Manhattan, half-dark after Sandy.

ShutterstockBlackout of lower Manhattan after Sandy.

A year ago, as the curtain was closing on 2011, New York City Mayor Michael Bloomberg stood in front of an audience at the United Nations and declared that it would be cities, not national governments, that would lead the fight against climate change. “As mayors — the great pragmatists of the world’s stage and directly responsible for the well-being of the majority of the world’s people — we don’t have the luxury of simply talking about change but not delivering it,” he said.

2012 would prove Bloomberg right. It would also lay bare just how far we still have to go before cities like New York are prepared for he havoc climate change is wreaking — and how hard urban leaders in the U.S. will have to fight to get help from Washington on this and a whole host of other issues. In the closing days of 2012, we watched Republicans in Congress balk at funding disaster relief after superstorm Sandy barreled into New York, inflicting tens of billions of dollars in damage along the Eastern Seaboard.

In the immortal words of Philip Bump: “Oh my God, some politicians are dicks.”

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To put it all in perspective, here’s an overview of Grist’s cities coverage from 2012 in five acts.

Act 1 Cities step up

Bloomberg’s speech at the U.N. was part of the lead-up to the United Nations Earth Summit, held in Rio de Janeiro, Brazil, in June. The summit marked the 20th anniversary of the original Rio Earth Summit, and for a handful of starry-eyed optimists, it represented a chance for world leaders to make bold commitments to tackling climate change and other problems.

Rio, traffic-choked and deeply divided between rich and poor, offered a glimpse of the challenges the world’s cities will face as they struggle to accommodate another 2 billion people by mid-century. It was no great surprise, then, that while international diplomats dithered, leaders of some of the world’s largest cities stepped up, committing to bump up their battle against climate change by, among other things, reducing methane emissions from garbage. (Methane is a greenhouse gas more than 20 times more powerful than CO2, and can be captured and burned to generate electricity.)

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At a press conference, Bloomberg announced that the C40 Cities Climate Leadership Group — a network of 59 cities, including New York and Los Angeles — had already laid plans to cut 248 million tons of greenhouse gases, the equivalent of taking 44 million cars off the road for a year. By 2030, the group could slash carbon emissions by 1 gigaton. “We’re not arguing with each other about emissions targets,” Bloomberg said. “What we’re doing is going out and making progress.”

Act 2 A green-cities arms race

Meanwhile, back at the ranch, U.S. leaders were far too busy running for office to be bothered with the climate fight. President Obama (You are our only hope, Obi Wan!) hardly mentioned climate change on the campaign trail or in the debates. His rival, Mitt Romney, turned it into a punchline.

On the local level, however, urban leaders were engaged in a sort of arms race for the title of “greenest city in America.” And perhaps they should: Cities are responsible for a whopping 70 percent of the global greenhouse gas emissions, according to a report released earlier this year by the Carbon Disclosure Project. They are also increasingly vulnerable to heat waves, droughts, and flooding.

In Los Angeles, where a UCLA study found this year that climate change will drive up average temperatures by an average of 4 to 5 degrees F by mid-century, Mayor Antonio Villaraigosa has enacted an ambitious climate action plan. In Chicago this month, Mayor Rahm Emanuel unveiled a new blueprint for creating 645 miles of bike lanes by 2020. Philadelphia, meanwhile, is sewing the seeds of a sort of green urban renaissance, replete with a burgeoning urban farming scene and a new bike share program. And there are many examples in between.

Act 3 Women take the helm

Many of the people leading the fight against climate change on the city level are women — a surprising number of them quite young and, dare we say it, smoking hot. Grist’s assistant editor, Darby Minow Smith, has talked to more than a dozen of these women for her series “Knope and change.” (The name is a nod to Lesley Knope, the main character in the TV show Parks and Recreation.)

Philly’s sustainability director, Katherine Gajewski, is leading the effort to bring the city into compliance with the Clean Water Act using “green infrastructure” — read: green roofs, rain gardens, streets with porous pavement, etc., that slow, absorb, and evaporate stormwater before it overwhelms the sewers. In Gary, Ind., sustainability chief Lauren Riga has ramped up the recycling program and helped launch an urban agriculture program in a post-industrial city that has been compared to post-evacuation Chernobyl. Fort Lauderdale’s assistant city manager, Susanne Torriente, is preparing her city for rising sea levels — and for good reason: Depending on what happens on worldwide climate action, 48 percent of South Florida could end up submerged.

“There’s been a lack of progress at international negotiations. We saw it in Rio,” Cynthia Rosenzweig, head of Climate Impacts Group at the NASA Goddard Institute for Space Studies in New York City, told me earlier this year. “There’s a growing realization that cities are the right level of governance to tackle climate change issues.”

Act 4 A violent reality check

Which brings us to Oct. 29, when superstorm Sandy roared up the Eastern Seaboard and slammed into New York City, revealing just how sinister the impacts of climate change are — and how ill-prepared we are to deal with them, even where urban leaders have drawn lines in the sand.

As Grist’s Susie Cagle wrote as New York was still reeling from the blow, “There are multiple factors that came together to whip up Sandy, and no one causal judgment, however attractive, is fair. But given the evidence, it’s likely that no matter how Sandy came in to this world, climate change has helped this storm grow bigger, go faster, and head farther than it might have in earlier times and cooler seas.” And Sandy was undeniably a taste of what is to come as warming and rising seas and a warming atmosphere whip up bigger, more frequent storms.

Five weeks after Sandy hit, with parts of New York still without power and flooded buildings still too dangerous to enter, Bloomberg appeared at a press conference with Al Gore and Michael Brune, executive director of the Sierra Club, to begin laying plans for defending the city from future storms. “We may or may not see another storm like Sandy in our lifetimes, but I don’t think it’s fair to say that we should leave it to our children to prepare for the possibility,” he said.

Act 5 A question for 2013 and beyond

Sandy brought into sharp relief what is at stake with climate change. It also made it clear that cities will not be able to tackle the challenge, or respond to its wrath, alone. And yet, on the national level, politicians continue to ignore the issue or pretend that there is still some debate over whether it is even real. And that, in a nutshell, is the challenge facing American cities today.

In recent decades, the U.S. has turned its back on urban areas, pouring billions into car-centric suburbs while allowing inner cities to crumble. As with climate change, we understand what it will take to assuage many of our cities’ worst problems — joblessness, poverty, crime — and yet we’re content to turn a blind eye, dismiss these as someone else’s problem. Many Republicans go so far as to call any policy that would help cities part of the bogus “war on the suburbs.” Urban sustainability efforts, they say, are a United Nations plot to destroy the American way of life.

In truth, cities are the key to battling the climate conundrum, as Alex Steffen eloquently points out in his new book, Climate Zero, published in Grist last month. The question for Americans — for our national and local leaders, for millennial urbanophiles, and baby boomers who say they want to live in cities again — is whether we’re really ready to commit to making our cities work again. The answer to that question will have huge implications not just for our cities, but for our warming planet as well.