OPPOSITION to fracking has been considerable, if not unanimous, in the global green community, and in Europe in particular. France and Bulgaria, countries with the largest shale-gas reserves in Europe, have already banned fracking. Protesters are blocking potential drilling sites in Poland and England. Opposition to fracking has entered popular culture with the release of “The Promised Land,” starring Matt Damon. Even the Rolling Stones have weighed in with a reference to fracking in their new single, “Doom and Gloom.”

Do the facts on fracking support this opposition?

There is no doubt that natural gas extraction does sometimes have negative consequences for the local environment in which it takes place, as does all fossil fuel extraction. And because fracking allows us to put a previously inaccessible reservoir of carbon from beneath our feet into the atmosphere, it also contributes to global climate change.

But as we assess the pros and cons, decisions should be based on existing empirical evidence and fracking should be evaluated relative to other available energy sources.

What exactly is fracking, or more formally hydraulic fracturing?

Many sandstones, limestones and shales far below ground contain natural gas, which was formed as dead organisms in the rock decomposed. This gas is released, and can be captured at the surface for our use, when the rocks in which it is trapped are drilled. To increase the flow of released gas, the rocks can be broken apart, or fractured. Early drillers sometimes detonated small explosions in the wells to increase flow. Starting in the 1940s, oil and gas drilling companies began fracking rock by pumping pressurized water into it.