The European Union's goal of keeping the global temperature rise to 2C is unlikely to be met, a leading climate researcher has warned.
The IPCC report warns of declining crop yields and increased hunger
Professor Martin Parry told BBC News that millions, if not tens of millions, would be at increased risk to their lives from a rise above 2C (3.6F).
Professor Parry co-chairs the impacts working group of the Intergovernmental Panel on Climate Change (IPCC).
The group's full 2007 report is being presented to scientists in London.
Its summary findings were unveiled in April.
Asked what the chances were of keeping the average global temperature rise at or below 2C, Professor Parry said: "Quite little, I think, unfortunately.
"And it's evident from the work of the IPCC that even with a maximum of 2C we're not going to avoid some major impacts at the regional level."
His personal estimate was that the rise could be constrained to between 2C and 3C.
Adapt and survive
The IPCC report on Impacts, Vulnerability and Adaptation paints a picture in sober scientific language of a world where some regions see significant changes as greenhouse gas levels and average temperatures escalate.
Parts of Africa would see water shortages, as would Asian and South American zones fed by mountain glacier melt.
Crop yields would decline across the tropics; Europe would see an increase in heatwaves.
But Professor Parry said steps could be taken to help societies adapt to these impacts.
"We need to talk very seriously about major amounts of adaptation being put in place now," he said.
The Kyoto Protocol established mechanisms which would leverage money for adaptation from carbon trading. But the funds have been criticised as being too small and too bureaucratic, and there have been wrangles over who controls them.
A number of development agencies including Britain's Department for International Development (DfID) are seeking to build climate adaptation into their aid projects.
Speaking at the London IPCC meeting, held at the Royal Geographical Society (RGS), Trade and Development Minister Gareth Thomas described climate change as a "development challenge".
"Failing to tackle it will lead to floods, droughts and natural disasters which can destroy poor people's lives as well as their livelihoods," he said.
"If we want to achieve the aspirations of the Make Poverty History campaign or the targets of the Millennium Development Goals, we - governments, citizens and developing countries themselves - must rise to the challenge."