  We need enough new carbon sinks to 1) cancel out any continuing use of fossil
fuels, 2) overcome the delayed effect of earlier excesses, and then 3) lower
atmospheric CO2 concentrations to the old maximum value of 280 ppm. We need to
sink about 25 billion tonnes of carbon each year, half to counter current
emissions and commitments, and half for drawing down the CO2 concentrations
within a few decades. A very large carbon sink could be created by sinking
sewage in offshore dead zones. Half of all people live close enough to a coast
to personally contribute, making the sink size close to half the annual food
production.
