You're probably referring to an article in the May 17, 2008 issue of Lancet, a respected medical journal, written by two researchers at the London School of Hygiene & Tropical Medicine. They seemed to be serious, and they aren't the first scientists to consider how obesity contributes to global warming. In 2006, the New York Times reported that a University of Illinois engineer calculated that it takes an extra billion gallons of gas per year to transport overweight Americans. A year before that, the Times article said researchers from the U.S. Centers for Disease Control and Prevention figured that based on the extra 10 pounds the average American gained in the 1990s, the airlines needed to use an additional 350 million gallons of fuel, which added an extra 3.8 million tons of carbon dioxide to the atmosphere.
The London researchers noted that the world's population generates about 42 billion tons of greenhouse gases per year, of which 1.4 billion tons comes from food production. If 40 percent of the population is overweight or obese – as is the case in the UK – the demand for food increases by 18 percent, which pushes up greenhouse gasses from food production by about 260 million tons.
Some experts have proposed simple measures to reduce global warming and obesity at the same time. One, publicized in 2007 by the Associated Press, advocated that all Americans between 10 and 74 walk for half an hour a day instead of driving (I hope no 10-year-olds are driving.) Supposedly this would reduce carbon dioxide emissions by 64 million tons, save 6.5 billion gallons of gas, and result in a national weight loss of more than three billion pounds.
The AP also reported that in 2005, Paul Higgins, a scientist and policy fellow with the American Meteorological Society, calculated that the average person walking half an hour a day instead of driving would lose about 13 pounds a year. And if everyone did that, we would burn a total of 10.5 trillion calories and cut carbon dioxide emissions by about the same amount that New Mexico produces annually.
I can't say if all these numbers add up,and I understand the position of those who maintain that just raising the possibility of obesity's effect on global warming further stigmatizes the obese. But if this information motivates anyone to cut calories and walk instead of drive, it may serve a purpose. Bear in mind that we're all responsible for global warming, and we all have a responsibility to do what we can to reduce our personal carbon footprints.
Andrew Weil, M.D.