If you're accustomed to thinking of greenhouse gas emissions being spewed by coal-burning power plants as the major culprit in climate change, you're in for a surprise. A new analysis of federal government data by a University of Michigan researcher indicates that smokestacks are about to be surpassed by tailpipes as the biggest U.S. source of the human-generated pollution that's driving global warming.
John M. DeCicco, a research professor at the University of Michigan Energy Institute, writes in his Cars and Climate blog that when it comes to carbon dioxide emissions, power plants have topped motor vehicles, aircraft and other forms of transportation for the past four decades.
But over seven of past eight months, transportation has been a greater source of carbon pollution, and 2016 is on track to be the first year in which it overtakes electrical power generation as the chief source of carbon pollution.
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The shift completes the reversal of a trend that started in the early 1970s, when transportation and power generation were "essentially tied" as sources of carbon pollution, DeCicco writes.
But after the 1973 Saudi-led oil embargo and the Iranian revolution in 1979 caused fuel shortages and led to long lines at the gas pumps, the government upped fuel-efficiency standards, and drivers began switching to smaller, lighter vehicles. At the same time, electrical demand was growing, and utilities supplied it chiefly by burning coal. That made smokestacks the biggest source of carbon.
But since 2007, emissions from power generation have been dropping by a rate of 2.8 percent per year, according to DeCicco. The initial cause was the economic downturn, which slowed down factories and caused homeowners to watch their consumption more carefully. After the economic recovery began, cheap, abundant natural gas -- much of it produced by the controversial practice of fracking -- began to supplant coal as a power plant fuel source, and renewable, low-carbon sources such as wind and solar grew as well. As a result, carbon emissions from power plants dropped from 2.5 billion metric tons in 2007 to 2 billion tons in 2015.
Fuel efficiency standards for vehicles have increased also, but since 2012, a stronger economy and a drop in gasoline prices have encouraged more driving, according to DeCicco's analysis.
According to the Federal Highway Administration, U.S. motorists drove 3.1 trillion miles in 2015, an all-time record. To equal that distance, it would take 337 round trips from Earth to Pluto.
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As DeCicco sees it, this shift creates a new policy problem for government officials trying to curb carbon emissions to fight climate change.
"Beyond motor vehicle standards -- the only policy demonstrably effective to date for curtailing transportation CO2 emissions at a national scale -- what else should be done to mitigate the sector's contribution to climate disruption?" he writes.
A switch to electric vehicles would help cut carbon pollution, but they've caught on slowly. A report issued earlier this year by Bloomberg New Energy Finance projects that EVs won't be competitive in price with gasoline-powered cars until at least 2020, according to Wired.
Technology Review writer Mike Orcutt suggests that it may take an increase in gasoline prices to reduce consumption and curb the carbon coming out of tailpipes.
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