How Does the Global Warming Pollution from Cars Compare to Other Major Sources Such As a Coal Power Plant?
Ask a Scientist - May 2010
S. Tompkins from Charlotte, NC, asks "How does the global warming pollution from cars compare to other major sources such as a coal power plant?" and is answered by Clean Vehicles Senior Engineer Jim Kliesch.
Looking at the big picture, about a third of U.S. global warming pollution comes from moving vehicles: passenger cars and trucks, big rigs, airplanes, trains, waterborne shipping, etc. Passenger cars and trucks are the biggest slice of that pie just because of the sheer number of them we have on the road.
In broad terms, the environmental impact of a vehicle is affected by three things:
- the emissions from producing the vehicle
- the emissions from operating the vehicle
- the emissions associated with the vehicle’s fuel (see below)
Typically, the production of a vehicle accounts for only about 20 percent of its overall environmental impact, so for our purposes, I’m going to focus on emissions from the vehicle and fuel.
While your question is focused on global warming pollution, it’s important to note that there are key differences between smog-forming pollutants and global warming pollutants when it comes to cars. The amount of smog forming pollution your car produces depends on a device called a catalytic converter, which is essentially a washing machine that cleans your exhaust before it exits the tailpipe. There’s no corresponding device to clean global warming emissions, such as carbon dioxide (CO2), from your car.
So the global warming pollution from passenger cars and trucks is therefore largely related to how much fuel they burn. There are direct emissions, which come from combusting fuel in the engine, that create about 19 pounds of CO2 per gallon of gasoline burned. And there are “upstream” emissions, which come from the extraction, refining, and transport of the fuel from the well head to the gas station pump, that create another 5-6 pounds of CO2 per gallon. Before you even start your car, you’re already responsible for the emissions produced by transforming that fuel from crude oil to the gas in your tank. So, when you add up the direct emissions with the upstream emissions, a gallon of gasoline is responsible for close to 25 pounds of CO2.
With this in mind, a passenger car or truck today is typically responsible for around 7.4 tons of CO2 a year. If you compare that to a typical, existing 600 megawatt coal plant, producing 5.2 million tons of CO2 pollution a year, then, in one year, that plant is producing as much global warming pollution as around 700,000 cars. (This assumes the plant does not use carbon capture and storage technology, which has yet to be demonstrated in the form of commercial-scale, fully integrated projects at coal-fired power plants.)
But be sure to note the reference to "in one year." Often, when people talk about something that emits a lot of pollution, they’ll say “if we manage to stop it, it would be like taking X cars off the road,” and that’s all it says. There’s a big difference between taking those cars off the road completely and taking them off the road for one year. A new vehicle is driven about 15,000 miles per year and burns the corresponding amount of fuel. On the other hand, if you take a vehicle off the road entirely, 150,000 miles of travel – or more – would be avoided.
But what’s clear from all of this is that we are producing way too much global warming pollution in both the transportation and the energy sectors. At the end of the day, it’s going to take a diversified effort—including efficiency improvements, a shift to clean energy, and development of clean fuels and advanced vehicle technologies, among others—if we are to reach the kind of global warming emissions reductions that scientists say are needed to avoid the worst effects of climate change.
Jim Kliesch is an engineer with expertise in clean and efficient vehicle technologies. He holds a bachelor's degree in electrical engineering from Ohio University, and a master's degree in environmental and energy policy from the University of Delaware.
