by Stephen Leahy
The prospect of a four-degree Celsius rise in global average temperatures in 50 years is alarming – but not alarmist, climate scientists now believe. Eighteen months ago, no one dared imagine humanity pushingthe climate beyond an additional two degrees C of heating, but rising carbon emissions and inability to agree on cuts has meant science must now consider the previously unthinkable.
Four degrees of warming would be hotter than any time in the last 30 million years, and it could happen as soon as 2060 to 2070. "Four degrees C is definitely possible … This is the biggest challenge in our history," Chris West of the University of Oxford's UK Climate Impacts Programme told participants at the "4 Degrees and Beyond, International Climate Science Conference" at the University of Oxford last week.
It is a world with a one-to-two metre sea level rise by 2100, leaving hundreds of millions homeless. This will head to 12 metres in the coming centuries as the Greenland and Western Antarctic ice sheets melt, according to papers presented at the conference in Oxford.
Reality and the US Senate
"Political reality must be grounded in physical reality or it's completely useless," John Schellnhuber, director of the Potsdam Institute for Climate Impact Research, told the conference. Schellnhuber recently briefed US officials, but he says they chided him that his findings were "not grounded in political reality" and that "the [US] Senate will never agree to this." He had told them that the US must reduce its emissions from its current 20 tonnes of carbon per person average to zero tonnes per person by 2020 to have an even chance of stabilizing the climate around two degrees C. China's emissions must peak by 2020 and then go to zero by 2035, based on the current science, he added.
Even with a two-degree rise, most of the world's coral reefs will be lost, large portions of the ocean will become dead zones, mountain glaciers will largely vanish and many other ecosystems will be at risk, Schellnhuber warned. And there is the risk of reaching a tipping point where the warming rapidly accelerates. Continuing on the current high emissions path means average global temperatures would increase by 4.0 to 5.6 degrees by 2090, if not earlier. Brazil, much of Canada, parts of the US, Siberia and Central Europe would be eight degrees warmer than in the past 50 years. Computer models show the Arctic warming by 15 degrees while many other regions of the world would experience 10 degrees more warming.
These scenarios do not include potential tipping points like the release of the 1.5 trillion tonnes of carbon in northern permafrost or the melting of undersea methane hydrates.
Put your feet up and die
In a four-degree warmer world, adaptation means "put your feet up and die" for many people in the world, Oxford's Chris West said bluntly. One to two billion people will not have access to adequate fresh water because of the major shift in rainfall patterns, said Nigel Arnell, director of the Walker Institute for Climate Systems Research at the University of Reading in Britain.
Up to 15 percent of existing or potential cropland – and 40 percent in Africa – will become too dry and too hot for food production. While there might be some gains in northern areas like Canada and Russia, generally the soils there are not suitable for crops, he said.
Carbon emissions must stop
The current focus on CO2 concentrations like 450 parts per million (ppm) or 350 ppm is not the right approach since it is the total cumulative emissions that determine how warm the planet will get, said Myles Allen of the Climate Dynamics group at University of Oxford’s Atmospheric, Oceanic and Planetary Physics Department. If climate negotiators only look at slowing rates of carbon emissions, the total amount of carbon in the atmosphere will continue to increase. "We didn't save the ozone layer by rationing deodorants," said Allen.
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Stephen Leahy is an environmental journalist from Uxbridge Ontario.
[From WS November/December 2009]