Who would have thought the United States would one day be a leader in cutting greenhouse gas emissions?
This is the nation, after all, where a former chairman of the Senate committee on the environment, James Inhofe, wrote a book about global warming called “The Greatest Hoax.” This is where a presidential election took place not six months ago in which climate change barely merited a mention, buried under an avalanche of promises to dig for coal and drill for oil.
Fuel economy performance for cars and trucks is still among the worst in the developed world. And only 7 percent of the nation’s energy comes from renewable sources, less than in most other advanced nations.
Yet when President Obama talked about the nation’s energy revolution during his State of the Union address last month, he could have boasted that American emissions of CO2 had fallen almost 13 percent since 2007. It was perhaps the biggest decline among industrial countries, and substantially steeper than in Europe, which has been much more committed to combating climate change.
Carbon emissions from the United States have never fallen this much, not after the first oil price shock following the Arab oil embargo of 1973, nor after the Iranian revolution of 1979, when American drivers suddenly discovered the virtues of Japanese small cars and President Jimmy Carter installed solar panels on the White House to heat the water.
What stands out most in this shift, however, is not environmental regulation or public concern about global warming but the price of energy and market-driven technological advancements. “It wasn’t so much a policy shift that brought carbon emissions down,” said James Hamilton, an energy economist at the University of California, San Diego. “It was irresistible market forces.”
The United States consumes 9 percent less energy for each $1 of G.D.P. than it did five years ago. Total energy use has fallen about 5 percent in the last five years.
To be sure, regulations have contributed to the process; tighter fuel economy standards are expected to lead automakers to double the fuel efficiency of new cars and light trucks by 2025. Tax breaks are encouraging companies to invest in renewable energy sources and retrofit buildings to increase energy efficiency.
But the main reasons are economic. The great recession and the world’s sluggish recovery have depressed energy use. As in the 1970s, high oil prices have encouraged drivers to drive less, and switch to cars and trucks with better fuel economy.
There is a new force as well: high prices underpinned the widely trumpeted investment in hydraulic fracturing, or fracking, of shale rock rich in oil and natural gas, which pushed the price of gas to some $2 per thousand cubic feet last April, down from $9 four years ago. Cheap gas, in turn, has encouraged power companies to switch to the cleaner fuel, replacing the most heavily polluting source of energy that we know, coal.
Since 2007 the share of the nation’s electricity produced by gas-powered generators has jumped to 30 percent from 21 percent; CO2 emissions from electricity generation have tumbled more than 15 percent. This new fuel brings potential problems of its own. Environmental groups have sounded the alarm about chemicals and methane leaking from wells, potentially contaminating local water supplies and releasing additional carbon into the air.
But fracking also appears, against all odds, to have brought Mr. Obama’s early, hopeful promise to cut CO2 emissions by 17 percent between 2005 and 2020 within reach.
Will our carbon footprint continue to shrink? The Energy Department forecasts that CO2 emissions will tick up nearly 2 percent this year and 0.7 percent in 2014, as the economy recovers. Coal use in power plants is also expected to rebound as gas prices rise from their 2012 trough.
Historical precedent is not promising. The drive for energy efficiency that started in the 1970s did not continue once oil prices fell in the 1980s; among other things, American drivers fell in love with S.U.V.’s and trucks. In 1981, the Ford F-series pickup truck became the nation’s best-selling light vehicle. In 1986, Ronald Reagan had the White House solar panels taken down.
Nonetheless, there are some encouraging signs that this time may be different. The shift from coal to gas-fired power plants should be sped up by new rules requiring old coal generators to install expensive environmental equipment. Oil prices are supported by fast rising demand from the developing world and are unlikely to plunge despite new sources found in Canadian tar sands and American shale.
The United States’ experience with new fuels also offers some options for countries intent on pursuing economic growth while restraining carbon emissions.
China is rushing to develop its large fields of shale gas. Europe — where natural gas, most of it imported from Russia, is expensive and power plants rely heavily on coal — may follow suit. Several European governments have banned fracking or imposed sharp restrictions on it, but some — like Britain — are moving ahead.
Still, the United States’ serendipitous success in reducing greenhouse gas emissions suggests how much more needs to be done than switching from a particularly dirty source of carbon to a cleaner one.
Even if every American coal-fired power plant were to close, that would not make up for the coal-based generators being built in developing countries like India and China. “Since 2000, the growth in coal has been 10 times that of renewables,” said Daniel Yergin, chairman of IHS Cambridge Energy Research Associates.
Fatih Birol, chief economist of the International Energy Agency in Paris, points out that if civilization is to avoid catastrophic climate change, only about one third of the 3,000 gigatons of CO2 contained in the world’s known reserves of oil, gas and coal can be released into the atmosphere.
But the world economy does not work as if this were the case — not governments, nor businesses, nor consumers.
“In all my experience as an oil company manager, not a single oil company took into the picture the problem of CO2,” said Leonardo Maugeri, an energy expert at Harvard who until 2010 was head of strategy and development for Italy’s state-owned oil company, Eni. “They are all totally devoted to replacing the reserves they consume every year.”
Perhaps the most important lesson from the American natural gas boom is how prices drive both demand and supply. Putting a price on emissions of CO2 that reflects the burden they impose on the environment and the threat excessive amounts pose to future generations would almost certainly be the most effective strategy to persuade energy companies, power generators — and you and me — to spew less of it.