Climate change could soon reach a major tipping point, say scientists who have revealed the death of billions of trees in the Amazon rainforest.
The dense rainforests of the Amazon are a vital defence against global warming, absorbing more than a quarter of the world's atmospheric CO2. But after the mass tree deaths, resulting from a record drought in the region during 2010, it's feared that the vast forest will begin to produce more CO2 than it can soak up.
If, as the new research warns, the Amazon turns from a carbon "sink" to a carbon "source", the change could trigger further tree deaths, resulting in a feedback loop that accelerates global warming.
"Put starkly, current emissions pathways risk playing Russian roulette with the world's largest forest," said tropical forest expert Simon Lewis of the University of Leeds, and who led the research published today in the journal Science.
Lewis is careful to point out that the 2010 drought - as well as an earlier one in 2005 which at the time was thought to be a once-in-a-century event - may still be explained by natural variations in climate.
But even given that uncertainty, Lewis is adamant that the one thing governments can't do is nothing.
"We can't just wait and see because there is no going back," Lewis told the UK's Guardian newspaper. "We won't know we have passed the point where the Amazon turns from a sink to a source until afterwards, when it will be too late."
Lewis's team used satellite imagery to measure rainfall in the region, and discovered that 2010's water shortage was even more severe than the drought of 2005, affecting a 60 per cent larger area and with a harsher dry season.
The research highlighting the extent of tree deaths will come as a serious blow to Brazilian authorities, who have themselves made extensive use of satellite imaging to clamp down on illegal logging, drastically reducing deforestation rates.
Today's paper in Science comes a day after environmental campaign group Greenpeace urged Facebook to sign a pledge that it will move towards greener sources of energy to power its massive data farms.
Currently, the social networking giant's infrastructure guzzles energy from CO2-emitting coal-fired power stations like there's no tomorrow.
Unless something changes, there may not be.