As the Olympic Games draw near in London and some fret about the environmental impact, it might be instructive to look back on the measures taken when Beijing played host in 2008.  It’s not likely that the organizers in Beijing were thinking about climate change when they ordered large numbers of cars and trucks to stay out of the city before the games began. One suspects that they were more worried about harm to the country’s image, if the world watched athletes struggling to compete while inhaling dirty air.  Still, it stands to reason that if you drastically cut the number of vehicles in an urban center, you will reduce not just the carbon monoxide and the smog that chokes runners but also the carbon dioxide that helps trap heat in the atmosphere.  Four years later, scientists led by Helen M. Worden at the federal government’s National Center for Atmospheric Research have roughly quantified the extent to which the Beijing government’s temporary crackdown on urban traffic reduced carbon dioxide levels. Even with significant uncertainties factored in, the amount is striking. An effort by one city (the world’s 19th most populous metropolitan area, with 12.5 million people) led to emissions reductions that, if made permanent and multiplied by 360, would be enough to avoid the concentrations of greenhouse gases that could lead to dangerous levels of warming.  Imagine what could happen if bigger metropolitan areas like Tokyo (32.4 million people) Seoul (20.5 million) Mexico City (20.4 million) New York (19.7 million), Mumbai (19.2 million) and Jakarta (18.9 million) did likewise?  ““This implies that sustained controls on urban transportation emissions, on the scale implemented in Beijing, could potentially provide a significant part” of emissions reduction, the authors write. They cautioned that they were not addressing “the sustainability of these controls or the feasibility of applying traffic restrictions in other cities.”  The findings by the researchers, from the atmospheric research center, the University of Iowa, Tsinghua University in Beijing, the Argonne National Laboratory and Caltech, did not break new ground in concluding that Beijing’s strategy — which included banning half of all privately owned cars form the city, halting much construction and temporarily shuttering some factories — cut pollution.  The groundbreaking element was the computer programs they used to analyze data from a satellite-based radiometer that has been measuring carbon monoxide on the earth’s surface for a dozen years.  The final measurements had a wide margin of error: the total carbon dioxide reduction in Beijing during the Olympics was anywhere from 24,000 metric tons to 96,000 metric tons. Yet however rough, the data was more precise than earlier measurements taken through inventories of ground-based emissions.  “When they made these traffic restrictions, we knew the air was better as a result,” Dr. Worden said in an interview. “But how much better? Would that make a difference? Would it be a drop in the bucket, or a substantial cut?”  The answer, she said, was definitely the latter. “If all the urban populations did this, it would almost get us there,” she said.  The goal Dr. Worden was referring to was reducing greenhouse gases in the atmosphere to a point that would prevent the planet from heating by more than 3.6 degrees Fahrenheit — a kind of scientific Maginot line for the crossover to a dangerously warm planet.
A new study gives the first rough estimate of how the Chinese reduced carbon dioxide emissions from urban traffic during the 2008 Olympic Games in Beijing.