This is the last U.S. election. Have we taken stock of the implications? There is no room for incremental thinking. The storm will fall on whomever we elect president (and isn’t there a case for McCain?). Among the startling implications of breaching the 350 ppm limit is the likelihood that this is the last U.S. presidential election during which there remains a slim opportunity to take decisive global climate action.

All the ordinary rules and habits of elections and campaigning have been summarily and unexpectedly tossed out the window. Building party power, advancing political careers, and addressing climate incrementally are no longer plausible strategies. We must now concern ourselves with electing leaders of character who will rise to the challenge as the crisis begins to unfold and political systems are stressed.

Comparing campaign climate policies, in this context, is not the best measure of candidates. The differences between Clinton, McCain, and Obama on climate are minuscule compared to the gulf between the state of U.S. civic debate and the scale of response required to avert cataclysm. Furthermore, a simple head-to-head comparison of policy takes no account and gives no credit for the key indicators of political grit and integrity: context and history.

John McCain may espouse the weakest platform of the three, but he adopted his position early and at high potential political cost. Both Clinton, who logged more dinner time with Al Gore then almost anyone, and Obama, a N.Y. PIRG college intern who credits LCV with his surprise victory in his first Senate race, were positioned to be strong climate action advocates but did not do so.

McCain has also shown more grit and leadership by his willingness to challenge the influence of money in politics, also at greater potential cost to a Republican, while Clinton and Obama are neither advocates of political reform, nor have they been notable for bucking special interests.

We must also consider what political conditions we should anticipate. The gathering climate crisis will strain politics-as-usual, just as slavery stressed the pre-Civil War era. The largest fault line runs through the Republican Party, with fossil fuel interests and Neanderthal conservatives on one side, and enlightened business interests and traditional conservatives/conservationists on the other. The Republican Party, like the Whigs, may well collapse, putting more value on installing a Republican in the White House.

Finally, a global solution can only be achieved under vigorous U.S. leadership. We must put up money and make new technologies freely available, but we will also need to bring to bear all the muscle of American superpower diplomacy and military menace. Democrats are congenitally conditioned against any international flexing of U.S. power. We know Republicans don’t have that problem. I’m not urging a McCain endorsement, just pointing out that the case for Obama or Clinton is not clear cut.

Unfortunately, while the times cry out for third party candidacies, the offerings are dismal. Ralph Nader’s recent announcement didn’t mention climate, while the Green Party has descended into internecene warfare between leftist camps with barely a veneer of “green” left between them.

The prudent course of action for environmentalists is to set a high standard — a platform that acknowledges the 350 ppm / 1.0 degrees C limit at a minimum — and be willing to make no endorsement. Failure to do so forfeits our leverage in the Democratic intramural battle and general election, and endorsing any candidate without a significant change in the candidate’s platform would be criminally irresponsible.

Turning to Congress, the same crucial factor of leadership pertains. It is of surpassing importance in this election that we elevate electing a handful of climate action leaders above all other objectives. Our ability to craft effective climate strategy is hamstrung by the lack of political leaders who see themselves as climate advocates operating within the political arena, coordinating with climate campaigners and organizers on the outside.

Two examples of such leaders are Mark Udall, running for U.S. Senate in Colorado, and Mike Brennan, running for U.S. Congress in Maine. Udall is co-chair of the 218-member Renewable Energy and Energy Efficiency Caucus in the House and is author of a number of broad climate bills. Brennan has a history advocating sustainable energy that goes back to 1980, when I worked with him on the Campaign for Safe Energy, winning an anti-nuclear, pro-renewables plank in the Democratic national party platform. Both Udall and Brennan are distinguished by their ability to rise above petty infighting and bureaucratic mindedness with humor and warmth, while keeping their eyes on the prize.