Storing carbon in cities

Cities have the potential to store vast amounts of carbon, according to a new study. National Geographic reports on the work of Galina Churkina of the Leibniz Centre for Agricultural Landscape Research in Germany:

Churkina and colleagues pulled together previous evidence looking at various stores of organic carbon—carbon that comes from living things, as well as from such as plants and animals, wood, dirt, and even garbage.
Cities—including both dense metropolises and sprawling suburbs—store about a tenth of all the carbon in U.S. ecosystems, the study estimated.
In total, U.S. cities contain about 20 billion tons of organic carbon, mostly in dirt, according to the new study to be published in an upcoming issue of the journal Global Change Biology.

Of all the urban carbon, about three billion tons are locked up in man-made materials - two thirds in rubbish dumps and the rest in building materials like wood. The story continued:

Many cities have already launched ambitious plans for turning gray to green, such as Los Angeles' Million Trees LA project, which aims to plant a million trees in the Californian city over several years.

Building timber instead of concrete houses could also help to sequester carbon, said Leif Gustavsson, an expert on green technology at Mid Sweden University. But he said the main carbon benefit is from the embodied energy of the construction itself, rather than carbon stored in the material.                                     

Meanwhile, earth scientist David Pataki of the University of California stressed that getting urban soils to store more carbon would be a careful balancing act. "Managing urban soils to store more carbon can use energy, and those fossil fuel emissions have to be taken into account," he told National Geographic.