Synthetic trees solve---we only need 250,000 of them.

A synthetic tree could be planted anywhere. A small one could sit like a TV on the lawn to balance out the CO2 emitted by one person or family. But more practically, said Dr Lackner, a device the size of a barn would sit in the open air, near repositories for easy transportation and storage of carbon. He estimated that 250,000 synthetic trees worldwide would be needed to soak up the 22 billion tonnes of CO2 produced annually.