Recent research has shown that over the next few decades an effective U.S. climate policy to significantly reduce greenhouse gas emissions would rely on extensive reductions in energy use and substitution of natural gas for coal in power generation. The second pathway - gas-for-coal - is premised on the fact that natural gas, when combusted, produces 50 percent lower CO2 emissions than coal.

A recent paper by Cornell Professor Robert Howarth and others in Climatic Change Letters calls the gas-for-coal solution into serious question, suggesting that natural gas power generation is twice as greenhouse gas (GHG) intensive as coal. Howarth bases this conclusion in part on his assessment of methane leakage in the production stages of natural gas, with a specific focus on new methods to produce unconventional shale gas. [...] The Howarth study raises some legitimate questions about the uncertainties surrounding associated estimates of methane emissions - but Howarth's conclusions depend on a couple of unsound assumptions. [...]

Reduced energy use and coal-to-gas substitution could provide a bridge to a low carbon future, enabling us to move forward on climate change mitigation while we continue critical research on other more advanced technologies. Energy alternatives require close scrutiny for their range of impacts on the environment - the environmental effects of shale gas are no exception.

It would, however, require much more compelling evidence and analysis to persuade us that we should actually use more coal and less natural gas power generation, a logical conclusion from Howarth's paper. Calculations that test conventional wisdom are important in driving further scrutiny. The preponderance of the evidence, however, continues to support the conclusion that substitution of gas for coal in power generation is an important component of a sensible and effective near-term climate change policy.