One result of Super Tuesday’s primary elections has gotten very little coverage. With those results, the world nudged ever closer to finally — finally — grappling with what is arguably our greatest shared challenge, global warming.

Consider: While Mitt Romney and Mike Huckabee say they’ll remain in the race, Arizona Senator John McCain has clearly emerged as the Republican frontrunner. That makes it likely that the U.S. general election will feature a contest between two candidates who take global warming very seriously, who agree that it’s caused by human activities, and who want to do something decisive to stop it – McCain on the one hand, and either Hillary Clinton or Barack Obama on the other.

The fact that the presidential field has apparently narrowed to these three contenders might seem grounds for planetary rejoicing. However, it’s important to note that despite their broad similarities, when it comes to global warming McCain and the two leading Democrats aren’t perfectly interchangeable.

Certainly, all three want a bill passed that will do something about climate change. Moreover, they want the same kind of bill: so-called ‘cap and trade’ legislation that will set an ever-tightening economy-wide cap on total U.S. greenhouse gas emissions, and empower the government to distribute pollution allowances or permits to all emitters. Companies that wind up emitting less than their allotted amount would be free to trade their remaining permits to others as they see fit. And so, thanks to market forces, the total amount of emissions would steadily decline.

So far so good. But examine the positions of the leading presidential contenders, and differences emerge between McCain and the two Democrats which are almost as large as the difference between McCain and Mitt Romney (who has repeatedly attacked McCain over his strong stance on climate). Those differences could have dramatic implications for the future of the planet and humanity.

Both Clinton and Obama say they want a stringent bill that would cut U.S. greenhouse gas emissions by 80 percent by the year 2050. Those are the kind of deep cuts that scientists say we must have if we want to avoid the worst possible impacts of global warming. The news coming in from the climate system, after all, has been getting more and more alarming – with the record decline in Arctic sea ice observed in summer 2007 perhaps most shocking of all. Scientists now fear that climate change could accelerate far more quickly than expected, in which case we don’t have a moment to lose.

John McCain also supports a cap and trade bill, but there are many reasons to think he’d settle for a policy that is more lenient and compromise-oriented. Notably, McCain worked closely with Senator Joseph Lieberman on climate legislation in the past, and the current bipartisan Lieberman-Warner bill sets a lower target for emission reductions — a 70 percent reduction in capped emissions by 2050 (and not all emissions would be capped).

There’s another major difference between the Democratic and moderate Republican approach on global warming. Clinton’s and Obama’s cap and trade plans would auction off 100 percent of the initial pollution permits, using the proceeds for needed causes like investing in clean energy technologies that will reduce carbon emissions. In contrast, the Lieberman-Warner bill – closer to McCain’s favored approach – would auction off only a small percentage of allowances initially. Major emitters would be granted many allowances to pollute for free at the outset. That’s an idea that leaves some environmentalists tearing their hair out.

McCain’s approach is a good way to get needed support for the bill from industry. But giving away so many allowances not only massively subsidizes special interests, but ignores the principle that the polluter ought to pay for harming the environment.

In essence, then, we’re looking at a classic conflict between idealism and political pragmatism – with the fate of the planet at stake. Moreover, it’s not obvious which approach is more viable: pushing for a moderate Republican bill on global warming that can definitely pass Congress, or pushing for a more ambitious Democratic bill that assures stronger congressional opposition.

Recently, the League of Conservation Voters, a leading environmental organization, launched a campaign to pressure top television talk show hosts to ask the candidates more questions about global warming. Let’s hope that between now and November, journalists and debate moderators see beyond the broad similarities between McCain and the two Democrats on the issue, and press them to explain their differences. For while we now seem fairly assured of a candidate who wants to address global warming in 2009, we still have to decide whether to move slowly or quickly.

Chris Mooney is the author of two books, The Republican War on Science and Storm World: Hurricanes, Politics, and the Battle Over Global Warming.

© 2007 Blue Ridge Press