[thedoc (OP)]

When talking about sustainable architecture you listen about green walls and roofs and urban agriculture. It's claimed that plants absorb the CO2 and the pollutants from the atmosphere, wouldn't it be the same for the crops that we will later eat?
Asked by Maria Gabriella

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[chapter podcast=1000679 track=14.04.29/Naked_Scientists_Show_14.04.29_1002248.mp3]  ...or Listen to the Answer[/chapter] or [download as MP3]

[CliffordK]

There are buildings with plants growing on the roof or a "green roof".  It may well help absorb some pollutants.  As far as carbon sequestration, it all depends on what happens to the plant matter, but it just grows, dies, decomposes, and regrows, then any carbon captured would become part of a cycle, with no increasing net sequestration. 

One might be able to grow crops on the roof, again generally with an annual cycle for the CO₂, unless somehow the organic matter is buried deep below the surface of the earth.