I’d love to hear your thoughts on this day.

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The excitement here in D.C. is palpable. We have friends in town who brought their five-year-old and are walking down to the National Mall. My wife got an invitation to watch the whole thing from an office that overlooks the Capitol.

I’m an indoor type (Duh!) — especially on a cold day with a wind chill that could only warm the hearts of anti-scientific global warming deniers. And someone needs to stay home with my 21-month-old daughter and blog.

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She is so excited. She keeps saying “Where is Barack Obama?” and “Is Joe Biden here?” (Note: If you ask her who ran against Barack Obama, she’ll answer “Grumpy old man.” Go figure!)

So what is the great challenge for Obama?

Global warming, obviously, but what does he need to do?

Yes, he needs to pass a major climate bill and accelerate the deployment of cleantech. But those are really secondary challenges.

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No, the single most important thing he needs to do is to change the political equation in this country.

Humanity must stabilize atmospheric concentrations of carbon dioxide at 450 ppm or lower. We must. The risks of failing to do so are simply too grave.

The notion that we can possibly stabilize at 550 ppm or 650 ppm is now I think debunked in the scientific literature because of the growing evidence that those CO2 levels will take us through tipping points in the global carbon cycle that will result in amplifying feedbacks that take us to 800 to 1,000 ppm or higher. In fact, many leading climate scientists think 450 ppm — if sustained for an extended period of time — is enough to take us beyond safe thresholds.

But stabilizing at 450 ppm (let alone below that) is simply not politically possible today. The recent USCAP proposal certainly makes that clear (see “NRDC and EDF endorse the weak, coal-friendly, rip-offset-heavy USCAP climate plan” and NRDC’s reply).

Yet by the end of Obama’s second term, stabilizing at 450 ppm must be politically possible or else it will be all but unattainable. (If Obama is a one-term president, that almost certainly means he has failed and been replaced by a Republican, who, with almost equal certainty, will not aggressively pursue the needed climate action (see “The Deniers are winning, but only with the GOP” and my series on the conservative and stagnation movement — The conservative stagnation, Part 12: Cap-and-trade bill will return GOP to power “in 2010”)).

And that means that not only must Obama change U.S. climate politics, but he must also bring China along with him.

The challenge for Obama and his team is to make the science tangible and the moral necessity self-evident. I suspect he will need some “help” over the next eight years from the increasingly painful reality of human-caused global warming itself. And indeed temperatures are poised to soar — if not in the very short term, then certainly over the next several years.

How Obama can meet this challenge will be the subject of later posts, but it obviously starts with his inaugural address, whose theme will be the central one for meeting all of the challenges that face our nation today — “responsibility.”

This post was created for ClimateProgress.org, a project of the Center for American Progress Action Fund.