Earlier this week, New York's Gov. Andrew Cuomo (D) issued a pointed statement on climate change and its role in the monstrous storm from which his state -- and many others -- will be recovering for months, and perhaps years, to come.
"It's a longer conversation, but I think part of learning from this is the recognition that climate change is a reality," Cuomo said. "Extreme weather is a reality. It is a reality that we are vulnerable."
That's a message many climate scientists have been trying to deliver for a very, very long time. But whether Hurricane Sandy and the hulking, 1,000-mile-wide superstorm she ultimately became will galvanize political opinion, and lead to concrete action, remains very much an open question -- not least because the event is animating a familiar debate: Some stakeholders view the disaster as hard evidence that climate change is upon us, while others argue that such storms might easily come about anyway, as a function of natural variability.
At this stage of scientific understanding -- and some recent research notwithstanding -- it cannot be denied that the latter camp has a fair point. But with millions of Americans still lacking power and tens of thousands cut-off from food, transit, and other basic services in the wake of the savage storm, some climate experts suggest an equally fair retort would be, so what?
"Some critics would like people to believe that because we don't know everything, we know nothing," said Michael Mann, a climatologist and director of the Earth System Science Center at Pennsylvania State University. "That simply isn't true, and these folks do a disservice to the discourse by continuing to go out of their way to feed this misleading narrative."
Indeed, setting aside the millions of fossil fuel lobbying dollars that have polarized Congress on the issue, that narrative, which turns on the myriad things we don't know about the future impacts of global warming -- How hot? How soon? Now? That storm? -- is a distraction of its own, Mann and others suggest. It has also played a key role in keeping serious discussion of climate change off the table, even with a sitting president who is, it would seem, sympathetic to the fundamental science.
As it is, the science suggests that human-driven global warming is creating an environment capable of amplifying the energy of certain storms, by providing warmer ocean temperatures, say, or moister air, and other ingredients that hurricanes need to thrive. Sea levels, too, are now more than 7 inches higher than they were at the dawn of the 20th century -- a phenomenon that most scientists tie directly to climate change. This raises the odds that any storm, whatever its origin, will be able to push the ocean up over sea walls that once seemed adequate, but as Cuomo noted on Tuesday, are no longer commensurate with the threat.
Sliced most delicately, none of this provides unequivocal proof that this storm -- in whole or in part -- can be blamed on humanity's deep and abiding reliance on burning coal, oil and natural gas. Kevin Trenberth, a senior scientist with the National Center for Atmospheric Research in Boulder, Colo., suggests, for example, that mankind's culpability in adding furor to a storm like Sandy might amount to perhaps 5 or 10 percent.
"Most of what's going on, if you turn it around, you'd say 90 to 95 percent is due to natural variability," Trenberth said. "There's a large element of chance on aspects of these things. But when you're already stretching the limits and you're at very high levels of rainfall, if you add a little bit extra on -- especially 10 percent extra on -- that can really break things."
That measure of human influence might seem small to some, but to Trenberth it's the only part of the climate equation that's in any way within our control, and by that measure, it's significant. Parsing what percentage of any particular storm can be tied to human-induced climate change, and what part derived from the random mixing of meteorological factors, he suggested, is a purely academic exercise.
"We've got this new normal. We've got this changed environment, so my view is that everything is affected. If the question is how large this effect actually is, well, it's not 100 percent. So of course you should never say: 'This storm is caused by climate change.' But that's really the wrong approach.
"We have to get past this aspect of saying 'Oh, it might be just natural variability, because these sorts of storms can occur without climate change.' That's not helpful at all," Trenberth said, "and the reason is because the human component is only going to grow over time."
Michael Oppenheimer, a professor of geosciences and international affairs in the Department of Geosciences at Princeton University, echoed Trenberth's assertions. To Oppenheimer, there are certainties involving human safety and vulnerability that a storm like Sandy puts into stark relief, and quibbling over percentages, while interesting, misses a larger point.
"Whether or not there was a climate change component to this storm, it teaches us a lot of things, including how behind the 8-ball we are in being able to handle big events of the type that we believe -- that scientists think -- are going to get more frequent and intense in the future," Oppenheimer said. "So whether this one was 5 percent due to climate change or 1 percent or 10 percent -- it's interesting, it matters to a certain extent, but it's not the whole story by any means."
To Gary Yohe, a professor of economics and environmental studies at Wesleyan University in Connecticut, and a co-chair of the U.S. Global Change Research Program's National Climate Assessment, the whole story is really still unfolding -- and storms like Sandy are just a taste of what's in store.
"First of all, the changes in the current climate that have been observed across the planet are the products of only about 50 percent of the warming to which we have already committed ourselves with our past emissions," Yohe said. "This means that the planet would warm another 2 to 4 degrees Fahrenheit through the middle of this century even if concentrations of heat-trapping gases were to achieve their maximum tomorrow -- not likely, since sustaining a specific concentration starting tomorrow would require an 80 percent reduction in emissions overnight."
Yohe adds that until those atmospheric concentrations of greenhouse gases stop going up, we will not really know a "new normal," because the situation will become increasingly volatile.
"What we have been experiencing recently is only the harbinger of a future that will be punctuated by more severe weather extremes and increasing damage," Yohe said, "all driven by past and future emissions of heat-trapping gases."
The ravages of Sandy may be helping to re-focus political and popular attention to the problem, though whether or not that attention will be sustained after the long clean-up is over is unclear. Jennifer Morgan, the director of the climate and energy program with the World Resources Institute, said she was encouraged to see this week's storm generate a bit of bipartisanship in the form of President Barack Obama and New Jersey's Republican Governor Chris Christie, who have appeared to work particularly well together in tending to the post-hurricane disaster.
Morgan also said that those holding out for more definitive scientific evidence of global warming's impacts are being foolish. "While it's important to understand the scientific evidence underpinning these events, waiting for certainty that a particular storm or other event is caused by climate change is courting disaster," she said. "You don't wait for 100 percent certainty that your house will burn down before you take out fire insurance."
Just what that insurance ought to look like, of course -- beyond building higher sea walls and otherwise adapting to more tumultuous weather -- has been matter of debate for decades now, and it continues to be a key source of paralysis in Washington. Some lawmakers, like Rep. Ed Markey, a Massachusetts Democrat, have long argued for Congressional action that would curb greenhouse gas emissions across the economy as part of a long-term strategy to begin reversing the baseline climatic trends tied to global warming.
"The oceans are hotter, giving added fuel to storms like Sandy," Markey said in an email message. "The seas are rising, especially on the East Coast, allowing storms to do more damage. Storms will always happen, but we know climate change is making them worse," he added. "Car accidents will also happen, but driving drunk or speeding will make them worse."
Critics of broad climate policy, however, suggest that no law or regulation enacted in the U.S. could have an impact on a problem that is now being largely driven by massive greenhouse gas emissions from elsewhere on the planet -- chiefly China, India and other fast-developing economies. "In the year 2000, Chinese emissions were 60 percent below those of the U.S., and by 2010 they had risen to 40 percent above," said Patrick J. Michaels, director of the Center for the Study of Science at the free-market Cato Institute. "If you linearize those projections, their emissions will soon dwarf the whole so-called developed world, so it really doesn't matter, unless you can convince them to stop. Otherwise, policy options are futile."
Michael Mann suggested that there was a moral bankruptcy to this thinking. "Here is the critical point," he said. "We have gained relative to the developing world through two centuries of access to cheap fossil fuel energy. What sort of moral authority do we have in negotiations aimed at convincing them to reduce their own emissions, if we show no willingness to do the same after having had a two century head-start in building a fossil fuel based economy?"
Still, placing broad curbs on emissions through legislation proved a political non-starter in the early part of President Obama's term. The White House has pushed new regulations through the executive branch that aim to raise fuel efficiency standards on cars and limit emissions from coal plants. These moves have been welcomed by activists, though many argue that it is nowhere near enough, given the impacts humans are having on the climate.
Meanwhile, the campaign of Obama's Republican rival, Mitt Romney, has repeatedly made clear, that global warming is a low priority.
That was at least partly behind NYC Mayor Michael Bloomberg's decision on Thursday afternoon to endorse Obama for a second term. "Our climate is changing. And while the increase in extreme weather we have experienced in New York City and around the world may or may not be the result of it, the risk that it might be -- given this week's devastation -- should compel all elected leaders to take immediate action," Bloomberg wrote.
Bloomberg also said: "I want our president to place scientific evidence and risk management above electoral politics."
If nothing else, climate activists say, that scientific evidence -- while perhaps not perfect -- is clear enough.
"Hurricanes start because a tropical wave comes off the African coast and hits the ocean and begins to spin, and it has always been thus," said Bill McKibben, the environmentalist and founder of the climate action group 350.org. "But we live in a world where -- and no one doubts this -- the atmosphere over that ocean is 5 percent moister on average than when I was born. We've done very big things on this earth -- that's the point. It's not the one we were given, it's increasingly one we've made."