http://gristmill.grist.org/story/2007/2/22/17152/5926#5

The real winning "device"?  Conservation land and organic farming.  Mega-devices.

Prairie National Park (and windfarm).  And biogas digestion to make organic fertilizer.

7 million square miles of prairie would sequester all present uS CO2.  Too big?!  Yes, but using organic farming and conservation land could still sequester one third.  And plugin cars, wind/wave power, solar,biogas, and conservation could eliminate most  of present cO2.

So the sequestration land could actually remove CO2 already in the atmosphere on a net basis.