A week after publishing the starkest warning yet on the risks of climate change, UN experts meet in Berlin from tomorrow to assess options for limiting the threat.
A draft of the report suggests there is a 15-year window for feasible and affordable action to safely reach the UN-targeted global warming limit.
However, deep, swift curbs in carbon emissions will be needed, with a revolution in energy use, it says.
The report is the third chapter in the Fifth Assessment Report by the Intergovernmental Panel on Climate Change (IPCC).
Six years in the making, it provides policymakers with the latest science on global warming, to feed into national planning and the struggling effort to forge a worldwide pact by next year on curbing Earth-warming greenhouse gas emissions.
“I hope that this report will help to revitalize... climate politics and a sense of urgency from governments,” Bill Hare of the think tank Climate Analytics said.
The meeting comes eight days after the second volume of the report, on the likely impacts of climate change, was unveiled in Yokohama, Japan.
It issued unprecedented warnings that the risk of conflict, hunger, floods and mass displacement increased with every upward creep of the mercury.
The draft of the new 29-page summary, which will be hammered out in Berlin over five days before it is publicly released on Sunday next week, expresses no preferences for how to tame the problem, nor does it say what a safe level of warming would be.
However, it says the UN target — to limit average warming to 2oC over pre-industrial levels — remains feasible.
There is a “likely” chance of meeting it if greenhouse-gas concentrations by 2100 are between 430 and 480 particles per million (ppm) of carbon dioxide equivalent, according to the draft.
However, this meant “all countries” will have act quickly to mitigate, or ease, carbon emissions.
“Delaying mitigation through 2030 will increase the challenges,” the document says.
In raw terms, global carbon emissions of 49 billion tonnes of carbon dioxide equivalent in 2010 will have to be pegged to between 30 billion and 50 billion tonnes in 2030.
Emissions have maintained an upward curve, despite a small dip after the 2007-2008 global economic crisis, and will be hard to contain as developing economies consume ever more fossil fuel and the global population expands.
Greenhouse-gas levels are on track to bust 450ppm carbon dioxide equivalent by 2030 and reach between 750ppm and 1,300ppm carbon dioxide equivalent by 2100 if nothing is done, the document says.
The summary points to a wide range of policy options, but says that the most successful scenarios assume a stable, global carbon price.
Mitigation options include capturing and storing fossil-fuel emissions, switching to low-carbon alternatives, halting the thinning of carbon-capturing forests and boosting low-emission public transport schemes.
The draft turns the spotlight on energy — the need for low-carbon sources and ending waste.
Energy production emitted 14.4 billion tonnes of carbon dioxide, the chief greenhouse gas, in 2010. That figure could double or even triple by 2050, according to the report.
On the consumption side, buildings spewed 8.8 billion tonnes in 2010 and industry 13 billion — both figures set to increase by 50-150 percent by mid-century. Transport’s 6.7 billion tonnes of carbon dioxide could double over the same period.