DURBAN, South Africa—By 2020, human activity could produce some 55 billion metric tons of greenhouse gases per year, up from roughly 36 billion metric tons currently. All the accumulating gas is enough to raise the global average temperatures by more than 3 degrees Celsius by century's end—more than triple the amount of warming that has already occurred. Emission reductions pledged under the 2010 Cancun Agreements, which cover some 85 percent of all national greenhouse gas emissions in the world, are meant to slow that warming. "I think its safe to say the current commitment is scientifically sound," argued Xie Zhenhua, vice chairman of China's National Development and Reform Commission and lead climate envoy, in a press briefing here on December 6.
Most climate scientists, however, would beg to differ. The latest science suggests that international negotiations are proceeding far too slowly to have any significant impact on global warming and may well dawdle too long to prevent catastrophic climate change. To meet the international target of restraining the warming of global average temperatures to just 2 degrees Celsius will require greenhouse gas emissions of just 44 billion metric tons in 2020. And even that amount might not be enough: James Hansen of NASA said this week at the American Geophysical Union meeting in San Francisco that the 2 degrees C target "is a prescription for disaster."
What's happening is that research keeps finding new trouble signs. Thanks to a rebound in global economic activity, 2010 saw the biggest single year increase in emissions ever—5.9 percent higher to be exact, according to the World Meteorological Organization. Another analysis, published December 4 in Nature Geoscience, found that nearly all of the nearly 1 degree C warming observed over the last century or so could be attributed to human emissions of greenhouse gases. (Scientific American is part of Nature Publishing Group.) The U.K. Met Office stated in a December 5 report that as many as 49 million people could be at risk from increased coastal flooding because of climate change, and along with many others from a drop in the production of staple food crops. The U.N. Intergovernmental Panel on Climate Change (IPCC) argues that emissions must be halved by mid-century to have any hope of restraining warming to 2 degrees C. "After four rounds of IPCC reports, is the science not clear enough?" asked Jato Sillah, Gambia's minister of forestry and environment during a speech on December 6.
"You can look at the science and see the trajectories, and it ought to inform what ought to be done. It might well cause us to say 'Gee, we need to do more'" to meet a 2-degree C target, says U.S. climate envoy Todd Stern.
In fact, if the world does nothing about greenhouse gas emissions and continues growing at the present rate, Earth could warm by as much as 6 degrees C, according to the International Energy Agency (IEA). Implementing the Cancun Agreements, negotiated at last year's climate meeting, would bring that temperature rise down to 3.5 degrees C. But to hit the 2-degree C target, the energy sector would need to decrease CO2 output after its peak in 2020, explains Laura Cozzi, principal analyst in the office of the chief economist of the IEA. "Oil demand and coal demand will have to go down from current levels."