/ Maggie Koerth-Baker / 10 am Mon, Oct 29 2012
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  • Did climate change cause Hurricane Sandy? The answer depends on why you're asking

    Did climate change cause Hurricane Sandy? The answer depends on why you're asking

    There are two answers here: One for the legitimately curious, and one for people who want a disaster to be a referendum on climate change.

    Image: Oct. 28, NASA/NOAA polar orbiting satellite. Detail above, full below.

    Last year, I wrote a piece for BoingBoing about destructive storm systems and why it's so difficult to say, in concise sound-bite form, what relationship that destruction has to climate change. In that case, we were talking about tornadoes. But over the last couple of days, lots of people have been having roughly the same conversations about Hurricane Sandy. When the clouds have passed and everybody is done sleeping in airports, people are going to want answers. Was this an unavoidable act of nature? Or was this something caused directly by changes to Earth's climate that have happened because we burn fossil fuels which increase the concentration of carbon dioxide in the atmosphere?

    Again, there's not an easy answer. And, again, part of the problem here is that we're expecting science to operate on the scale of American media news cycles, which doesn't really work. We want to talk about this while the storm is raging or, barring that, at least immediately afterwards. But scientists aren't really going to have anything particularly deep to say about this specific storm for months, if not years. During that time, data will be analyzed and compared, and other events will happen, and that's really the stuff that we need in order to say much of anything other than, "We don't know for certain." In some ways, expecting anything else means forcing scientists to speculate and extrapolate in ways they aren't usually comfortable with and that aren't a terribly great way to understand the big picture.

    But there's also something new, that I kind of didn't really think about when I was writing that post on the tornadoes. The answer to these questions also really depends on the motivations behind why you asked, and what it is that you really want to know.

    First off, you should know that this kind of extreme (and extremely weird) storm system happening in fall or winter is a trend that some scientists had already been predicting. Those predictions stem from the steep reduction in quantities of sea ice in the North Atlantic and what we know (and think we know) about how that change affects climate patterns and storm formation as a whole.

    Remember the times that we've talked about how climate change can, seemingly paradoxically, lead to heavier snowfall in winter? This is connected to that. Here's how Kate Spinner with The Herald Tribune explained it:

    A big bubble of high pressure, with sinking air that moves clockwise, is interrupting the typical steering patterns in the atmosphere. That high pressure creates a blockage, backing up the jet stream so that it bends south, eventually looping north again, instead of flowing toward the east as usual.

    The blocking pattern, centered just south of Greenland, will significantly slow the eastward-moving cold front once it reaches the coast. And it will steer Sandy into the U.S. rather than allowing it to turn east.

    Blocking events are the force behind a lot of crazy weather anomalies, not just hurricanes. And there's evidence suggesting that, as the ice in the Arctic melts, the frequency and/or intensity of the blocking events may be increasing. The Climate Crocks blog did a nice interview about this a few months ago with Jennifer Francis, who studies marine and coastal sciences at Rutgers.

    There's more on this from Francis, and other scientists, at Andy Revkin's DotEarth blog.

    Another thing worth taking into account: Weather is a lot more complicated than you think it is. If it rains today — or if it doesn't rain — there are lots of different, interacting factors that influenced that outcome. A good way to think about it is like a plane crash. It is very, very rare for a plane crash to be caused by a single mistake. Instead, when you're reading the final report, you find that lots of things have to go wrong all at the same time. Even then, you still might not get an accident if the mix of mistakes that happen don't interact with each other in such a way as to make them all worse than the sum of their parts.

    Plane crashes are complicated. And so is weather. That matters, because it means that Hurricane Sandy could be both a completely natural occurrence and a product of climate change. Simultaneously. Some of the factors that caused this storm might be nature-made. Others might be man-made. And teasing apart which factors were responsible for which aspect of the storm's damage is incredibly hard.

    Greg Laden, an anthropologist who does some very good blogging on climate science, had a lot to say on this topic — particularly, the fact that even though we can't say "Hurricane Sandy was caused solely by climate change", we can say that climate change is probably affecting several factors that probably influence the development, growth, and movement of hurricanes.

    It is often said that storms are going to happen anyway, but global warming ramps up the probability, which is akin to saying that there is always going to be variation in temperature or some other weather related factor but global warming raises the baseline. That’s true. But the corollary to that is NOT that you can’t link climate change to a given storm. All storms are weather, all weather is the immediate manifestation of climate, climate change is about climate. Before we started talking about global warming, storms were caused by … things. Climate things. Did we ever say, back in the 1950s when a hurricane hit Florida, “Oh, ya, that was some hurricane, but the thing is, you can’t really attribute a given hurricane to the Intertropical Convergence Zone’s relationship to warm Mid Atlantic currents. The former is a weather event and the latter is a climate system.” Why did we not ever say that? Because it would have been irrelevant, even dumb.

    The truth is, we experience more Atlantic severe storms because of global warming, though we are still working out the details of which features of which kinds of storms are affected most. Beyond this, it may well also be possible that something I hinted at above is true: We may be experiencing kinds of storms today that were very rare in recent centuries, because of global warming.

    Adam Frank at NPR also wrote a good post on this subject. In it, he explains another issue that muddies the waters. When we say that weather is complicated and that a storm is caused by the interaction of lots of different factors, what we are really saying is that weather is a system. Just like climate is a system. Currently, there are some systems that science understands better than others. Hurricanes are, unfortunately, pretty far down on the list.

    There is a hierarchy of weather events which scientists feel they understand well enough for establishing climate change links. Global temperature rises and extreme heat rank high on that list, but Hurricanes rank low. As the IPCC special report on extreme events put it "There is low confidence in any observed long-term (i.e., 40 years or more) increases in tropical cyclone activity (i.e., intensity, frequency, duration), after accounting for past changes in observing capabilities."

    The reasons for "low confidence" are manifold. Some part of the caution comes from the complexity of the problem, and some part comes from the lack of good data before the satellite era (about 1970). Thus, many climate scientists will not want to go out on a limb for hurricanes. They just don't have the tools to make strong inferences.

    This is not to say progress isn't being made. One thing that does seem clear is that warmer oceans (a la global warming) mean more evaporation, and that likely leads to storms with more and more dangerous rainfall of the kind we saw with Hurricane Irene last year. In addition, a paper published just last month, used records of storm surges going back to 1923 as a measure of hurricane activity. A strong correlation between warm years and strong hurricanes was seen. Thus if you warm the planet, you can expect more dangerous storms.

    Basically, we know that the effects of climate change probably has an impact on factors that cause massively destructive storms — even if we don't know exactly how much of an impact; even if we can't really use that information to exactly predict what's going to happen with massive storms in the future; and even if we can't tell you whether Sandy, specifically, was caused by climate change.

    So, really, the answer to the question, "What is the relationship between Hurricane Sandy and climate change", depends primarily on why you're asking the question.

    If you're just kind of curious and/or looking for something to blame, we don't have great answers on that yet. I'm sorry. Nobody is really going to be able to tell you one way or the other.

    But if you're using that question as a proxy to really ask, "Is climate change real and do I have to care about it?", well, good news! We have enough information to answer your question. And the answer is, emphatically, yes.

    Read More:
    Besides the links I included in the story, I want to point you towards a couple more Hurricane Sandy-related things:
    NOAA's Storm Central has all the maps, satellite images, and projections of Sandy that a concerned citizen (or giant nerd) could want
    • The director of the National Center for Disaster Preparedness would like you to know that we are seriously, seriously NOT prepared for big disasters
    Atlantic City is totally flooded
    • Marketplace Tech Report has a really fascinating piece on the future of weather forecasting
    • If you're in Sandy's path and aren't really clear what to do with your pets, read this
    • The NASA Satellite video will haunt your nightmares
    • Meanwhile, the news that the satellites we rely on for forecasts of hurricanes are aging rapidly (and there aren't great plans to replace them) will create your nightmares
    Use this handy slider to compare Hurricane Irene and Hurricane Sandy

    Special thanks to the following people: Bryan Walsh, Ed Yong, CBS Smart Planet, Andrew Thaler, Katherine Hayhoe, James Greyson, Lisa Fleisher, John Matson, and Jennifer Viegas.

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