The Pacala and Socolow wedges vision focused on what can be done to help the climate by reducing emissions below BAU. However, the range of policy and technology choices available that are not included in BAU assumptions includes a number of options that could raise emissions significantly. These are likely to be driven particularly by energy security concerns and/or consistently high oil prices, and include:

  • Production of synthetic liquid fuels from coal (known as coal-to-liquids, or CTL),
  • Extraction of heavy oils from so called “tar sands,” and
  • Production of oil from crushed rocks called “oil shale.”

Considering oil security issues in isolation, these options offer some advantages: although high-cost, they depend on fuels that are available in abundance in countries such as the United States and Canada. However, from a climate perspective they represent a serious threat. Employing CTL would nearly double the emissions of petroleum-based fuels, and both tar-sands and oil-shale require vast amounts of energy and water to process. Extensive application of one or more of these technologies could have fatal effects on efforts to limit climate change.

In this report we term these “threat wedges” to contrast with the “smart wedges” of the Pacala and Socolow vision. This figure shows how these expand the range of technology considerations that we need to confront, and the risk that some policy and investment choices could actually cause emissions to rise dramatically above business as usual, negating the beneficial effects of the clean technology smart wedges.

Note: this chart is a revision of the original version in the publication.