said.

The report has recognised for the first time that acidification is causing corals, already threatened by bleaching from warming temperatures, to dissolve. Mediterranean regions and mountain biodiversity are equally at threat, as are habitats such as salt marshes and mangrove swamps, and effects are already being felt as water temperatures in rivers and lakes warm up.

The report emphasised the importance of countering climate change through adaptation. The IPCC still wants mitigation measures, those designed to drag greenhouse gas emissions down, but it believes that adapting to new circumstances will be far more effective for the first half of the century.

Dr Tim Sparks, an environmental scientist at the Centre for Ecology and Hydrology, welcomed the IPCC’s recognition that climate change was already having an impact. He said of the report: “If ever there was an alarm bell, then this is it. The authors give dire warnings, such as extinctions of a quarter of the Earth’s species, unless we . . . act to reduce harmful emissions into the atmosphere.”