What Climate Change?
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| Hurricane Sandy is seen on the east coast of the United States in this NASA handout satellite image taken at 0715 GMT, Oct. 29, 2012. |
What can Mother Earth do to be any more obvious?
Sandy truly will be the perfect storm—not just because a hurricane is meeting a northern blockage that will fuel its strength as it hits land as well as another western storm system, but because Sandy is set to strike the richest and most populated part of the U.S. “We’re looking at impact of greater than 50 to 60 million people,” said Louis Uccellini, head of environmental prediction for the National Oceanic and Atmospheric Administration (NOAA). A drone strike couldn’t be better targeted to cause maximum damage than this storm. (Time)
As New York's subways, trains and buses prepared to shut down on Sunday night, and hundreds of thousands of New Yorkers geared up to evacuate the city, close to 100 activists, 350.org supporters and passersby held a banner emblazoned with the words "End Climate Silence," clear enough to be legible from Times Square's surrounding skyscrapers.
In a statement, 350.org president and best-selling author Bill McKibben said meteorologists have called Sandy "the biggest storm ever to hit the U.S. mainland, which is a reminder of how odd our weather has been in this hottest year in American history."
Meteorologists have pointed to warmer ocean temperatures as a key factor in the power and speed of recent storms, including last year's Hurricane Irene. The National Climatic Data Center concluded that September 2012's ocean temperatures were tied with 2005 temperatures for the warmest in history.
And from KERA News:
It was not a good year for people, weather and climate. The winter was strangely warm in many places and the summer ridiculously hot. As a large fraction of the country suffered through extreme or even extraordinary drought many folks naturally wondered, "Is this climate change?" Then along came a presidential election in which the words "climate change" disappeared from the dialogue. Now, just a week or so before voting day, the convergence of westbound Hurricane Sandy with a eastbound cold front is creating a massive storm, a Frankenstorm even, that is threatening millions of Americans. Weird weather is making yet another appearance in our lives and once again we ask, "Is this climate change?"
The hyper-charged political landscape we are crossing now creates its own sparks when trying to answer that question. In a world looking for "wake-up calls" and "smoking guns," how do scientists address the thorny issue of attribution? Did anthropogenic climate cause the storm that rained out your picnic yesterday? Is it causing the terrifying storm crawling up the East Coast now? There are deep, powerful and potent issues here that touch on both science and the relationship between science and politics.
For years, most climate scientists would say it's impossible to link an individual weather event with climate change. That, in fact, is the difference between weather and climate. Climate is all about long-term trends—not the 5-day forecast.
Researchers like Randall Dole of NOAA, for example, might ask what percentage of an extreme event's magnitude came from a changing climate. Peter Stott of the UK Met Office frames the question differently. He looks at the odds for a given extreme weather event to occur given human-driven climate change. Kevin Trenberth of NCAR takes a third view, asking: Given a changed background climate, how should we expect weather to change?
All of these different perspectives (sometimes framed as "Weather on Steroids") have led to new quantitative explorations of climate change's role in what is happening now, not 30 years in the future. In an early example of attribution science Peter Stott and colleagues took on the extraordinary heat waves that struck Europe in 2003 (killing thousands). Their conclusion?
"...we estimate it is very likely (confidence level >90%) that human influence has at least doubled the risk of a heat wave exceeding this threshold magnitude."This kind of science has allowed researchers to get a much better handle on attributing climate change as a game changer for events like this summer's killer heat and drought.
So how about the Frankenstorm?
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. Which brings us to our bottom line. The science of climate attribution is very exciting and full of cool, new ideas. It has already provided us with first steps towards more precision in understanding how climate change is changing climate now, already. For hurricanes, however, sticking to the science means it is still hard to point to an individual storm and say, yes! Climate change! A more reasoned approach is to take the full weight of our understanding about the Earth and its systems and go beyond asking if any particular event is due to global warming or natural variability. As Kevin Ternbeth of NCAR says "Nowadays, there's always an element of both."
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In a Science 2.0 article this morning, Robert Cooper outlines coverage of the storm and how it connects to the climate change debate. A reprint of those concepts is below:
Hurricane Sandy, 2012:
Massive and dangerous Hurricane Sandy has grown to record size as it barrels northeastwards along the North Carolina coast... -Jeff Masters, Weather Underground, Oct. 28 2012.Science paper, 2010:
Fewer but fiercer and more-destructive hurricanes will sweep the Atlantic Basin in the 21st century as climate change continues, a new modeling study by U.S. government researchers suggests. -commentary by Richard Kerr on Bender, M.A. et al., 2010. Science, 327(5964), pp.454–458.Hurricane Sandy, 2012
If ‘Frankenstorm’ pans out to be as powerful and odd as the models currently forecast, then it may be said that this storm will be unique in the annals of American weather history. -Christopher Burt, Weather Underground, Oct. 26, 2012Report by the National Research Council, 2010:
The destructive energy of Atlantic hurricanes is likely to increase in this century as sea surface temperature rises -"America's Climate Choices: Adapting to the Impacts of Climate Change". National Research Council, National Academies of Sciences, 2010Robert Cooper reporting: Where I sit in New Jersey, we are preparing for a direct hit from a record-setting hurricane. We all know that no one event can be blamed on climate change. But this freak storm certainly seems to match the warnings we've gotten over the past decade. There are at least three factors making Hurricane Sandy such a threat: 1) Warm sea surface temperatures, 2) A "blocking pattern" shoving the storm back on shore, 3) A merger with a winter storm.
1) Warmer oceans. Global warming has been raising sea surface temperatures around the world. The water off New England set record highs this year, meaning that Sandy will have more energy to feed from than usual as she churns North.
Sandy will draw energy from the abnormally warm ocean just off the Atlantic coast. Note this is in Celsius. The water off NJ is about 5°F higher than average, and set record highs in 2012. Source: NOAA National Hurricane Center.Yes, there are natural variations that affect sea surface temperatures, in particular the Atlantic Multidecadal Oscillation. But consider the steady climb of North Atlantic temperature changes from normal. The ~60 year oscillation is clear, but so too is the fact that each peak is stronger than the one before.
North Atlantic sea surface temperature anomalies (°C). Source: Wang, C.&Dong, S., 2010. Geophys. Res. Lett, 37, p.L08707.2) Blocking pattern. A blocking pattern is essentially when the jet stream gets kinked. The current kink is pushing Sandy back on shore where most hurricanes would keep veering out to sea. A recent analysis showed that blocking patterns like this are more likely thanks to a warming Arctic. As Arctic sea ice keeps melting to new record lows, the darker water absorbs more heat, which it later releases to the atmosphere. The effect of all this is a weaker jet stream more prone to kinking.
3) Merging with a winter storm.
Prediction: Rising temperatures will give hurricanes warmer oceans to feed from, and more moisture to dump on us, making them more destructive. Observation: we are about to get walloped by what looks to be a history-making storm. Prediction: ocean temperatures will keep rising and blocking patterns will become more frequent. Observation: Hurricane Sandy is feeding off of record ocean temperatures and a kinked jet stream.
Now, it is certainly true that we still don't completely understand hurricanes. It is true that models are not perfect. It is true that Hurricane Sandy could have happened even without climate change. It is true that climate change doesn't "cause" an event, just like doping alone won't win you the Tour de France. And, as always, it is true that we should not draw conclusions from a single event. So then, is Hurricane Sandy just a freak event, or is she an instructive example of what we should expect more often? Let's look at a paper just published in PNAS, which put together a long-term data set of hurricane activity based on storm surges. That means this is not a model – it is empirical evidence from the past 90 years.
We observe that [hurricane activity is greater in] warm years... than cold years and that the relative difference... is greatest for the most extreme events. -Grinsted, A., Moore, J.C.&Jevrejeva, S., 2012. Proceedings of the National Academy of Sciences.
