Ann Arbor, Michigan – U.S. automakers must achieve an eightfold reduction in auto-related carbon emissions to help stabilize the amount of heat-trapping carbon dioxide in the atmosphere by 2050, according to researchers at the University of Michigan (U-M).

A research team looked at what it would take to reduce emissions to help stabilize carbon dioxide levels at a concentration of 450 parts per million by 2050, which it said would avert many of the most serious consequences of human-caused climate change. Currently, U.S. passenger vehicles emit about 160 grams of carbon for every mile driven, including tailpipe emissions and carbon associated with fuel production. That number must be reduced to 20 grams per mile, the researchers said. The study appears in the journal Environmental Science & Technology.

According to Greg Keoleian, centre co-director of the U-M School of Natural Resources and Environment, improved fuel efficiency, the widespread use of low-carbon fuel, and a change in driving habits have all been suggested as ways to reduce carbon emissions, but no single approach will suffice. To achieve the reduction targets by adopting just one of these approaches would require automobiles with an average fuel economy of 136 m.p.g., an 83 per cent market share for low-carbon ethanol, or a 53 per cent reduction in U.S. travel demand by 2050, according to computer model simulations.

“Any individual vehicle carbon-reduction strategy is not likely to be successful in the long term,” Keoleian said. “To meet these targets, we need a combination approach that tackles all these factors simultaneously. Most importantly, we need a transformed energy system. Basically, we have to shift our emphasis on fossil-based fuels to renewable and, in the interim, there might be more of a role for nuclear. At the same time, we need to dramatically ramp up our fuel economy and reign in vehicle miles travelled.”

In the U.S., transportation accounts for about a third of all greenhouse gas emissions, while automobiles are responsible for two-thirds of transportation sector emissions.

The researchers said that while several manufacturers have announced plans to build plug-in hybrid cars, they will merely shift a portion of the carbon emissions from the vehicle to the power plant if the electricity is generated at a coal-fired plant. Significant overall reductions will require big reductions in the use of fossil fuels for power generation and for liquid vehicle fuels, and an increased reliance on renewable energy sources such as wind or solar, as well as nuclear power, will be necessary.