Christopher Yang, transportation engineer

A young engineer explains why emissions from our beloved cars threaten California’s future—and what we can do about it. Interview by Sascha Zubryd

March 28, 2011

Photo courtesy of Christopher Yang

Transportation expert Christopher Yang studies greenhouse-gas emissions from trains, planes, and automobiles—anything that uses fuel to move. Exhaust-belching vehicles produce nearly half of California’s carbon emissions, while the emissions in other states come mostly from factories and energy-guzzling heaters and air conditioners. Powering vehicles with alternative energy sources—like biofuels, hydrogen, and electricity—could reduce California’s transportation emissions by a whopping 60 percent, according to Yang’s research with California’s Energy Future committee.

That’s good news because California faces a major challenge: former Governor Arnold Schwarzenegger's 2005 executive order to slash greenhouse-gas emissions to just one-fifth of 1990 levels by 2050. The state is headed for warmer average temperatures and more hot days, which means a shrinking snowpack. That could spell serious trouble for water supplies. Stabilizing greenhouse-gas levels in the atmosphere would help steady the local climate, scientists expect. Researchers like Yang have been scrambling to project how to reach the target.

Yang’s passion for environmental conservation began in high school. “When I was trying to figure out who I was, water and energy issues and global warming were becoming more public,” he says. “It left an imprint on me.” He earned his Ph.D. in mechanical engineering in 2003 at Princeton University, where he studied fuel cells. Now he’s a research scientist at the University of California, Davis Institute of Transportation Studies, in the Sustainable Transportation Energy Pathways program.

Yang’s work suggests that to meet the 2050 target, California’s transportation emissions must shrink by at least 60 percent—a tall order. At the February 2011 meeting of the American Association for the Advancement of Science in Washington, D.C., Yang and SciCom's Sascha Zubryd discussed the challenges of cleaner transportation.

First of all, why is it important to reduce greenhouse-gas emissions?

The main issue is the impact on climate change, and California is vulnerable to climate change. Changing snow pack, which is a big part of our water supply, is going to be a huge issue, and water is already a big problem in California. There are also the impacts on the state’s natural ecosystems and wildlife. I think transportation will play a pretty big role in any plan to reduce greenhouse gas emissions.

By executive order, California has to reduce its emissions drastically by 2050. How does reducing emissions from transportation figure into that?

Every sector of the economy does not have to do an equal share of emissions reduction. There’s buildings, industrial energy use, transportation, and other things as well. Each has different costs associated with reducing emissions. A lot of models say transportation is a fairly expensive way to reduce emissions. However, since transportation is the largest contributor, it needs to reduce emissions quite a bit. A lot of people may have thought if we just go to renewables, or if we just have nuclear power, that would be enough. But it’s clear every sector needs to play a role.

Does it actually make any difference if I take public transit to work instead of driving?

Definitely. Taking public transportation makes a difference because that bus or train will be running regardless of whether you’re on it. So by taking it, you’re not adding any emissions or energy use to the system. You’re eliminating the emissions you would have generated by taking your car. Obviously, if everyone took public transportation, you would require more buses, more trains to be run. But buses and trains are more efficient per mile for each passenger than a car. So even though you would add more bus emissions, you would subtract many more car emissions, so there’s still a benefit. Electric vehicles are also much more efficient than conventional gasoline cars—about four times more efficient.

What do you mean when you say electric vehicles are more efficient?

They use less energy per mile traveled. A gallon of gasoline is equivalent to, in technical terms, 33 kilowatt-hours of electricity. That means if you burn a gallon of gasoline, or if you consume 33 kWh of electricity, you produce the same amount of heat. [33 kWh is enough to power a typical 100-watt light bulb fortwo weeks straight.] But an electric car can go much farther on 33 kWh of electricity than a gasoline car can go on a gallon of gasoline.

"With the political climate it seems challenging to even meet modest goals [to reduce greenhouse-gas emissions]. Somebody’s got to be responsible for making your home electricity bill go up. Who’s going to vote for that person?"

Making passenger vehicles electric is one thing. What can we do to lower emissions from other kinds of transportation?

Some other forms of transportation can also be electrified, like buses and trains, and electricity can be decarbonized. In California we have a Renewable Portfolio Standard that requires 33 percent of generation from the big utilities to come from renewables [solar, wind, or biofuels]. The beauty of electricity is that there are policies and mandates in place for electricity providers like PG&E and Southern California Edison to reduce greenhouse gas emissions over time. So your electric car is going to get cleaner just because it’s using electricity, regardless of what you do as a consumer. If we’re serious about meeting the 2050 goal, electricity carbon emissions basically have to go to zero.

Hydrogen is also a form of electrification. Electricity produced in a hydrogen fuel cell powers the vehicle in place of electricity from a battery.

Some types of transportation don’t lend themselves to electrification, like airplanes, heavy trucks and boats. However, you can still make these vehicles very efficient and power them with low-carbon fuels like biofuels.

What do you see as the biggest barrier to reducing California’s transportation emissions?

To reduce emissions from transportation requires a fair amount of buy-in from the consumer. You have to buy an electric car, or use a hydrogen-powered car, or at least change the way you fuel your vehicle. If we were talking about moderate reductions, like 20 or 30 percent, we could probably do it with hybrids. But to get 60 percent reductions, we need these radical, more advanced technologies.

Among the scientific, technological, and political factors, which is the bigger impediment to making progress toward that goal?

It’s a combination of things, but personally, I think with the current political and economic climate it seems challenging to even meet more modest goals. A lot of the options we talk about will increase the cost of energy and the cost of transportation services.

That’s a hard sell.

Not just a hard sell. It may be an impossible sell because some politician has to be responsible for that. Somebody’s got to be responsible for making your home electricity bill go up. Who’s going to vote for that person? Political leaders must convince people these choices are important enough to warrant higher costs. But that’s not to say the technology isn’t important. There needs to be a lot of technological progress and innovation.

What technological advances do we still need?

Engineers are always making car engines more efficient. But that efficiency has been used to move bigger, heavier cars. Raising the price of fuel would be a way to incentivize people to go with a more appropriately sized vehicle. What we need are further policies that will bring about faster improvements—fuel economy standards, fuel price increases, carbon taxes, further incentives for car companies to reduce the amount of fuel their vehicles use. It comes down to economics. Also, the federal government has been making an effort to put money into battery research, fuel cell research, and hydrogen storage research.

What about subsidizing the cost of the actual vehicles if people choose to buy vehicles with better fuel economy?

There’s a really good policy instrument called a “feebate.” It’s a combination of a fee and a rebate. The idea is you set a value, say 30 miles per gallon, as your middle point. Cars that get above that value in terms of fuel economy get a rebate, and cars below it have to pay a fee. You can still buy a sports car that gets 12 miles per gallon if you want, you just have to pay an additional fee, and you’re helping to subsidize people who are choosing to buy a hybrid. It’s a nice idea to work within the light-duty vehicle market so people can get an instant rebate or instant fee at the time of purchase.

At UC Davis, you look at both environmental and economic factors involved in greenhouse-gas emissions from transportation. What’s unique about the way the Sustainable Transportation Energy Pathways program approaches these issues?

We have such a wide variety of expertise in transportation. We actually have an anthropologist on staff. We also have economists, engineers, all the usual people. We try to understand the potential for these advanced vehicles and alternative fuels from a lot of different perspectives. We do demonstrations where we convert some Toyota Priuses into plug-in vehicles and give them to a household for a month and let them drive it around. We do extensive interviews before and after. It’s also outfitted with GPS so we can get a detailed understanding of how they used the vehicle. As an engineer, I mostly just deal with models and numbers, but it’s really nice to talk to researchers doing consumer-facing studies.

How would you summarize all the things we’ve talked about that figure into reducing transportation emissions?

Scientists use an equation called the Kaya equation when we look at emissions from transportation. It’s very straightforward. It breaks emissions from transportation into four terms.

The first term is Population. The second term is Transportation Intensity: the amount of travel per person. The third term is Energy Intensity: the amount of energy used to go one mile. The fourth term is Carbon Intensity: the amount of greenhouse gases per unit of energy.

It’s a multiplication equation, so if you double population, you double emissions. If you have some magic biofuel and can get the Carbon Intensity to zero, then it doesn’t matter what you do with everything else. Your emission will be zero because zero times anything is zero.

Obviously it’s not quite as simple as that, but the idea is that you can reduce the amount of travel people need to do, you can reduce the amount of energy used to do that travel, or you can reduce the amount of carbon that’s used. Each of those terms is quite important. Any solution will involve all of them.

Why is your work important to you?

As a young person living in a dorm or at home you might not have much say in the building’s energy use. But transportation is tangible for everyone. You can decide whether you drive, carpool or take public transportation. My graduate work on fuel cells had a natural link to transportation because it’s a way to apply the technology. People are becoming more aware of climate change now, and policymakers need advisors. It’s where my expertise lies, and I feel like I can make a contribution.

Sascha Zubryd, a 2011 graduate of the Science Communication Program at UC Santa Cruz, earned her bachelor's degree in psychology from UC Davis. She has worked as a reporting intern at the Stanford University Medical School news office, the Santa Cruz Sentinel, and the Woods Institute for the Environment at Stanford. She is now working as an exhibit-design intern at the San Francisco Exploratorium.

© 2011 Sascha Zubryd