Urban centers lie at the root of an important, and often neglected, source of emissions: deforestation. According to senior researcher Tom Prugh in "Can a City Be Sustainable?", the latest edition of the annual State of the World series from Worldwatch Institute, Washington, D.C., deforestation caused by growing urban consumption is contributing to massive emissions globally, despite increasing sustainability efforts locally.
Tropical deforestation accounts for an estimated 3,000,000,000 tons of carbon dioxide per year-equivalent to the emissions of some 600,000,000 cars--according to researchers at Winrock International, Little Rock, Ark., and the Woods Hole (Mass.) Research Center.
Urban growth drives deforestation in at least two ways. First, as rural migrants to cities adopt city-based lifestyles, they tend to use more resources. Their incomes rise and their diets shift to a greater share of animal products and processed foods. This, In turn, drives land clearance for livestock grazing and fodder, either locally or in other countries that export such products. Meeting the food needs of a rising and urbanizing global population could require an additional 2,700,000 to 4,900,000 hectares of cropland per year.
"In Brazil [site of last month's Summer Olympics], a surge of deforestation in the Amazon in the early 2000s has been attributed to the expansion of pasture and soybean croplands in response to international market demand, particularly from China," says Prugh. There, economic growth and diets richer In meat products have boosted soy imports from Brazil to feed pork and poultry.
Even in relatively highly productive European agriculture, it takes an estimated 0.3 square meters of farmland to produce an edible kilogram of vegetables, but 7.3 for chicken, 8.9 for pork, and 20.9 for beef.
A second, and likely lesser...