Scientists and representatives of world governments have agreed a report warning that climate change could have "abrupt" and "irreversible" consequences, writes Jamie Smythin Valencia.
The report, which has been prepared by the 130-state Intergovernmental Panel on Climate Change (IPCC), is expected to play a critical role in persuading governments to sign up to a new global agreement to curb greenhouse gas emissions.
It will be presented to environment ministers in two weeks at a UN conference in Bali, Indonesia, where talks on creating a successor to the Kyoto Protocol are expected to begin.
UN secretary general Ban Ki- moon will launch the IPCC report today, following five days of tough political negotiations between delegations in Valencia, Spain.
IPCC delegates agreed yesterday on the key 20-page summary for policy-makers, which outlines the latest scientific knowledge on the causes and effects of climate change.
Last night the IPCC delegates were close to agreeing a related technical report on climate change.
The summary for policy-makers paints a stark picture of how climate change is already negatively affecting vulnerable habitats and communities.
It warns of extreme consequences unless drastic action is taken soon to curb greenhouse gas emissions.
This report, which amalgamates the science from three existing reports on climate change published this year by the IPCC, concludes that evidence of climate change is now "unequivocal" and human activities since 1750 have contributed to the warming.
It says there is new and stronger evidence of the observed impacts of climate change on vulnerable systems such as polar and high mountain communities and ecosystems.
The risks of extreme weather, such as drought, heatwaves and tropical cyclones, are projected with more confidence than in previous IPCC reports.
If no effort is made to mitigate climate change by curbing CO2 emissions, the report warns that in the long term it could exceed the capacity of "natural, managed and human systems to adapt".
It also warns that the level of emissions-reduction required to bring about a stabilisation in the warming of the earth may have been underestimated.
To limit global warming to 2 to 2.4 degrees above pre-industrial levels, CO2 emissions would need to peak within less than 10 years, and global CO2 emissions have to be reduced by 50 to 85 per cent relative to 2000, according to the report.
It also concludes that even under the most stringent scenarios for cutting CO2 emissions, further warming and some associated impacts are already unavoidable.
Stephan Singer, a climate and energy expert at the Worldwide Fund for Nature, said agreement on the summary report meant no governments could shy away from the dire consequences of climate change and now must act to cut emissions.
"If this is not enough to persuade policy-makers of the need to sign up to a new mechanism to cut greenhouse gas emissions, then I don't know what is," he said.
Delegates said the debate over the summary report was long and tough, with representatives of big oil-producing states such as the US and Saudi Arabia subjecting every line to scrutiny.