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."