The cuts in greenhouse gases offered at the 192-nation climate conference are "clearly not enough" to assure the world it will head off dangerous global warming, a key U.N.-affiliated scientist said Saturday.
Such projections, moreover, don't even account for the "potentially hugely important" threat of methane from the Arctic's thawing permafrost, other researchers said.
Midway through the two-week U.N. conference, richer nations are offering firm reductions in emissions of carbon dioxide and other greenhouse gases ranging from 3-4 percent for the U.S. to 20 percent for the European Union, in terms of 2020 emission levels compared with 1990.
One authoritative independent analysis finds the aggregate cuts amount to 8-12 percent. But the Intergovernmental Panel on Climate Changes (IPCC), the U.N.-sponsored science network, recommends that reductions average in the 25-40-percent range to keep global temperature increases below 2 degrees C (3.6 F) above preindustrial levels and head off the worst of global warming.
"I think it is clearly not enough," the IPCC's Thomas Stocker said of the numbers discussed here. "We are by far short of having security that the 2-degree target will be met."
The Swiss physicist heads the IPCC's Working Group I, the climate science group that, among other things, assesses the impact that emissions _ from fossil-fuel burning, deforestation and other sources _ have on concentrations of global-warming gases in the atmosphere and then on temperatures.
Stocker told reporters the IPCC-recommended target "may be too much to ask at this stage" _ too politically daunting to achieve in the current annual conference. But he suggested climate talks should aim at longer-term commitments, over decades, not the short commitment periods envisioned in the annual conferences.
Even limiting the temperature rise to 2 degrees C would not forestall serious damage, the IPCC chairman, Rajendra Pachauri, told reporters. "We would get sea-level rise, through thermal expansion alone, of 0.4 to 1.4 meters" (1.3 feet to 4.5 feet), he said.
Climate science co-chair Stocker acknowledged that IPCC projections do not include the potential "tipping point" addition of trapped methane, a powerful greenhouse gas that would be released as permafrost thaws in the far north.
Plant and animal matter entombed in that frozen Arctic soil for millennia would decompose as it thaws, attacked by microbes, producing carbon dioxide and _ if in water _ methane, many times more powerful than CO2 in warming the atmosphere. Other methane would be released as the oceans warm deposits of methane hydrates, ice-like formations deep underground and under the seabed in which methane molecules are trapped in crystals of frozen water.
"It is potentially hugely important," Richard Betts of the Met Office Hadley Center, Britain's climate science center, said of the latent methane in another news briefing. "The size of the reserves are not fully known and are not captured fully in our models" _ the supercomputer simulations used to project climate change.
Russian researchers in Siberia, in particular, have expressed alarm about methane's potential, warning of a possible surge in emissions in the north, where Earth is warming most, adding several degrees to global temperatures and causing unpredictable consequences for the climate. Others say massive seeps of methane might take centuries.
"We don't really know enough yet about methane feedback," Hadley Center climatologist Vicki Pope told reporters.
The British institution says intensive research on Arctic methane may allow it to be included in Hadley climate predictions within five years. Last year six U.S. national laboratories launched a joint investigation of rapid methane release, and last July the IPCC chairman, Rajendra Pachauri, asked his scientific network to focus on "abrupt, irreversible climate change" from thawing permafrost. The IPCC's next periodic assessment report is due in 2013.
We're "walking toward a cliff in the dark," Betts said of such unknowns in climate. "It's out there somewhere, you don't know where, and so it makes sense to stop."