This month, Gasland Part II is showing on HBO. The documentary by Josh Fox is the follow up to his original movie a few years back on the dangers of using hydraulic fracturing, or fracking, to extract natural gas.

When the first movie came out in 2010, most people hadn't even heard of fracking, a process that injects chemicals and millions of gallons of water into rock to release natural gas. But in the last five years, gas companies have bought leases in 34 states on land that totals the size of California and Florida combined so they can frack, Fox said in a recent interview. That kind of expansion surely means that many more people know something about fracking now.

Certainly the push to make the U.S. energy independent as well as less reliant on U.S. coal, a big generator of greenhouse gases and other air pollutants, have made cheap natural gas look very attractive, and it would be easy to dismiss Fox's latest production as another misguided attempt to stand in the way of progress. Critics say Fox makes inaccurate and misleading claims.

But less sensational efforts continue to raise questions about fracking. For example, a study reported on in the July 9 issue of the Proceedings of the National Academy of Sciences found that some homes located less than 1 kilometer from gas wells in the Marcellus Shale region in northeastern Pennsylvania and southeastern New York had their drinking water contaminated with stray gases. And in a review published today in Science, researchers say the fracking process is capable of causing earthquakes.

Nevertheless, others say fracking is getting safer and bigger companies are doing the best job of making that happen. Certainly industry representatives say the technology is safe.

The point is that fracking has positive and negative implications for millions of people, and it needs to be thoroughly debated and studied. A cheap source of domestic energy for the U.S. is important, but even more important are protecting the health of the population and evaluating the long-term effects on the environment of drilling more gas wells. I haven't seen Gasland II yet, but I give Fox credit for raising awareness and stirring the national debate at a time when the federal government is backing away from the issue.