Professor Katharine Richardson, who chaired the scientific steering committee for the conference, said it was now almost impossible for the world to achieve the UN target of preventing global temperature rise exceeding 2C.
"We can forget about the 2C"," said Richardson in an interview. "We are now facing the situation where we have to avoid a 5-6C rise in temperature."
Richardson said her comments were based on sifting through hundreds of science research papers submitted to the congress. Details of the research are being presented to delegates this week and will be used in a report for the UN.
Her comments were not the only bad news to emerge on the first day of the International Scientific Congress on Climate Change (IPCC) in Copenhagen. Other researchers warned that sea levels are now rising 50% faster than suggested by the Intergovernmental Panel on Climate Change in its 2007 report.
Comment: The ISCCC 'International Scientific Congress on Climate Change' or Climate Change Congress in Copenhagen is not the IPCC. It is not backed or supported by the IPCC and is in fact a political gathering backed by a group of 10 Universities designed to specifically promote the cause of Anthropogenic Global Warming in the most extreme fear mongering way possible. That these journalists and the Times UK would slip that subliminal in that it is the (IPCC) is just downright devious and shows their hand in the fear mongering propaganda.
It means the world's oceans could rise by a metre or more over the next century and that low-lying coastal areas will be at risk of inundation with hundreds of millions of people displaced, especially in developing countries.
Some of those attending the Copenhagen meeting have dubbed it "the end of the world conference" because the latest research emerging on climate change is so alarming.
"There is not a lot, if any, good news," said Richardson of the emerging science. "What we know now is that we are we facing the worst case scenario."
The warnings on temperature rise are linked to the surge in greenhouse gas emissions over the last decade. Currently humanity generates the equivalent of about 50 billion tonnes of CO2 a year through burning fossil fuels, agriculture, deforestation and other processes.
In its last report the IPCC made over-cautious assumptions about how these emissions would rise in future - and concluded it would be possible to prevent a total global temperature rise of more than 2C compared with pre-industrial times.
It has since emerged that these assumptions were misplaced and that emissions have grown at around 3 % a year - about twice as fast as the IPCC's worst case scenario.
Dr R K Pachauri, chairman of the IPCC, who won a 2008 Nobel prize for his work on climate, said temperatures had already risen by about 0.7C, compared with pre-industrial times and would probably rise by a further 1.8 - 4C over the next century.
This would give a total potential temperature rise of 2.5C - 4.7C. There was even an outside chance of much greater warming, of around 7C, he said.
He said: "There is no room now to argue that the earth is warming. Sadly policy makers have shied away from such findings and that is why there is no concensus on where to stabilise global temperatures or how," he said. Even a minimal temperature change of 1C would put food security and water availability at risk."
Other scientists were equally gloomy on the impacts of rising sea level, warning that rising oceans would have major impacts around the world and were likely to hit low-lying countries, particularly hard. Countries like Bangladesh, China, the Mumbai region of India were especially at risk but even developed ones like Britain would be affected badly.
Dr John Church of the Centre for Australian Weather and Climate Research, Hobart, Tasmania, Australia, told the conference, sea level rise by 2100 could be in the range of about one meter, or possibly more.
The warning comes from new research into the behaviour of glaciers and ice sheets, especially in Greenland. It had been thought the main effect of global warming was simply to melt them.
However, the new research shows that as water melts it sinks down to the bedrock under the glaciers and lubricates them, so that their movement to the sea accelerates sharply.
This has turned out to be a much more powerful effect than simple melting and means the IPCC, whose 2007 report projected a sea level rise of 18 - 59 cm by 2100, must once again revise its earlier findings.
Eric Rignot, Professor of Earth System Science at the University of California Irvine and Senior Research Scientist at NASA's Jet Propulsion Laboratory said the finding had emerged from research conducted after the IPCC report was written.
He said: "As a result of the acceleration of outlet glaciers over large regions, the ice sheets in Greenland and Antarctica are already contributing more and faster to sea level rise than anticipated. If this trend continues, we are likely to witness sea level rise one meter or more by year 2100."
The point of the Copenhagen meeting is to draw together all the latest science on climate change in preparation for the UN negotiations planned for this December at which politicians will try to draw up a replacement for the Kyoto treaty on reducing greenhouse gases, which expires in 2012.
However, John Ashton, a senior civil servant at the British Foreign Office, launched a startling attack - for a government official - on the ability of politicians to deal with climate change, or even understand it.
He said he believed politicians had still failed to grasp the seriousness of climate change - or were even prepared to bend scientific findings to purely political ends.
"Policymaking is not adapted to deal with the problem of climate change, " said Ashton. "Politiicans often see science as just another group and that opinions based on science are just another lobby. There are also plenty of people who due to ignorance or mischief are willing to confuse the issue."
Ashton did not name any particular politicians or issues but his comments come just weeks after the government gave its approval to the building of a third runway at Heathrow airport, an issue which is said to have left many of Britain's climate policy-makers seething.