It’s true that scientists don’t know exactly how much world temperatures will rise if we persist with business as usual. But that uncertainty is actually what makes action so urgent. While there’s a chance that we’ll act against global warming only to find that the danger was overstated, there’s also a chance that we’ll fail to act only to find that the results of inaction were catastrophic. Which risk would you rather run?

Martin Weitzman, a Harvard economist who has been driving much of the recent high-level debate, offers some sobering numbers. Surveying a wide range of climate models, he argues that, over all, they suggest about a 5 percent chance that world temperatures will eventually rise by more than 10 degrees Celsius (that is, world temperatures will rise by 18 degrees Fahrenheit). As Mr. Weitzman points out, that’s enough to “effectively destroy planet Earth as we know it.” It’s sheer irresponsibility not to do whatever we can to eliminate that threat.

Now for the bad news: sheer irresponsibility may be a winning political strategy.

Mr. McCain’s claim that opponents of offshore drilling are responsible for high gas prices is ridiculous  and to their credit, major news organizations have pointed this out. Yet Mr. McCain’s gambit seems nonetheless to be working: public support for ending restrictions on drilling has risen sharply, with roughly half of voters saying that increased offshore drilling would reduce gas prices within a year.

Hence my concern: if a completely bogus claim that environmental protection is raising energy prices can get this much political traction, what are the chances of getting serious action against global warming? After all, a cap-and-trade system would in effect be a tax on carbon (though Mr. McCain apparently doesn’t know that), and really would raise energy prices.

The only way we’re going to get action, I’d suggest, is if those who stand in the way of action come to be perceived as not just wrong but immoral. Incidentally, that’s why I was disappointed with Barack Obama’s response to Mr. McCain’s energy posturing  that it was “the same old politics.” Mr. Obama was dismissive when he should have been outraged.

So as I said, I’m very glad to know that Nancy Pelosi is trying to save the planet. I just wish I had more confidence that she’s going to succeed.