Let's get the jail part out of the way right at the start. Central Cell Block in Washington, D.C., is exactly as much fun as it sounds like. In fact, the entire process of being jailed unfolded more or less as any observer of, say, the 84,000 episodes of Law & Order might imagine.Police arrest protesters of the Keystone XL oil pipeline in front of the White House in Washington, DC. (MANDEL NGAN/AFP/Getty Images)

When we were hauled away from the gates of the White House on the morning of Saturday, August 20th, where 65 of us had been peacefully sitting in for an hour to urge the president to veto the proposed Keystone XL pipeline – a 1,700-mile fuse to the biggest carbon bomb on the continent – we were taken, hands cuffed behind our backs, in paddy wagons to the Park Police headquarters across the river Anacostia. There we sat – hands still cuffed – on a lawn for a couple of hours, until one by one we were called inside, uncuffed and stripped of all but our clothes. (I mean all – they took away my wedding ring, which hadn't been off in 23 years, saying, "Where you're going, they'll cut off your finger for that.") An officer with a ballpoint pen filled out every form in triplicate. (The Park Police still seem to be deciding if the whole digital thing is going to work out – there were three IBM Wheelwriter typewriters circa 1974 on a desk, but Bic apparently remains the technology of choice.) We stood 15 men to a five-by-seven cell for five or six hours (until need finally overcame squeamish reticence and we used the toilet in the center of the cell). Eventually, they recuffed us and put us back in the wagon for the ride to Central Cell Block, still with no idea of our prospects.

There the District police fingerprinted us and locked us up, two apiece, in four-by-seven cells. No beds, just two stainless-steel slabs without mattress, sheet or pillow. (Shoes make decent pillows, but it's harder than it sounds to sleep on bare steel – my hips were still bruised two weeks later.) We stayed there all night, all the next day and all the next night; baloney sandwiches and a Styrofoam cup of water arrived at 3 a.m. and 3 p.m. The lights never went off, the din was constant and the heat stifling. (We counted ourselves lucky, however, when we found out that the 20 women under arrest had been left in a single cell without beds of any kind, huddled together to keep warm as guards blasted an air conditioner at them.) The hours passed with incredible slowness, especially since the guards, who had taken our watches, kept lying about the time. But on Monday morning at 5 a.m. (we walked past a clock), they shackled us again, this time by the feet – you really do have to put your hand on the next guy's shoulder, and shuffle down the hall, just like in the movies – and took us to the holding cell at the courthouse, where the 45 of us stood, feet cuffed together, in a giant cage with the rest of the District's weekend criminals for about 10 hours. No food, no water – until finally, all of a sudden, they simply called us out and let us go. The judge, apparently, had dismissed all charges, and we were free.

So – a tough weekend, but no need for sympathy. (If you have some, spare it for those neighborhoods whose citizens are routinely hauled away to jail for no good reason.) Instead, there's a need to understand. Why were 65 middle-class Americans willing to spend that weekend behind bars? And why were 1,200 others willing to follow us into the paddy wagon over the last week of August and the first of September? This was the largest civil disobedience in this country since at least the nuclear-test protests of the 1980s, and one of the most sustained since the heyday of the civil rights movement, and virtually none of the arrestees were the usual suspects. Plenty of college students showed up, but we'd tried hardest to recruit their elders, arguing that in the fight against global warming it was time for the generation that actually caused the crisis to do a bit of the work. The biggest group arrested, in fact, were born in the Truman and FDR years; on the last day, I watched the police haul away an 86-year-old man with a sign around his neck that said "World War II Vet, Handle With Care." He'd been born in the Harding administration.

We were there for a simple reason: because it was time. After two decades of scientists gravely explaining to politicians that global warming is by far the biggest crisis our planet has ever faced, and politicians nodding politely (or, in the case of the Tea Party, shaking their heads in disbelief), it was time to actually do something about it that went beyond reading books, attending lectures, lobbying congressmen or writing letters to the editor. With Texas on fire and Vermont drowning under record rainfall, it wasn't just our bodies on the line.

The Keystone XL pipeline wraps up every kind of environmental devastation in one 1,700-mile-long disaster. At its source, in the tar sands of Alberta, the mining of this oil-rich bitumen has already destroyed vast swaths of boreal forest and native land – think mountaintop removal, but without the mountain. The biggest machines on earth scrape away the woods and dig down to the oily sand beneath – so far they've only got three percent of the oil, but they've already moved more soil than the Great Wall of China, the Suez Canal, the Aswan Dam and the Pyramid of Cheops combined. The new pipeline – the biggest hose into this reservoir – will increase the rate of extraction, and it will carry that oily sand over some of the most sensitive land on the continent, including the Ogallala aquifer, source of freshwater for the plains. A much smaller precursor pipeline spilled 14 times in the past year.

Even if the oil manages to get safely to the refineries in Texas, it will take a series of local problems and turn them into a planetary one. Because those tar sands are the second-biggest pool of carbon on earth, after the oil fields of Saudi Arabia. Burning up Saudi Arabia is the biggest reason the Earth's temperature has already risen one degree from pre-industrial levels, that epic flood and drought have become ubiquitous, and that the Arctic is melting away. Since we didn't know about climate change when we started in on Saudi Arabia, you can't really blame anyone. But if we do it a second time in Canada, we deserve what we get.

If you do the calculations, explains James Hansen – the planet's most important climate scientist, who was arrested at the White House about halfway through the two weeks of protest – opening up the tar sands to heavy exploitation would mean "it's essentially game over" for the climate. Which is a sentence worth reading twice. Right now, the atmosphere holds 392 parts per million CO2, already dangerously above the 350 ppm scientists say is the maximum safe level. If you could somehow burn all the tar sands at once, which thank heaven you can't, the atmospheric concentration would rise another 150 parts per million.

The arguments for going ahead and doing it anyway are predictable, and predictably weak. The Chamber of Commerce claims the pipeline will be a jobs bonanza, but a State Department analysis predicts 6,000 jobs at best, almost all of them temporary, and at the price of further delaying the transition to a truly jobs-rich economy founded on clean energy. Because the pipeline runs to the Gulf of Mexico, the oil won't enhance energy security – much of it is apparently destined for overseas. And it's likely to raise, not lower, the price of gasoline, by opening up more markets for Canadian oil.

All of which means it's going to be one interesting political battle. Because the pipeline crosses an international border, it requires a presidential "certificate of national interest." In other words, Barack Obama alone will decide, without Congress or anyone else in the way. That means the sides have lined up with all the firepower they can muster. And they are different kinds of firepower. The heavy artillery backing Keystone includes the Chamber of Commerce, the Koch brothers and The Wall Street Journal. They're lobbying hard: TransCanada Corp., which will build the pipeline, spent $160,000 lobbying Congress in 2008, $720,000 last year and $790,000 in the first half of this year. They've wired things the traditional Washington way, hiring Hillary Clinton's former deputy campaign manager as their chief lobbyist. Not, perhaps, because of his expertise on pipelines.

And the opponents? Native peoples opened up the fight years ago, and still lead it – they were the first to experience the damage, and they found support from some of the big green groups as the pipeline plan began to unfold. Landowners from the high plains organized along the pipeline route; they did so well in swaying public opinion that both the Republican governor and senator from Nebraska have called on Obama to block the pipe. The dramatic civil disobedience over the summer transformed the fight from a regional into a national and emotional one – 1,253 people got arrested and 612,000 signed petitions. The head of the NAACP, Ben Jealous, showed up to address the demonstrators, and the Hip Hop Caucus helped headline its closing rally. A few days later, nine Nobel Peace Prize laureates – from the Dalai Lama to Archbishop Desmond Tutu – sent a powerful appeal to the president. The New York Times and Robert Redford have also sided with the growing opposition.

Only one guy has not tipped his hand – Barack Obama. His people say he'll decide by year's end. The question is: What will sway him most?

If it's money, it's clear who wins. Because the guys supporting this thing have most of the money on earth – the oil industry is the most profitable thing human beings have ever done, by far. ExxonMobil made more money last year than any company in the history of . . . money. If it comes down to money, and it usually does, we'll lose. That was made perfectly clear in early September, when the president, acting at the behest of the Chamber of Commerce, announced he was blocking new clean-air regulations. These are the kind of laws every president approves – even George W. Bush wanted a stricter standard than we have now. But after the Supreme Court decision in Citizens United, which allows companies to spend whatever they want on political campaigns, the president's men are so scared of the oil industry's big campaign war chest that they've gotten into the habit of obedience.

So far, the oil companies have spent their money well. They've run a huge PR campaign arguing that because, as everyone knows, Muslims are terrorists, then Canadian oil is "ethical oil." (When I debated an industry spokesman on the BBC, he explained that Canadian oil is the equivalent of fair-trade coffee and free-range chicken.) Their willingness to exaggerate seems to know no bounds: Thomas Donohue, the head of the Chamber of Commerce, recently lofted the absurd claim that the pipeline would create work for 250,000 people.

To defeat the big money behind the pipeline, we needed to rely on a different currency, one that we possess and they don't. For two weeks, that currency was our bodies, and we spent them well enough to focus national attention on the pipeline. Even international attention – protesters turned out at embassies on every continent; in New Zealand, a band of 35 opponents managed to shut the Canadian Consulate for the afternoon simply by appearing with an oil-soaked Canadian flag. We made reasonable waves in the American press, reaching the top of Google News by our final day; in Canada, we were a certified Big Story, sparking a conversation that will continue with another wave of civil disobedience planned for Ottawa, where the ruling conservative party is firmly behind the pipeline. By protest's end, the political world was well aware that this had become Obama's central environmental test between now and next year's election. The odds are still against us, but they're better than they were.

And so the next phase of this campaign unfolds. Groups like Rising Tide are blockading trucks hauling heavy equipment to the tar sands; others geared up for the State Department hearings that were held across the country in late September. But mostly we're targeting Barack Obama, because he's the sole decision-maker. Union workers and environmental activists have already begun visiting his campaign offices in cities across the country, telling his staff, politely but firmly, that the pipeline is a vital issue. As the president travels beyond Washington – to an American Legion convention in Minneapolis, to a university in Virginia – he's been finding banners and crowds reminding him of the issue. It's not quite a threat – more like a promise. When Obama's campaign manager, Jim Messina, showed up at Harvard to give a speech, he took one look at the 40 protesters out front chanting, "Obama can stop the tar sands – Yes He Can!" and ducked through a side door.

We're going to target Obama – but we're not going to do him the favor of attacking him. We're not going to say, "We'll never vote for you, you're a corrupt sellout." That's what his aides would like us to do, to marginalize ourselves as the kind of fringe it's politically profitable to defy. Instead, we're going to pay the president the very dangerous compliment of taking his words from the last campaign seriously, and asking him to live up to them.

What words? How about: "At the dawn of the 21st century, the country that faced down the tyranny of fascism and communism is now called to challenge the tyranny of oil."

Or maybe: "Let's be the generation that finally frees America from the tyranny of oil."

Or maybe: "Because if we are willing to work for it, and fight for it, and believe in it, then I am absolutely certain that generations from now, we will be able to look back and tell our children . . . this was the moment when the rise of the oceans began to slow and our planet began to heal."

I remember when he uttered those last words, on the night he clinched the Democratic nomination in June 2008. I remember the chill that ran down my spine. I remember the days I spent standing on New Hampshire snowbanks with Obama signs and driving back roads of the state, searching out rural addresses to urge people to vote. (After I was arrested at the White House, the guy in the jail cell next to me said, "The last time I was this uncomfortable, I was sleeping in a church basement to canvass for Obama.") This is why he won – because he inspired the hell out of us.

Everyone knows that Congress has made his life hard; I'd get tired of dealing with a pack of crazies who have substituted ideology for physics and chemistry. We all cut him slack because of it. But when Congress isn't in the way? When it's just Obama making the call? This is a 20-foot jump shot, top of the key. Take it, for God's sake.

To help nerve Obama up, we'll keep turning people out, by the thousands. On November 6th, exactly one year before the next election, we plan to encircle the White House with protesters, something I'm not sure has ever been done. We won't be getting arrested; instead, it will be like a human Rorschach blot. It's either a giant "O" of hope that he'll do the right thing, or a symbolic house arrest. Many of us will be there in the suits and ties or dresses we wore to get arrested. It's our way of saying: We're not the radicals here. The real radicals run Exxon – they're the people who are willing to alter the chemical composition of the atmosphere. (Abbie Hoffman freaked out an entire nation by threatening to dump LSD in a single reservoir – what a small-time thinker he was!) In any reasonable sense of the word, we're conservatives, hoping to preserve something of the world we were born into.

Many of us will also be wearing our Obama '08 pins. But we'll be taking them off, and leaving them in self-addressed, stamped envelopes at the front of the White House, with a note saying: Send this back once you've kept your word. Choose the side you said you were on when you campaigned so beautifully. We see the hideous drought in Texas, the horrible flooding in Vermont, the steadily acidifying ocean – we see the stakes. We understand what kind of world is coming at us unless you decide to lead. And we still want you to do the right thing. Our message will be: Until you absolutely make us, we refuse to be cynics. But we're not patsies, either.

Because it really is time. Last year was the warmest on record. This year, before August was over, Americans had endured more billion-dollar weather disasters than we've ever experienced in an entire year. The Texas Forest Service, confronting the blazes that destroyed more than 1 million acres over the summer, observes that "no one on the face of this earth has ever fought fires in these extreme conditions." If we ever plan to do something more than talk about the biggest crisis the planet has ever faced, now is the moment to say, "We're going no further down this path." Shutting down Keystone has become the unlikely Lexington and Concord of the climate movement. Revolutions have to start someplace.