The Bush administration is often accused of ignoring science, or, more accurately, waging war on it, and chief among the charges is its response — or lack thereof — to climate change.

The outcry has been tremendous. We’ve seen lamentations from environmentalists, a really expensive Powerpoint — sorry, Mac-heads, Keynote — lecture by Al Gore, a movie narrated by Leonardo DiCaprio, numerous books and lengthy articles in the New York Review of Books, and some Oscar night warbling by Melissa Ethridge. Yet somehow, Bush has remained unmoved and largely indifferent to the issue.

It’s true he’s made token measures, funding alternative energy research, talking up nuclear power, pushed for higher fuel economy standards, and advocated farm-state friendly boondoggles like ethanol. Yet to the primary goal of most global warming activists — mandatory reductions in carbon emissions — he’s basically responded with a yawn. (No doubt some small portion of recent warming can be attributed to environmentalist rages over Bush’s global warming apathy.)

But as of yesterday, Bush has made responding to global warming, if not priority number one, at least something to think about during moments between chats with the Pope and retirement planning. In an afternoon speech at the White House, Bush didn’t go so far as to announce that he’d be amenable to mandatory emissions caps, but he did ask for all emissions growth to cease by 2025 under pressure from “market-based regulations” (a hilariously convoluted coinage; right up there with “peace-based war”).

So Bush is finally taking science seriously, right? Probably not. Then why take this route when he could simply let the issue ride? All the possible answers to that question have nothing to do with science. Instead, Bush’s decision are best explained by some combination of history, legacy, opportunity, and bureaucracy.

THE MOST OBVIOUS reason why Bush made yesterday’s speech is that he’s looking for a legacy. On domestic policy, his accomplishments are few. Although a speech like this doesn’t provide everything the folks at the Sierra Club want (nor even close, really), it does inch toward their position, making Bush look more moderate to average voters paying only mild attention to the news.

Moreover, when climate change legislation really gets going during the next administration, as it likely will — all three remaining contenders support strict emissions limits — Bush will be able to take credit for getting the ball rolling. And even if the speech fails to generate a larger legacy, it will certainly get Bush some immediate attention, something he’s received far less of recently with the ongoing presidential campaigns. Even lame ducks like to quack in the limelight.

Attention, however, might not be all that’s driving the issue. Bush’s shift on climate policy could also be a matter of simple democratic and bureaucratic pragmatism. Rather than have the courts and regulators decide on climate policy, often based on decades old rules, the shift may have been primarily about putting policy back in the hands of elected officials.

In the speech, Bush said that he wanted to avoid seeing climate regulation become a mess. So in a way, it’s a non-stance stance, one that prizes process over principle, and doesn’t care what the result are so long as they’re tidy.

Punting to Congress may sound good in theory, but the problem is that it gives the impression that the bigwigs in the Capitol ought to do something. That’s always a dangerous thing, especially in a Democratically controlled Congress likely to take any instruction to act as license to push the country toward carbon cold-turkey.

FINALLY, BUSH AND his advisers may believe they’re doing conservatives who oppose emissions caps a favor — whether they know it or not. How would this work? Well, by pushing for less stringent regulation than his successors, he might stave off harsher restrictions.

That’s the theory, anyway. The problem with it is that in politics, this approach rarely works. Now that Bush has broached, however so delicately, the subject of flat-lining carbon emissions by regulatory fiat, there’s no going back. Bush’s comparatively modest goal of stopping emissions growth by 2025 could easily expand into Barack Obama’s stated (and borderline ludicrous) goal of reducing emissions by 80 percent in 2050.

Looking that far into the future is about as useful as looking for a golf ball on another continent. Global warming science has progressed far enough that it’s entirely reasonable to assert than human activity is responsible for much of climate change. But while we’ve figured out a significant amount about global warming’s past, its future is still murky. So climate change doomsayers are almost certainly exaggerating when they claim that catastrophe is inevitable without concerted action. The best response to questions about climate change’s effects is to remain gnomic and inscrutable, like a Web 2.0 consultant at a sales meeting.

If the science of the global warming is still fuzzy, the economics of cutting carbon are far less so. Scientists and economists have argued that the phenomenally expensive (some estimates have put it in the hundreds of billions of dollars) Kyoto protocol would have done little to impede climate change. A CBO report last year estimated that the poorest 20 percent of Americans would lose the largest percentage of their income, and that “most of the cost of meeting a cap on CO2 emissions would be borne by consumers, who would face persistently higher prices for products such as electricity and gasoline.”

Meanwhile, previous Bush experiments in regulating energy markets have proven foolhardy. Ethanol and biofuel subsidies in the U.S. and around the world have resulted in more farm land devoted to biofuels, and less for food, causing third world food shortages and even riots.

If there’s one thing that both global warming activists and critics of energy restriction can agree on, it’s that evidence has never much influenced the Bush administration’s climate change policy. Yesterday’s speech had nothing to do with science, nothing to do with economics, and everything to do with politics.