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## Socolow and Pacala, Scientific American 0609, “A Plan to Keep Carbon in Check”

• Two years previously, the authors developed the concept of a carbon wedge, which is a triangle representing the difference in carbon emissions between 2006 and 2050 for two development paths: business as usual and a proposed carbon-lowering technology. A wedge has a height of 1 billion tons/year and a base of 50 years, for a total of 25 billion tons. To hold peak carbon dioxide levels below a peak of 560 ppm (twice the pre-industrial value), we need (at least) seven wedges.
• Potential wedges
1. Efficient lighting and appliances (2 wedges)
2. Carbon capture and storage at 800 large coal-fired plants (1 wedge)

See the graphic on page 54 for 15 potential wedges.

• We estimate that the price needed to jump-start the transition to CCS is in the ballpark of $100 to$200 per ton of carbon. This level of tax is comparable to the subsidies for new renewable and nuclear energy, and half the subsidy of ethanol. A tax at $100/ton of carbon is$12 per barrel of oil and \$60 per ton of coal, which is equivalent to 25 cents/gallon of gasoline and 2 cents per kWh of electricity from coal.
• In 2006, roughly half of all carbon emissions are from OECD states and half from developing countries and countries from the former Soviet Union.