"We're on a toboggan and we've gone over the edge," Tim Dyson, professor of population studies at the London School of Economics, told the gathering.

"It (global warming) will screw everyone up, no matter where you are," he said at the start of the four-day conference of 2,000 demographers, economists, geographers and sociologists from 110 countries.

Scientists predict global warming, caused mainly by increasing carbon dioxide emissions from the burning of coal, oil and petrol in motor vehicles and power stations, will increase the frequency and severity of droughts, flooding and storms, threatening global agricultural production.

The world scientific authority on global warming, the Intergovernmental Panel on Climate Change (IPCC), predicted in its 2001 report that rising levels of greenhouse gases like carbon dioxide will increase temperatures by between 1.4 degrees and 5.8 degrees Celsius (35 and 42 degrees Fahrenheit) by the end of the century and sea levels by between 9 and 88 centimetres (3.5 and 35 inches).

The IPCC, set to produce its next report in 2007, is likely to "increase its temperature estimates by 0.2 degrees (Celsius) at both the low and high end," Tim Dyson told the conference in this central French city.

He said that if per capita CO2 emissions remained at their 2000 levels, which he said was unikely, population increases would raise world emissions by 27 percent to 29.6 billion tons over the next 50 years.

World population is expected to reach nine billion in the next fifty years from 6.5 billion today.

Even a 40 percent reduction in per capita emissions in the developed world would be outweighed solely by the effects of demographic growth elsewhere in the world, Dyson said.

At the top end scenario, where emissions in the developing world double but remain constant in the industrialised countries, the increase in CO2 emissions would be 90 percent above 2000 levels by 2050.

Developed countries have so far been unable to reduce emissions, even in Europe where population is expected to fall in the next fifty years.

The United States, responsible for 25 percent of the worlds CO2 emissions, has refused to ratify the only international agreement to cut greenhouse gases, such as carbon dioxide, the Kyoto protocol, which came into force this year and commits industrialised nations to cut emissions to 5 percent below 1990 levels by 2012.

Even those countries which have ratified the Kyoto protocol appear unlikely to meet its modest goals, Dyson said. Between 1990 and 2002 Canadas CO2 emissions rose by 22 percent and Japan by 13 percent while those of the EU emissions have risen by 3.4 percent.

The worlds poor response so far to global warming was similar to that for other long-term threats such as HIV/AIDS with the early development of a scientific consensus followed by "avoidance, denial and recrimination" with little behavioural change, said Dyson.

Immigration to rich countries is also likely to a "significant role" in CO2 emissions growth.

The United States and Canada currently have the worlds highest average per capita CO2 emissions at 19.9 tons per year, 20 times more than for sub-Saharan Africa, and are expected to increase their population by 132 million during the next 50 years, due largely to immigration.

Economic development in poor countries will also increase emissions. Between 1990-99 emissions in North Africa and West Asia rose by 19.7 percent and South America 22.5 percent.

Population growth is also likely to put more people at greater risk from climate change.

"The continuing process of urbanisation will mean that extremely large numbers of people, probably several billion, will be living in low-lying, densely populated coastal areas of the developing world, and their situation is likely to be particularly exposed," Dyson told the conference.

"Flooding of coastal areas, which might result partly from sea level rise and partly from increase rainfall, could lead to the simultaneous loss of cropland and urban infrastructure, producing food price rises, large scale migration and possibly significant socio-political disruption," the professor said.

Before the industrial revolution in the 18th century, the CO2 level in the atmosphere was steady at around 280 parts per million.

When the Kyoto protocol was drawn up in 1997, the CO2 level had reached at 368 parts per million (ppm). In 2004, it hit 379 ppm.

Most predictions of increasing temperatures, floods, droughts, storms and rising sea levels are based on a concentration of 550 ppm. On current trends, this figure, is likely to be reached in the second half of this century.

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