Hurricane Sandy and Global Warming

Both the blogosphere and the mainstream media have been abuzz with commentary blaming global warming for Hurricane Sandy and the associated deaths and devastation. Bloomberg BusinessWeek epitomizes this brand of journalism. Its magazine cover proclaims the culpability of global warming as an obvious fact:

Part of the thinking here is simply that certain aspects of the storm (lowest barometric pressure for a winter cyclone in the Northeast) and its consequences (worst flooding of the New York City subway system) are “unprecedented,” so what more proof do we need that our fuelish ways have dangerously loaded the climate dice to produce ever more terrible extremes?

After all, argues Climate Progress blogger Brad Johnston, quoting hockey stick inventor Michael Mann, “climate change is present in every single meteorological event”:

The fact remains that there is 4 percent more water vapor – and associated additional moist energy – available both to power individual storms and to produce intense rainfall from them. Climate change is present in every single meteorological event, in that these events are occurring within a baseline atmospheric environment that has shifted in favor of more intense weather events.

Well sure, climate is average weather over a period of time, so as climate changes, so does the weather. But that tautology tells us nothing about how much — or even how — global warming influences any particular event. Moreover, if “climate change is present in every single meteorological event,” then it is also present in ”good” weather (however defined) as well as “bad.”

Anthony Watts makes this criticism on his indispensable blog, noting that as carbon dioxide (CO2) concentrations have risen, the frequency of hurricanes making landfall in the U.S. has declined.

The US Has Had 285 Hurricane Strikes Since 1850: ‘The U.S. has always been vulnerable to hurricanes. 86% of U.S. hurricane strikes occurred with CO2 below [NASA scientist James] Hansen’s safe level of 350 PPM.’

If there’s anything in this data at all, it looks like CO2 is preventing more US landfalling hurricanes.

Data Source: NOAA; Figure Source: Steve Goddard

Cato Institute climatologists Patrick Michaels and Chip Knappenberger put the point this way:

Global warming has to affect “the weather” in the United States, or anywhere else. Big deal. Changing the radiative properties of the atmosphere — which is what increasing carbon dioxide does — must alter the character of weather events as well as the climate. But how much? In reality, the amount of weather related to natural variability dramatically exceeds what is “added on” by global warming. This is obvious from a look at the “Climate Extremes Index” from the National Climatic Data Center …

Source: National Climate Data Center (Note: The graph above differs slightly from the one presented in Pat and Chip’s column because it incorporates NCDC’s tropical cyclone indicator.)

Michaels and Knappenberger go on to observe:

While it is true that this index has risen from a low point around 1970, it is also clear that it merely returned to values observed in the early 20th century. Did greenhouse gases raise the extremes index in the early 20th century? Obviously not.

Hurricanes are certainly less common in New York than in Florida or Louisiana, but if Sandy’s invasion of the Big Apple is evidence of global warming, then global warming has menaced the Empire State for centuries, because hurricanes have hit New York since before the industrial revolution.

Wikipedia has a List of New York Hurricanes going back to the 17th century. The strongest was the New England Hurricane of 1938, a category 3 storm that killed upwards of 600 people.

As I read the Wiki list, the following number of hurricanes have affected New York: 6 before 1800; 23 from 1800 to 1899; 11 from 1900 to 1949; 15 from 1950 to 1974; 21 from 1975 to 1999; and 19 from 2000 to the present (including Sandy). Each storm in the Wiki list is footnoted, usually with a link to the source referenced.

Lest anyone see a greenhouse “fingerprint” in the larger number of hurricanes since 1975, 16 were “remants” of tropical storms. In contrast, only one “remnant” is identified for 1950-1974 and none is identified for 1900-1949. No doubt New York experienced many hurricane remnants that were not identified as such before the advent of weather satellites and hurricane hunter aircraft.

Okay, but what about Sandy’s record-breaking storm surge — is that evidence global warming added extra oomph to the storm’s destructive power?

Anthony Watts posts an illuminating commentary by David Middleton, who compares Sandy’s estimated maximum storm surge with other hurricane surges in southern New England based on Donnelly et al., 2001. Middleton writes:

Hurricane Sandy’s unprecedented storm surge was likely surpassed in the New England hurricanes of 1635 and 1638. From 1635 through 1954, New England was hit by at least five hurricanes producing greater than 3 m storm surges in New England. Analysis of sediment cores led to the conclusion “that at least seven hurricanes of intensity sufficient to produce storm surge capable of overtopping the barrier beach (>3 m) at Succotash Marsh have made landfall in southern New England in the past 700 yr.” All seven of those storms occurred prior to 1960.

The early 1600s were the depth of the Little Ice Age, the coldest century of the past two millennia and possibly the coldest century since the cooling event of 8,200 years ago.

Anthony also posts a commentary by Caleb Shaw, who argues that the 11.2-foot storm surge from the 1821 Norfolk-Long Island Hurricane would likely have surpassed Sandy’s 13.8-foot surge had the same non-meteorological factors been present:

The people of the time reported a tide 13 feet above the ordinary high tide, but the best studies put the peak tide at 11.2 feet. Sandy reached 13.88 feet. . . .Simple arithmetic suggests the 1821 storm’s high water was 2.68 feet lower than Sandy’s. However the interesting thing about the 1821 storm is that it came barreling through at dead low tide. Tides in New York vary roughly 6 feet between low and high tides.

Therefore, to be fair, it seems you should add six feet to the 1821 storm, if you want to compare that storm with Sandy’s surge at high tide. This would increase the 1821 high water to 17.2 feet.

On top of that, you have to factor in the influence of the full moon during Sandy. That adds an extra foot to the high tide. Add an extra foot to the 1821 score and you have 18.2 feet.

Sandy was a category 1 hurricane before making landfall in the Northeast, which means many landfalling hurricanes, including some previous storms striking New York, had much higher wind speeds. What made Sandy a “superstorm” was the hurricane’s merging with a strong winter storm. MIT climatologist Kerry Emanuel calls Sandy a “hybrid” storm:

Hurricanes and winter storms are powered by completely different energy sources. The hurricane is powered by the evaporation of sea water. Winter storms are powered by horizontal temperature contrasts in the atmosphere. So hybrid storms are able to tap into both energy sources. That’s why they can be so powerful.

NASA scientist Roy Spencer provides a similar explanation:

It is basically the “perfect storm” scenario of the chance timing of a tropical cyclone merging with an extra-tropical winter-type storm. Without Hurricane Sandy off the coast, the strong trough over the eastern U.S. (caused by cold Canadian air plunging southward) would have still led to a nor’easter type storm forming somewhere along the east coast of the U.S. But since Hurricane Sandy just happens to be in the right place at the right time to merge with that cyclone, we are getting a “superstorm”.

This merger of systems makes the whole cyclone larger in geographical extent than it normally would be. And this is what will make the surface pressures so low at the center of the storm.

The immense area of the storm is also what enabled the winds to pile up huge masses of water into the big waves that pummeled the East Coast.

Is there a causal connection between global warming and the formation of hybrid storms? Not enough research has been done on this phenomenon to say one way or the other, Emanuel contends:

We don’t have very good theoretical or modeling guidance on how hybrid storms might be expected to change with climate. So this is a fancy way of saying my profession doesn’t know how hybrid storms will respond to climate [change]. I feel strongly about that. I think that anyone who says we do know that is not giving you a straight answer. We don’t know. Which is not to say that they are not going to be influenced by climate, it’s really to say honestly we don’t know. We haven’t studied them enough. It’s not because we can’t know, it is just that we don’t know.

But surely, the magnitude of the damage wrought by Sandy is evidence something is amiss with the global climate system, right? Actually, no, argues hurricane expert Roger Pielke, Jr. in a Wall Street Journal column.

In studying hurricanes, we can make rough comparisons over time by adjusting past losses to account for inflation and the growth of coastal communities. If Sandy causes $20 billion in damage (in 2012 dollars), it would rank as the 17th most damaging hurricane or tropical storm (out of 242) to hit the U.S. since 1900 — a significant event, but not close to the top 10. The Great Miami Hurricane of 1926 tops the list (according to estimates by the catastrophe-insurance provider ICAT), as it would cause $180 billion in damage if it were to strike today. Hurricane Katrina ranks fourth at $85 billion.

To put things into even starker perspective, consider that from August 1954 through August 1955, the East Coast saw three different storms make landfall — Carol, Hazel and Diane — that in 2012 each would have caused about twice as much damage as Sandy.

With respect to hurricane damages, the chief and as yet only discernible difference between recent and earlier decades is that ”There are more people and more wealth in harm’s way,” in Pielke Jr.’s words. So there is an “anthropogenic” component, but not the sort about which warmists complain. “Partly this [increase in damages] is due to local land-use policies, partly to incentives such as government-subsidized insurance, but mostly to the simple fact that people like being on the coast and near rivers.”

The upshot for policymakers? Since “even under the assumptions of the IPCC changes to energy policies wouldn’t have a discernible impact on future disasters for the better part of a century or more,” the “only strategies that will help us effectively prepare for future disasters are those that have succeeded in the past: strategic land use, structural protection, and effective forecasts, warnings and evacuations. That is the real lesson of Sandy.”

 New York Times environment blogger Andrew Revkin comes to a similar conclusion:

You can have this endless debate about, “Was this storm our fault?”  But the thing I’ve been trying to write on Dot Earth the last few days is that the impacts of this storm are 100 percent our fault. In other words, we make decisions every day as human beings about where to live, what kind of building codes, what kinds of subsidies for coastal insurance, and that’s where there’s no debate about the anthropogenic influence. The fact that the tunnels filled showed that we in New York City, New York State and this country didn’t make it a high priority to gird ourselves against a superstorm.