Since Hillary Clinton announced her support last week for suspending the federal gas tax between Memorial Day and Labor Day, the press has marshaled economists and environmentalists from around the country to wholeheartedly denounce the idea. Of course, it’s not really the soundness of the plan that the media are after, or else they would have mounted a similar charge when Republican John McCain called for the gas-tax “holiday” in mid-April. Journalists jumped into action this time because Clinton’s proposal created a situation in the Democratic party that is no longer possible on the GOP ticket: division.

Division between Clinton and Barack Obama, who has called her gas-tax proposal a political “gimmick,” is a good thing, though, especially when it comes to energy issues, upon which they have mostly agreed until now. As evidenced by the lack of critical attention to McCain’s call to suspend the 18.4-cent federal tax, however, the press often doesn’t get around to teasing out division until it is blatantly obvious (and in this case, perhaps, short-lived, after Clinton’s anemic performance in Tuesday’s primaries).

That’s too bad, because the recent debate about the gas tax hints at a parallel and equally important, but largely unexplored facet of the cap-and-trade legislation that both Clinton and Obama (and McCain for that matter) support: the so called “safety-valve” clause.

One of the reasons that the safety-valve clause hasn’t received much attention from the media is that it’s nominally a feature of the Low Carbon Economy Act, a cap-and-trade bill sponsored by Senators Jeff Bingaman, a New Mexico Democrat, and Arlen Specter, a Pennsylvania Republican. The safety valve guarantees American companies that the price of one carbon credit (which is a permit to emit one metric ton of carbon dioxide or its equivalent in other greenhouse gases) will not rise above $12 in the first year, and increase 5 percent annually beyond inflation after that.

The Bingaman-Specter legislation has not received anywhere near the amount of coverage that the stricter, but more popular Climate Security Act has gotten. The Act, which was introduced by senators Joe Lieberman, a Connecticut independent, and John Warner, a Virginia Republican, doesn’t have a safety-valve clause, but it has something similar - a Carbon Market Efficiency Board that will release credits to bring down the cost of polluting if the price of emissions gets too high and threatens the economy.

The safety valves in the two pieces of legislation are different from the gas-tax holiday in many respects, but essentially they’re all designed to pull the plug on high carbon prices if Americans (especially those in the lower economic strata) begin to struggle financially. And ultimately, both the safety valves and the gas-tax holiday favor consumers and benefit the fossil-fuel industry by hobbling, to some degree, programs that were designed to facilitate the shift to renewable sources of energy. Thanks to the last week of electoral bickering, we know how each of the candidates feels about suspending the gas tax, but what about the safety valves in the two cap-and-trade bills?

Clinton, Obama, and McCain all support some form of cap-and-trade legislation. Clinton voted for the Lieberman-Warner bill in an Environment and Public Words committee markup, but Obama’s and McCain’s inclinations are still unclear. Regardless of political backing for either bill, though, the press has failed miserably at comparing them in any useful or analytical way. There have been reams of stories, of course, that dissected the cap-and-trade system more generally and compared it to a carbon tax, which is an alternative emissions reduction strategy. Few journalists have picked apart any of the fine differences between various forms of cap-and-trade, however.

Last week, Ceres, a coalition of investors that pushes companies to reduce emissions, and the National Resources Defense Council, released a little-noticed report that specifically compared the financial impacts, on power companies and consumers, of the Climate Security and Low Carbon Economy Acts. According to Ceres’ chief press officer, Peyton Fleming, the group based its calculations on a carbon emission price of $10 per ton, an admittedly low value, in part because of the safety valve clauses in the two bills. “We recognize that the cost of emissions is likely to be higher,” he said in an interview, “but we didn’t want to use that immediately and have [the bills’ sponsors] turn around and complain that safety valve will keep prices down.”

Curtis Brainard writes on science and environment reporting. Follow him on Twitter @cbrainard.