Top climate scientists said Saturday that the eleventh-hour political deal hammered out at UN talks in Copenhagen falls perilously short of what is needed to stave off catastrophic global warming.
What many had hoped would be a planet-saving treaty locking major economies into strong commitments to shrink their carbon footprints came out as a three-page political accord with key numbers yet to be filled in.
"The easiest yardstick to evaluate is the two degree target," said Andrew Watson, a professor at the University of East Anglia in Britain.
"This agreement will almost certainly not be sufficient to enable that target to be met -- legally-binding tough limits in place over the next few years would be needed for that," he told AFP by email.
The Nobel-winning UN science panel warned in a benchmark 2007 report that if average temperatures increase by more than 2.0 degrees Celsius (3.6 degrees Fahrenheit) on pre-industrial levels, it could lead to runaway climate change and severe impact.
We have already travelled 0.7 C along that path.
More recent studies suggest the planet could hot up by a devastating 6.0 C (10.8 F), and that sea levels could rise by more than a metre (3.25 feet) by 2100 unless we slash CO2 concentrations in the Earth's atmosphere.
Such a hothouse scenario would create hundreds of millions of environmental refugees.
"Strictly speaking, it is a disappointment. We expected more," French climate scientist Herve Le Treut said of the new accord.
"What we have seen is the diverging interests of nation states and the planet."
Part of the problem is that most of the key mitigation targets have yet to be finalised.
"There is not much here to analyse. The accord doesn't have specific emissions targets for industrial countries, it doesn't have deviation from 'business as usual' goals for developing countries," said Alden Meyer of the Washington-based Union of Concerned Scientists.
"If you look at what is likely going to be listed in the annexes, you are going to be well over a 3.0 C," he told AFP. "The accord also fails to set a target for 'peak year' for global CO2 emissions, ideally around 2015.
"It is very critical that you get a peak and a decline starting soon," he added.
UN climate chief Yvo de Boer made much the same point in closing out the 13-day marathon meeting: "The opportunity to actually make it into the scientific window of opportunity is getting smaller and smaller."
The deal does contain a few silver linings, the scientists said.
"At least it may signal that there is some willingness to take action, so that we might have a hope of limiting the rise to 3.0 C - 4.0 C, and avoid the really unknown territory that lies beyond that," Watson said.
Le Treut agreed.
"It is too early to say it is a failure," he told AFP. "The scientific community had set the bar very high: halving global CO2 emissions by mid-century will be very tough."
That goal, embraced by rich nations, was dropped from early drafts of the accord due to objections from China and India, the world's number one and number three carbon emitters.
"From the evidence of the last two weeks, I would say we have a heck of a long way still to go if, as a species, we are to avoid the fate that usually afflicts populations that outgrow their resources," said Watson.
Explore further: NOAA establishes 'tipping points' for sea level rise related flooding