IMAGE IS FOR YOUR ONE-TIME EXCLUSIVE USE ONLY FOR MEDIA PROMOTION OF THE MAY 2009 ISSUE OF NATIONAL GEOGRAPHIC MAGAZINE. NO SALES, NO TRANSFERS.©2009 Diane Cook / Len Jenshel / National GeographicA garland of nature crowns Chicago?s City Hall, softening the hard edges of a town famous for steel and stone?and lowering summer temperatures on the roof. Inspired by a worldwide movement, Mayor Richard Daley has made Chicago North America?s leading ?green roofs? city.

IMAGE IS FOR YOUR ONE-TIME EXCLUSIVE USE ONLY FOR MEDIA PROMOTION OF THE MAY 2009 ISSUE OF NATIONAL GEOGRAPHIC MAGAZINE. NO SALES, NO TRANSFERS.

©2009 Diane Cook / Len Jenshel / National Geographic

A garland of nature crowns Chicagoâ??s City Hall, softening the hard edges of a town famous for steel and stoneâ??and lowering summer temperatures on the roof. Inspired by a worldwide movement, Mayor Richard Daley has made Chicago North Americaâ??s leading â??green roofsâ? city.