If all goes well, the project will absorb nearly 10,000 tons of CO2 (and 57 tons of other pollutants) on a yearly basis, and pump out 900 tons of oxygen in the process. This isn't some far-off dream, either, as Boeri's firm expects to complete the Forest City by 2020.

Just don't count on these eco-friendly cities becoming ubiquitous. Even if municipalities are fine with retrofitting existing buildings, they'll still need ideal climates to support all that flora. There's a good reason why Boeri's team is setting up in southern China -- it's easy to maintain plant life in an area which rarely deals with freezing temperatures. Nonetheless, this hints at a future where entire population centers fight air pollution and leave a relatively tiny mark on the environment.