After a campaign season in which it was the missing in action issue, climate change roared back into relevancy in the wake of Hurricane Sandy. Bill McKibben, the writer-turned-activist behind 350.org, put it in stark terms. “This is an absolutely unprecedented storm,” he told POLITICO on Monday evening. “This entire year should be a seriously wake-up call—and the public’s beginning to get it.”
Some scientists and science writers, however, were just as quick to caution that we can’t really attribute any single weather event to climate change—and that tropical cyclones like Sandy have proved particularly hard to connect to global warming. Andrew Revkin of Dot Earth drew a clear line against attributing Sandy directly to recent man-made warming, noting that there had been periods in the past when strong hurricanes occurred during cooler years:
There remains far too much natural variability in the frequency and potency of rare and powerful storms — on time scales from decades to centuries – to go beyond pointing to this event being consistent with what’s projected on a human-heated planet.
Of course, we’ll be grappling with the effects of Sandy—which has already killed over 20 people in the U.S. and which could easily top $20 billion in damages—whether or not it has to do with climate change. But the argument over attribution alone misses the point. We know that climate change is real, that it’s happening and that it will make many natural disasters more severe, from coastal flooding to droughts to storms. But the real danger stems from the fact that we’re putting more and more people and property in harm’s way, in built-up coastal cities like New York or Miami or Shanghai. Along with cutting carbon emissions to reduce the risk from climate change, we need to build and maintain a society that is capable that will prove more resilient to extreme weather in the future.
It’s true that Hurricane Sandy got an unusual boost from extremely warm waters off the East Coast—through the first half of 2012, sea temperatures from Maine to North Carolina were the highest on record. (Some of that warm water may be due to natural variability, however, rather than man-made climate change.) Warmer ocean waters provide more power for tropical cyclones, which is why hurricanes are more common in the tropics and why the Atlantic hurricane season runs roughly over the summer and early fall. A paper published earlier this month in the Proceedings of the National Academy of Sciences made the case that warm years over the past several decades have been more active for cyclones than cooler years. Warmer air—and we’re on track to have the hottest year on record globally—can hold more moisture, which means storms can drop more rainfall. That’s one clear reason why many—but not all—atmospheric scientists believe global warming is likely to help cause stronger storms.
But the possible effect of warming on hurricanes is one of the less perfectly understood aspects of climate science, and there’s still a lot of natural variability at work that makes it difficult to fingerprint the human influence of a major storm. The last Intergovernmental Panel on Climate Change (IPCC) report noted that scientists have “low confidence” in long-term increases in tropical cyclone activity due to man-made warming, and other studies have found evidence of massive storms that hit the Northeast thousands of years ago—well before humans began changing the climate. Sandy was also a truly freak event. The storm likely would have spun harmlessly out to the sea—as many late-season hurricanes do before they strike the East Coast—had it not met a blocking high pressure system that steered it towards the Northeast. That’s some seriously bad luck.
Over at the Houston Chronicle, science reporter Eric Berger noted the challenge of tying Sandy specifically to climate change:
The bottom line is that climate change is unquestionably having an effect on the weather around us by raising the average temperature of the planet. This is producing warmer temperatures and very likely increasing the magnitude of droughts. However, it is a big stretch to go from there to blaming Sandy on climate change. It’s a stretch that is just not supported by science at this time.
When it comes to policy responses, though, it doesn’t really matter exactly what role man-made climate change plays in amplifying storms. For one thing, we know that global sea level rise is happening, and we know that’s large due to man-made warming. And sea level in the Northeast seems to be rising three to four times faster than they are globally, which puts cities like New York—which has more than 580 miles of coastline—at enhanced risk. Storm surges and coastal flooding, rather than high-speed winds or drenching rain, proved to be Sandy’s real bane, with more than 12 ft. of flood water filling New York’s Battery Tunnel. Every subway tunnel beneath New York’s East River was flooded, leaving the system “devastated,” in the words of Metropolitan Transit Authority chairman Joseph Lhota.
As atmospheric scientists Kevin Trenberth told Slate, sea-level rise poses a long-term threat to the world’s coastal cities—a threat that is felt when a storm hits:
Sea level-rise happens episodically. One minute it looks benign and then a week later suddenly a storm or hurricane comes along like Sandy, and there are major waves, 20-foot waves, and major storm surge, and tremendous damage occurs.
Even if the storm just happened to do exactly the same things it’s doing anyway, the fact that sea level went up 6 inches last century, and that sea level is somewhat higher now than it has been at any time in recent history, means that all of the coastal regions are experiencing new levels of pounding and erosion.
Add the fact that coastal areas are becoming more densely populated—putting more people and property in harm’s way—and you have a recipe for a very expensive and dangerous disaster every time a storm like Sandy makes landfall. Climate change is just one more factor contributing to the growing danger from extreme weather. That’s why we need to build societies—and infrastructure—that can be resilient in the face of a natural disaster, or an unnatural one. Limiting the effects climate change through the reduction of carbon emissions and adaptation to extreme weather has to be built into any future development—something Andrew Revkin pointed out in his post yesterday.
We don’t demand absolute certainty before we take action in foreign policy, the economy or health. We’d be fools to wait until there’s perfect scientific consensus on the role that global warming may be playing in tropical storms before we take action to prepare for both. “Anyone who says there’s hasn’t been a dramatic change in weather patterns has been denying reality,” New York Governor Andrew Cuomo told reporters today. “We need to make sure that if there is weather like this we are more prepared and protected than we have been before.” As 8 million struggle without power in Sandy’s wake, that much should be painfully obvious.