Although natural gas burns more cleanly than coal, a new study argues that replacing all the world's coal power plants with natural gas would do little to slow global warming this century.
"There are lots of reasons to like natural gas, but climate change isn't one of them," said physicist Nathan Myhrvold, lead author of the new study. "It's worthless for [fighting] climate change, as far as we can tell."
The reason for that grim assessment: The carbon dioxide burden already is so large, and its lifetime in the atmosphere is so long, that even a switch to completely carbon-free electricity couldn't stop temperatures from rising over the next 100 years. Switching from coal to natural gas would cut the warming effect in 100 years' time by only about 20 percent, while switching to renewable or nuclear energy would slash the warming effect about two-thirds to three-quarters.
With this new study, Myhrvold has set out in a new direction. The former chief technology officer of Microsoft and founder of Microsoft Research, Myhrvold has also studied cosmology with Steven Hawking and published scientific studies on dinosaurs—including one on fossilized vomit. These days Myhrvold runs a company called Intellectual Ventures, and recently co-authored Modernist Cuisine, a six-volume tome on the science of cooking.
Myhrvold has long been interested in climate change, and for the new study he teamed up with climate researcher Ken Caldeira of the Carnegie Institution for Science in Stanford, California, to compare a variety of alternatives to coal-fired power plants.
The two scientists were wondering what effect it would have on the climate if the world were to switch from coal to any of a menu of other options. "We realized nobody had done it"—at least not in a systematic way, Myhrvold said. "I decided to take it to the lunatic extreme and try to do it myself."
Turning the Switch
The world currently has enough coal-fired power plants to produce about one terawatt of electricity—the equivalent to each of the seven billion people on Earth using two 75-watt light bulbs at the same time.
In their study published in February in Environmental Research Letters, Myhrvold and Caldeira looked at switching from one terawatt of coal power plants to natural gas-or to solar panels, or wind, or nuclear, or other options. And they tested the effects of making the whole transition in one year—a pace Myhrvold called "insane"—or over as long as a "leisurely" 100-year span.
"We found some really counterintuitive results," Myhrvold said.
Compared to emissions from coal, "cutting emissions by a factor of two or three hardly makes a difference," he said. To avoid a significant amount of warming this century, he added, "you must cut emissions by a dramatic factor"—by ten or twenty times.
If over the course of 40 years the world switched all the coal power plants over to natural gas, generating half as much greenhouse gas per watt-hour of electricity, then the warming would slow—but only by a small fraction. In the natural gas scenario, the study calculated a range of warming trajectories for warming 100 years from now, with temperatures 17 to 25 percent lower than they would be if the world stuck with coal.
But the cut in the warming trajectory was far sharper for a switch to energy sources with near-zero emissions—such as nuclear, wind, or solar energy. The reduction in the temperature increase was 57 to 81 percent, according to the study models.
In reality, the world faces an even more daunting challenge than that outlined in the study, which assumed that future electricity use would stay at today's levels. Almost universally, projections call for the world's electricity demand to increase in the next century.
"It's got to be a little depressing," Myhrvold admitted. But, he added, "It's really important from a policy perspective to understand what the dimensions of the problem are."
The results surprised even Caldeira, who specializes in climate change, and has studied how carbon dioxide from fossil fuels will likely linger in the atmosphere for a very long time—about a quarter of it remaining aloft for more than a thousand years.
This was "kind of obvious when you think about it, but I hadn't realized," Caldeira said.
Caldeira sees the results as "a Rorschach test," which he expects people will read in one of two ways. "You can say we need to go for the lowest emissions, and do it now," he said, "or you may throw your hands up in despair."
Defending the Bridge
Ads touting natural gas as a clean fuel appear regularly on TV. The American Clean Skies Foundation, one of the strongest advocates of natural gas, was founded by Aubrey McClendon, chief executive of Chesapeake Energy, the second-largest natural gas producer in the United States.
Patrick Bean, an energy policy adviser at the American Clean Skies Foundation, did not find fault with the study's results, but argued that natural gas could be helpful nonetheless.
The study looked at various replacements for coal one-by-one, but "we really need to rely on a mix" of different electricity sources, Bean said, arguing that wind and solar energy are still too expensive.
Given the "constraints of money and politics," natural gas still has an important role as a "bridge fuel" on the way to cleaner energy sources, including wind and solar, Bean said.
But Caldeira argued that if we invest more in natural gas in the near term, "it puts new investment money in the fossil fuel industry and expands the size of [its] political force."
Whatever our sources of energy, though, "conservation and efficiency are essential," Caldeira said. "It's clear that the problem becomes much more difficult if you're using energy wastefully."
This story is part of a special series that explores energy issues. For more, visit The Great Energy Challenge.