Cities and Climate Change: Greening the Concrete Jungle

The Economist

America’s cities are confronting climate change. They are also saving money.

THERE are many places in Illinois where you expect to find a prairie. The roof of City Hall in Chicago is not among them. Yet there it is—20,000 square feet (almost half an acre) of shrubs, vines and small trees, 11 storeys above LaSalle Avenue. Planted in 2000, City Hall’s “green roof” reduces the amount of energy needed to cool the building in the summer; captures water during rainstorms, thus reducing the amount of water flowing into Chicago’s already overtaxed sewers; and combats the urban “heat island” effect, which makes cities warmer than nearby rural areas. On average, air temperatures above City Hall are 10-15°F degrees lower than those above the adjacent black-tar roof of the Cook County Building; on hot summer days the difference can be as great as 50°F.

Large as it is, City Hall’s roof accounts for a small proportion of Chicago’s total green-roof space. And those roofs are just one part of Chicago’s Climate Action Plan (CCAP), which was launched in September 2008 and was preceded by years of green initiatives during the tenure of Richard Daley, who from 1989 until earlier this year was mayor of Chicago. CCAP aims to reduce Chicago’s greenhouse-gas emissions to 75% of their 1990 levels by 2020, and to just 20% of their 1990 levels by 2050. In the two years after CCAP’s launch public-transport ridership rose, millions of gallons of water were conserved, hundreds of hybrid buses were added to Chicago’s fleet and over 13,000 housing units and nearly 400 commercial buildings were retrofitted for energy efficiency.