Recent research suggests that the scientific consensus within the UN-backed Intergovernmental Panel on Climate Change (IPCC) may have been too optimistic.
A group of researchers, most of whom are authors of previous IPCC reports, said last month that sea levels are set to rise much more quickly than expected.
The 'Copenhagen Diagnosis' sought to provide an update on the science of climate change in order to push international climate negotiators into decisive action. It showed that sea level has risen by over five centimetres in the past 15 years, exceeding previous IPCC projections by 80%.
The scientists warned that the world must prepare for sea levels to rise by over a metre by the end of this century and several metres over the following centuries. Both the Greenland and Antarctic ice sheets have started to lose mass, and the Arctic sea ice has melted far more quickly than expected, they stressed.
The scientists said global emissions would have to peak between 2015 and 2020 and decline rapidly afterwards in order to give the world a "reasonable chance" of avoiding the worst impacts of climate change.
Adding to the sense of emergency, the World Meteorological Organisation announced on 8 December that the year 2009 will likely rank among the ten warmest in the past 160 years of climate recording. The UN agency said the last decade had been warmer than that of the 2000s, which in turn was warmer than the 1980s.
Moreover, the economic argument for immediate action has been forcefully made by parties which favour reaching an ambitious agreement in Copenhagen.
The European Commission's Joint Research Centre (JRC) estimated last month that global warming could result in annual losses to EU GDP in the range of €20 to €65 billion.
The JRC's scenario presumes that temperatures will rise by between 2.5°C and 5.4°C by the 2080s, wreaking havoc on sensitive areas like agriculture, river flooding, coastal systems and tourism. However, the economic welfare of Europeans will still continue to improve, albeit more slowly, the researchers said.
Sceptics strike back
But climate sceptics have also been regrouping on the sidelines of the climate negotiations.
The credibility of the IPCC was called into question by leaked emails between top climate scientists in a scandal dubbed 'climategate' in the media. Hackers stole emails, some over ten years old, from the server of the University of East Anglia, which were then used as evidence that scientists had colluded to manipulate data to more dramatic effect in the IPCC reports.
Scientists said the accusations were no more than a smear campaign and insisted the emails contained nothing that would call into question global consensus on climate change.
Concerns were mounting, however, that the revelations could disrupt negotiations over a successor to the Kyoto Protocol, with less enthusiastic countries seizing upon them as a reason to wriggle out of making commitments. Saudi Arabia, for one, suggested that the incident would impact on what could be achieved in Copenhagen.
Indeed, a climate report released by the Indian environment minister last month questioned Western models of calculating global warming statistics in a quest to end reliance on Western science. It argued that there is no evidence that climate change is causing Himalayan glaciers to melt.
The IPCC said Himalayan glaciers are melting more quickly than those in other parts of the world. The Indian government's findings were dismissed as "schoolboy science" by the panel's chair, Rajendra Pachauri, according to news reports.
Researchers questioning global warming organised an alternative conference on the sidelines of the UN climate meeting in Copenhagen. Over 150 top scientists signed an open letter to the UN to request more data to justify the claim that humans are indeed causing climate change.
