By the time they reach retirement age, the changes will be far more dramatic — and perhaps life-threatening on a massive scale, an authoritative U.N. study will say this week.

On Monday, the Intergovernmental Panel on Climate Change, a network of more than 2,000 scientists, opens a five-day meeting in Brussels, Belgium, to finalise a report on how warming will affect the globe and whether humans can do anything about it.

The panel will paint a bleak picture of increasing poverty, paucity of drinking water, melting glaciers and polar ice caps, and a host of vanishing species by mid-century unless action is taken to curb emissions of carbon dioxide and other heat-trapping gases.

Some regions like parts of North America and northern Europe will see some benefits, at least in the short term, from longer growing seasons and milder winters.

Even the most optimistic forecasts say the climate will continue to change and the planet will be irrevocably damaged. The question is, how much?

``We are going into a realm the Earth has not seen for a very long time ... over the past 800,000 years,'' said Camille Parmesan, a University of Texas biologist who has studied the effects of climate change on wildlife and was a reviewer of the upcoming report.

A draft of the IPCC's summary has been obtained by the Associated Press, but policy makers will go over the document line-by-line this week before unveiling the final text on Friday.

It will then become a guideline for Governments to determine policies and draft legislation.

About 285 delegates from 124 countries are attending, along with more than 50 of the scientists who compiled the report and dozens of observers from non-government, mostly environmental, organisations.

The closed-door talks are likely to focus on predictions of how many people will be at high risk from changing ecosystems and water cycles, and whether such specific weather events like Hurricane Katrina should be attributed to global warming. — AP