THE world is on the cusp of a ''tipping point'' into dangerous climate change, scientists measuring methane leaking from the Arctic permafrost and a report to the United Nations have warned.
Independent lines of evidence now show that human greenhouse gas emissions are warming the Arctic and triggering the release of more methane, carbon dioxide and other gases.
''The permafrost carbon feedback is irreversible on human time scales,'' says the report, Policy Implications of Warming Permafrost. ''Overall, these observations indicate that large-scale thawing of permafrost may already have started.''
The report's researchers led by Kevin Schaefer, of the University of Colorado, summarised recent permafrost research and found that even if humans made deep cuts to their greenhouse gas emissions, the thaw would go on for centuries, increasing global warming. "Anthropogenic emissions targets in the climate change treaty need to account for these emissions or we risk overshooting the 2 degrees Celsius maximum warming target," Professor Schaefer said.
The findings are buttressed by other research in the air and on the ground in the Arctic.
A NASA expedition in Alaska is measuring the methane and carbon dioxide filtering out of the thawing permafrost as frozen organic matter warms up and begins to decay. ''We're finding very, very interesting changes, particularly in terms of methane concentrations,'' the expedition's principal investigator, Charles Miller, told Fairfax Media.
''We're seeing biological activity in various places in Alaska that's much more active than I would have expected, and also much more variable from place to place. There are changes as much as 10 to 12 parts per million for CO2 - so that's telling us that the local biology is doing something like five or six years' worth of change in the space of a few hundred metres.''
Researchers at the University of Alaska agreed it was now clear a massive thaw was under way.
The extra emissions are not accounted for in the Kyoto Protocol agreement that some nations, including Australia, are using as a guide for their greenhouse gas cuts.
''It's a significant problem in the carbon budget,'' said Pep Canadell, a CSIRO scientist and executive director of the Global Carbon Project. He calculated, using data in Professor Schaefer's report, that the extra greenhouse gases would cost an extra $35 billion to abate if they were valued under the federal government's $23-per-tonne carbon price.
UN Environment Program executive director Achim Steiner called on nations to cut fossil fuel emissions faster and start accounting for permafrost emissions.
"Permafrost is one of the keys to the planet's future because it contains large stores of frozen organic matter that, if thawed and released into the atmosphere, would amplify current global warming and propel us to a warmer world," he said.