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."

In other words, the world's present infrastructure—cars, power plants, steel mills and the like—already emits 80 percent of permissible greenhouse gas emissions, leaving essentially no room for growth after 2017. "After that point, we will have to build [an] all-zero carbon infrastructure," Cozzi notes thanks to known amounts of oil, coal and natural gas that, if burned, would produce much more CO2 than would be consistent with greenhouse gas concentration target of 450 parts per million.

The alternative is more expensive. The IEA's latest World Energy Outlook notes that for every dollar not spent on emissions reductions in the next decade, an additional $4 would need to be spent after 2020 to compensate.

The challenge, however, may be less about slow-to-change infrastructure  as about an expected lifestyle for Americans, Europeans, Japanese and, more recently, Chinese and Indians. "There is a lock-in effect in terms of habits and lifestyles," such as driving cars and wasting electricity, notes economist Leena Srivastava of The Energy and Resources Institute in New Delhi.  The resistance to changing a national lifestyle is perhaps best embodied by a statement from President George H.W. Bush back in 1992: "The American way of life is not up for negotiation."

In the U.S., change instead has focused on renewable sources of energy and improved efficiency, such as higher kilometers-per-gallon fuel standards for cars and trucks. "We're about 6 percent below 2005 levels right now," says U.S. climate-change envoy Todd Stern, and committed to reducing 17 percent from that level by 2020. Still, the U.S. remains the world's second largest emitter of greenhouse gases, after China.

Rising incomes around the world will make greenhouse reductions ever more challenging, and the latest data prove it: Developing countries such as China, India, Brazil and Indonesia now emit more in aggregate than developed countries, according to a study published December 4 in Nature Climate Change. "In the next 10 years, our energy consumption will definitely still increase," says Liu Qiang of the Energy Research Institute in Beijing. "That is our practical demand and a practical need," in China, particularly given the 128 million Chinese still living on $1 per day. Plus, for the growing Chinese middle class, "it is not so easy to change the lifestyle," Qiang notes. The goal in China is to increase the share of renewables and nuclear generation to 15 percent of primary energy in the next decade, which will still leave coal and oil—and their attendant greenhouse gas emissions—the lion's share.

Fortunately, improving access for the roughly two billion people without modern energy could also help slow the momentum of climate change by reducing deforestation (done to obtain fuel wood) and cutting emissions of soot from cooking fires. "We're all grappling with two defining challenges: overcoming inequality and climate change," observed economist Lord Nicholas Stern at the same event, dubbed "Momentum for Change" by the U.N. "If we fail on one, we fail on the other."