'We won't let sceptics hijack climate talks'

It has been billed as the most important meeting for half a century, and yesterday, with 15,000 people in attendance, the Copenhagen Climate Conference opened with a robust and angry defence of the science of global warming by two of the world's leading climate science figures.

Dr Rajendra Pachauri, the Nobel-Prize winning head of the UN's Intergovernmental Panel On Climate Change (IPCC), and Dr Jonathan Pershing, the head of the US delegation to the conference, both hit out at the theft of emails from the Climatic Research Unit of the University of East Anglia, which has been used by climate sceptics in Britain, the US and elsewhere to allege that global warming is not man-made.

There has been widespread speculation that the timing of the theft represented a specific attempt to destabilise the conference, in which the world community will attempt to construct a new treaty to cut back on the emissions of carbon dioxide causing the atmosphere to warm.

But yesterday Dr Pershing said that all the incident had done was to "release a barrage of further information which makes clear the robustness of the science." He said it was "shameful" how some of the scientists involved were now being pilloried.

Dr Pachauri told the conference opening ceremony, presided over by the Danish Prime Minister, Lars Lokke Rasmussen, that some people clearly found it "inconvenient" to accept the inevitability of the changes that would have to be made in the face of the climate change threat.

"The recent incident of stealing the emails of scientists at the University of East Anglia shows that some would go to the extent of carrying out illegal acts perhaps in an attempt to discredit the IPCC," he said. "But the panel has a record of transparent and objective assessment stretching back over 21 years, performed by tens of thousands of dedicated scientists from all corners of the globe."

The conference, being held at the giant Bella Centre in Copenhagen's southern suburbs, is bringing together 192 countries, all of whom accept the verdict of the IPCC's most recent report, published in 2007, that the warming of the climate system is "unequivocal" and that there is a better than nine out of 10 chance that it is being caused by human actions – principally the emissions of carbon dioxide from industry, transport and deforestation, which retain the Sun's heat in the atmosphere.

The 2007 report said that if CO2 emissions continued without being checked, the Earth's temperature would be likely to rise by between 1.8C and 4C over the coming century – with an outside chance that it could hit 6C, which would be disastrous for the natural world and human society. But more recent scientific assessments have suggested that emissions are now rising so fast that the Earth is firmly on track to hit the 6C rise if action is not taken.

Dr Pachauri listed for the conference – and for the world – some of the consequences global warming would lead to if it were left unchecked. They included widespread increases in droughts and floods, greater stress on water resources, increases in tropical cyclone intensity, more extinctions of wild species and the eventual melting of the Greenland ice sheet, which would cause sea levels around the world to rise by more than 20 feet.

Cutting back on the emissions responsible was now the urgent task of the "historically important meeting", he said. But it will not be a matter just for the thousands of delegates. Mr Rasmussen announced that the number of world leaders who would be attending the finale of the conference at the end of next week had now reached 110. He said: "Their presence reflects an unprecedented mobilisation of political determination to combat climate change. It represents a huge opportunity – an opportunity the world cannot afford to miss."

This morning the negotiations proper get under way, with the aim being an agreement in which the industrialised countries such as the US and Britain make strong commitments to cut back their CO2 by up to 40 per cent by 2020, with the leading developing countries such as China and India making firm pledges to move away from "business as usual" in terms of their emissions growth.

Underpinning the deal will have to be a major new financial agreement which provides the developing nations with billions of dollars from the rich world in new climate aid, to help them cut their emissions and also adapt to climate change which is now probably unavoidable, such as widely increased flooding.

Day One: The highlights

*UN Climate Conference, two years in preparation, opens in Copenhagen with 15,000 delegates, observers and media personnel in attendance.

*United Nations climate chief and head of American delegation attack climate sceptics and defend science behind global warming.

*110 heads of state and government, including US President Barack Obama, now preparing to attend conference finale next week.

*European Union says it wants stronger commitments from the US and China to cut CO2 before raising its own ambitions.

*South Africa is final big developing country to announce a climate target.

*Danish Prime Minister apologises to delegates for lack of Little Mermaid figurine in their conference kits.