The major policies used by governments to slow or reverse the growth in a country’s greenhouse gas (GHG) emissions generally fall into four basic categories: economic, regulatory, technological, and forestry/land-use policies.

The fourth scenario is different. For ten years, $250 billion is invested in a trust fund. This trust fund finances a century-long programme of emission abatement such that the NPV of the abatement cost over the century equals $2 trillion. This is achieved by a uniform carbon tax for all countries, which starts at $12/tC in 2010 and rises with the