In order to ensure that participants in the 2008 Olympics could race, leap, and pedal without having to stop, cough, and wheeze, the city of Beijing worked hard to improve its air quality in time to host the summer games. Now, just in time for the 2012 Olympics in London, researchers have crunched the data from the dramatic changes in Beijing air-quality to figure out just how large a role cars and other vehicles play in contributing to greenhouse gas emissions.
While researchers (and most of the rest of us) know that reducing the number of cars on the road should decrease levels of atmospheric carbon dioxide, there’s never been a good way to prove it and quantify the effect. But Beijing’s severely curtailed industrial activity and vehicular traffic provided distinct parameters for them to study, much the same way that the grounding of U.S. air traffic after the September 11, 2001 terrorist attacks gave scientists an unexpected chance to test the impact of contrails on Earth’s climate.
Beginning a few weeks before the opening ceremony, Beijing officials instituted a temporary, alternate-day driving ban, which prevented half the population from driving on any particular day. They also cut industrial activities, suspended construction, and clamped down on gas station emissions. Previous studies have described the ban’s effects on some climate-warming gases, include decreases in carbon monoxide and ozone. Now, researchers have used carbon monoxide reductions to calculate the slow-down’s impact on another major offender: carbon dioxide.
Compared to the same time period the year before, China’s motor-vehicle restrictions reduced carbon dioxide emissions by 24,000 to 96,000 metric tons. If that change had been permanent, it would comprise about 0.25% of the emissions cuts necessary to prevent global temperatures from rising more than 3.6 degrees--the increase widely considered enough to trigger environmental and societal disaster. It’s not that much, but it’s a start. The study, led by Helen Worden of the National Center for Atmospheric Research, was published this week in Geophysical Research Letters.
The authors remain mum on the practicality of applying similar emissions restrictions in other cities, let alone sustaining such strict regulations in Beijing. They do note, however, that “urban traffic controls on the Beijing Olympics scale could play a significant role in meeting target reductions for global CO2 emissions.” What better reason to ride your bike to work?