Carbon dioxide is accumulating in the atmosphere much faster than scientists expected, raising fears that humankind may have less time to tackle climate change than previously thought.
New figures from dozens of measuring stations across the world reveal that concentrations of CO2, the main greenhouse gas, rose at record levels during 2006 - the fourth year in the last five to show a sharp increase. Experts are puzzled because the spike, which follows decades of more modest annual rises, does not appear to match the pattern of steady increases in human emissions.
At its most far reaching, the finding could indicate that global temperatures are making forests, soils and oceans less able to absorb carbon dioxide - a shift that would make it harder to tackle global warming. Such a shift would worsen even the gloomy predictions of the Stern Review which warned that we had little over a decade to tackle rising emissions to avoid the worst effects of climate change.
David Hofmann of the US National Oceanic and Atmospheric Administration (Noaa), which published the figures, said: "Over this last decade the growth rates in carbon dioxide have been higher. I don't think we can plausibly say what's causing it. It's something we're going to look at."
Peter Cox, a climate change expert at Exeter University, said: " The concern is that climate change itself will affect the ability of the land to absorb our emissions." At the moment around half of human carbon emissions are reabsorbed by nature but the fear among scientists is that increasing temperatures will work to reduce this effect.
Professor Cox added: "It means our emissions would have a progressively bigger impact on climate change because more of them will remain in the air. It accelerates the rate of change, so we get it sooner and we get it harder."
Carbon dioxide concentration in the atmosphere is measured in parts per million (ppm). From 1970 to 2000 that concentration rose by about 1.5ppm each year, as human activities sent more of the gas into the atmosphere. But according to the latest figures, last year saw a rise of 2.6ppm. And 2006 was not alone. A series of similar jumps in recent years means the carbon dioxide level has risen by an average 2.2ppm each year since 2001.
Above-average annual rises in carbon dioxide levels have been explained by natural events such as the El Niño weather pattern, centred on the Pacific Ocean. But the last El Niño was in 1998, when it resulted in a record annual increase in carbon dioxide of 2.9ppm. If the current trend continues, this year's predicted El Niño could see the annual rise in carbon dioxide pass the 3ppm level for the first time.
Prof Cox said that an increase in forest fires, heatwaves across Europe and the Amazon drought of 2005 could have helped to drive up carbon dioxide levels. Such events are predicted to become more frequent with rising global temperatures. He admitted "the jury is still out" on whether the recent spike is evidence of a significant change, although some computer models predict that the Earth will start to absorb less carbon dioxide some time this decade.
"Over the past few years carbon dioxide has been going up faster than we would expect, based on the rate that emissions are increasing," Prof Cox said.
The BBC reports Arctic sea ice 'faces rapid melt':
A new model forecasts largely ice-free summers by 2040
The Arctic may be close to a tipping point that sees all-year-round ice disappear very rapidly in the next few decades, US scientists have warned.
The latest data presented at the American Geophysical Union Fall Meeting suggests the ice is no longer showing a robust recovery from the summer melt.
Last month, the sea that was frozen covered an area that was two million sq km less than the historical average.
"That's an area the size of Alaska," said leading ice expert Mark Serreze.
"We're no longer recovering well in autumn anymore. The ice pack may now be starting to get preconditioned, perhaps to show very rapid losses in the near future," the University of Colorado researcher added.
The sea ice reached its minimum extent this year on 14 September, making 2006 the fourth lowest on record in 29 years of satellite record-keeping and just shy of the all time minimum of 2005.
Dr Serreze's concern was underlined by new computer modelling which concludes that the Arctic may be free of all summer ice by as early as 2040.
The new study, by a team of scientists from the National Center for Atmospheric Research (NCAR), the University of Washington, and McGill University, found that the ice system could be being weakened to such a degree by global warming that it soon accelerates its own decline.
"As the ice retreats, the ocean transports more heat to the Arctic and the open water absorbs more sunlight, further accelerating the rate of warming and leading to the loss of more ice," explained Dr Marika Holland.
"This is a positive feedback loop with dramatic implications for the entire Arctic region."
Eventually, she said, the system would be "kicked over the edge", probably not even by a dramatic event but by one year slighter warmer than normal. Very rapid retreat would then follow.
Sooner or later
In one of the model's simulations, the September ice was seen to shrink from about 5.9 million sq km (2.3 million sq miles) to 1.9 million sq km (770,000 square miles) in just a 10-year period.
By 2040, only a small amount of perennial sea ice remained along the north coasts of Greenland and Canada, while most of the Arctic basin was ice-free in September.
"We don't think that state has existed for hundreds of thousands of years; this is a dramatic change to the Arctic climate system," Dr Holland told the BBC.
Dr Serreze, who is not a modeller and deals with observational data, feels the tipping point could be very close.
"My gut feeling is that it might be around the year 2030 that we really see a rapid decline of that ice. Now could it occur sooner? It might well. Could it occur later? It might well.
"It depends on the aspects of natural variability in the system. We have to remember under greenhouse warming, natural variability has always been part of the picture and it always will be part of the picture."
The average sea ice extent for the entire month of September this year was 5.9 million sq km (2.3 million sq miles). Including 2006, the September rate of sea ice decline is now approximately -8.59% per decade, or 60,421 sq km (23,328 sq miles) per year.
At that rate, without the acceleration seen in the new modelling, the Arctic Ocean would have no ice in September by the year 2060.
Gaia Scientist Lovelock Predicts Planetary Wipeout:
The earth has a fever that could boost temperatures by 8 degrees Celsius making large parts of the surface uninhabitable and threatening billions of peoples' lives, a controversial climate scientist said on Tuesday.
James Lovelock, who angered climate scientists with his Gaia theory of a living planet and then alienated environmentalists by backing nuclear power, said a traumatized earth might only be able to support less than a tenth of it's 6 billion people.
"We are not all doomed. An awful lot of people will die, but I don't see the species dying out," he told a news conference. "A hot earth couldn't support much over 500 million."
"Almost all of the systems that have been looked at are in positive feedback ... and soon those effects will be larger than any of the effects of carbon dioxide emissions from industry and so on around the world," he added.
Scientists say that global warming due to carbon emissions from burning fossil fuels for power and transport could boost average temperatures by up to 6C by the end of the century causing floods, famines and violent storms.
But they also say that tough action now to cut carbon emissions could stop atmospheric concentrations of CO2 hitting 450 parts per million -- equivalent to a temperature rise of 2C from pre-industrial levels -- and save the planet.
Lovelock said temperature rises of up to 8C were already built in and while efforts to curb it were morally commendable, they were wasted.
"It is a bit like if your kidneys fail you can go on dialysis -- and who would refuse dialysis if death is the alternative. We should think of it in that context," he said.
"But remember that all they are doing is buying us time, no more. The problems go on," he added.
Lovelock adopted the name Gaia, the Greek mother earth goddess, in the 1960s to apply to his then revolutionary theory that the earth functions as a single, self-sustaining organism. His theory is now widely accepted.
In London to give a lecture on the environment to the Institution of Chemical Engineers, he said the planet had survived dramatic climate change at least seven times.
"In the change from the last Ice Age to now we lost land equivalent to the continent of Africa beneath the sea," he said. "We are facing things just as bad or worse than that during this century."
"There are refuges, plenty of them. 55 million years ago ... life moved up to the Arctic, stayed there during the course of it and then moved back again as things improved. I fear that this is what we may have to do," he added.
Lovelock said the United States, which has rejected the Kyoto Protocol on cutting carbon emissions, wrongly believed there was a technological solution, while booming economies China and India were out of control.
China is building a coal-fired power station a week to feed rampant demand, and India's economy is likewise surging.
If either suddenly decided to stop their carbon-fuelled development to lift their billions of people out of poverty they would face a revolution, yet if they continued, rising CO2 and temperatures would kill off plants and produce famine, he said.
"If climate change goes on course ... I can't see China being able to produce enough food by the middle of the century to support its people. They will have to move somewhere and Siberia is empty and it will be warmer then," he said.