UN secretary general Ban Ki-Moon has called on the US and China to play a more constructive role in combating climate change ahead of crucial talks on a new global climate treaty next month.
He also warned that changing weather and temperature patterns - which he described as the "defining challenge of our age" - threatened to push developing nations into a poverty trap unless there was a deal to curb CO2 emissions.
The secretary general's challenge to the world's two greatest greenhouse gas emitters came just two weeks before the world's environment ministers meet in Bali, Indonesia, to begin talks on creating a global climate treaty to replace the Kyoto Protocol, which expires in 2012.
Speaking at the launch of the final report of the UN Intergovernmental Panel on Climate Change (IPCC), prepared by representatives from 130 countries, Mr Ban said the stage was now set for a comprehensive climate change deal that all nations could embrace.
"I look forward to seeing the US and China playing a more constructive role, starting from the Bali conference . . . Both countries can lead in their own way," he told delegates from 130 states, who agreed the wording of a new report on climate change.
The US and China are signatories to Kyoto. However, the US has not ratified the treaty, and China, along with other developing countries, is not bound by its mandatory emissions caps.
The IPCC report, which will be presented to environment ministers in Bali, summarises the risks of global warming.
It concludes that evidence of warming is now "unequivocal" and warns of "abrupt" and "irreversible" consequences caused by climate change.
It is 90 per cent certain that human activity is causing warming and some impacts are unavoidable, even if immediate steps are taken to curb greenhouse gas emissions, says the report.
Reductions in greenhouse gases must start immediately to avert a global climate disaster that could leave island nations submerged and abandoned, reduce African crop yields by 50 per cent, and cause a 5 per cent decrease in global gross domestic product.
It also presents a wide variety of measures to mitigate climate change and says implementing these solutions would only reduce global economic growth marginally.
The IPCC says there has been an improvement in the understanding of climate change. This has enabled scientists to identify many of the risks associated with warming with a higher degree of confidence and to upgrade some of the risks identified in earlier reports.
The Irish Government will be among those represented at next month's summit. Yesterday, Minister for Communications, Energy and Natural Resources Eamon Ryan welcomed the report and said the Government was committed to meeting its targets on carbon emissions, energy efficiency and renewable energy.
"This report shows us so clearly that the time for debate on the science and the seriousness of climate change is over," he said.
"There is no reason why Ireland cannot lead the way internationally on this issue. We will need every political party, every department, local authority and citizen to become aware of the impact of their actions and choices. These impacts will be felt both in our own country and beyond the borders of the State."
The IPCC report warns that the risk of big increases in sea levels due to the melting of the Greenland and possibly Antarctic ice sheets may be larger than previously expected, and this could eventually result in sea levels increasing by several metres.