Climate experts sparred today over the wording of a UN report spelling out the grim impact of global warming and are struggling to meet tomorrow's deadline.
Delegates from more than 100 countries convened in Brussels this week to discuss the report and have yet to agree on all its contents, less than 24 hours before its scheduled release, people familiar with the talks said.
Hans Verolme, director of WWF global climate change programme
Two months ago, the United Nations Intergovernmental Panel on Climate Change (IPCC) predicted a three-degree average global temperature rise by the end of the century, with devastating fallout from melting ice caps and rising sea levels, heatwaves and droughts.
It predicts rising temperatures will lead to more hunger in Africa, the melting of Himalayan glaciers, more heatwaves in the United States and damage to Australia's Great Barrier Reef.
"There is wrangling happening," said Hans Verolme, director of the global climate change programme at WWF, an environmental group that is an observer to the meeting. "There are some who are questioning the scientific basis ... of some of the summary statements, which is leading the authors to have to go back to the underlying document."
The UN panel's report is the most authoritative study since 2001 on the regional impact of climate change. Mr Verolme said the fact world leaders would read the report's summary had added pressure for consensus on the wording.
"There is discussion whether something is 'likely' or 'very likely', and my sense is that is because people are aware here that heads of state are paying attention," he said. "If the text says this is very likely, the response (from governments) has to be very significant."
The IPCC, which draws together 2,500 scientists from more than 130 countries, also said it was now more than 90 per cent certain that human behaviour is to blame for the crisis.
This week 50 IPCC scientists are finalising a follow-up report to be published today, setting out how the worst-case scenario could hit ordinary people. They are expected to conclude that the poorest nations will be hardest hit because they are most vulnerable and least able to adapt.
The UN scientists are likely to end their four-day meeting with more stark warnings that hundreds of millions of people are vulnerable to flooding due to rising sea levels.
Especially at risk are those in densely populated, low-lying areas of the world already exposed to tropical storms and other threats that are increasingly linked to climate change.