a study published recently in Global Change Biology found that rainforests have been displaced as ecosystems that store the most carbon- by cities! cities store more carbon in their trees, buildings and dirt, than the densest and most productive tropical rainforests.
according to researcher Galina Churikina, who led the study, US cities store about 20 billion tons of organic carbon. most of this carbon is held in soils, though a sizable fraction is also contained within buildings constructed with wood. ironically, the key to city’s’ remarkable capacity to store carbon seems to be their artificial nature. buildings and asphalt “bury” soils, locking away carbon that was once part of a dynamic forest, grassland, or other natural ecosystem.
this is not to discount the importance of urban trees in both storing carbon and providing numerous ecosystem services. trees and other urban plants ameliorate temperatures, providing a cooling effect in summers that reduces the need for air conditioning. trees also directly take up CO2 emitted from cars, reducing the amount of pollution that enters the atmosphere from cities in the first place.