The Climate in Emergency

A weekly blog on science, news, and ideas related to climate change

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When the Sky Does Not Make Sense

As I explained on Tuesday, the East Coast of the US has been pummeled recently by horrible weather. The worse of the flooding struck South Carolina, but the storm caused flooding every state from Georgia north to Maine and inland as far as Ohio. The storm was remarkable for many reasons, not least because of its vast size and the shear amount of water that fell out of it:

  • In Maine, Caribou, Millinocket, Houlton, and Portland all broke daily rainfall records–Portland’s new record is double the previous record, which was set in 1922. One area, Searsport, received more than ten inches in total from the storm.
  • In Massachusetts, Boston almost doubled its daily rainfall record, previously set in 1899. The worst of the rain had not get moved through the state at that point.
  • In Rhode Island, Provincetown set a new daily record and New Bedford had to shut down Route 18 for two hours due to flooding.
  • Some parts of South Carolina got one or two feet of water out of the storm in total. Dams breached, highways flooded, and caskets literally floated up and out of their graves.

Coastal flooding–a storm surge driven by wind–was just as bad and, in some areas, worse. Just as unprecedented as the flooding was the storm’s structure–record-breaking floods in this part of the world are categorically hurricanes or tropical storms, but this was neither. There is simply nothing in the record-books remotely comparable.

There was a hurricane involved, though.

Hurricane Joaquin was an extremely strong Category 4 storm–its strongest sustained winds were just 2 mph shy of qualifying as a Cat 5. Hurricanes of this intensity are extremely rare–the last one in the Atlantic was five years ago. It hammered the Bahamas and sank a cargo ship with all hands. It never made landfall in the US, but its influence sent high surf along the length of the Eastern Seaboard (in Maine I heard surf about a mile inland–and the closest water is a protected cove that typically has no waves) and contributed to the huge storm surge in the South. The hurricane and the un-named storm were close enough to influence each other, with the monster un-named stormed steering Joaquin and the hurricane funneling moisture into its extratropical partner. This relationship between two storms was also highly unusual and was one of the reasons that meteorologists had trouble developing forecasts for Joaquin.

Detractors sometimes complain that any time the weather gets weird, somebody cries “climate change.” The reason for that is that an altered climate means weird weather. A climate is essentially the normal pattern of weather in a given area–or across the entire planet. When the pattern of typical weather changes, that is, by definition, climate change.

But what are the links between this particular weather event and the greenhouse effect?

Most directly, the sea is higher. Any time you get a storm surge, that surge is worse than it would have been because the sea starts out higher. The difference is only about eight inches (some areas see much greater effective rise because the land is also subsiding), but that is enough to have a huge effect. Anyone who doubts that should imagine the difference between zero and eight inches of water in their living room. Or, for that matter, the difference between zero inches and one inch! Last week’s storm pushed seawater up onto the land in South Carolina, North Carolina, Virginia, Maryland, Delaware, New Jersey, and Massachusetts. Today I saw, posted on Facebook, a video of a shark cruising down a flooded street in West Ocean City less than ten miles from my house. People who live in the affected areas can now go out and see exactly what climate change looks like simply by holding a ruler up to the high water marks. That’s about as unambiguous as it gets.

Secondarily, the sea over which Joaquin intensified was unusually warm–at least as of August, that area actually had record-breaking warmth. Warm water feeds hurricanes, so this pool of warm water explains Joaquin’s unusual strength. And Joaquin helps explain the huge amount of moisture in the un-named storm. Pools of warm water, like pools of warm air (heat waves) come and go, but global warming means they are more intense and more frequent now.

Third, a warmer planet means more extreme weather, including more extreme rain events. Again, the issue is frequency. This past week’s event was a thousand-year storm–that’s not a schedule but an expression of probability. The chance of such a storm occurring in any given year is about one in a thousand or 0.1%. Yes, it was certainly possible to get more than one per millennium, just as it’s possible to flip a coin and get heads seventeen times in a row, but you wouldn’t expect it. With extreme rain events happening more often, now we can expect these more often. I doubt this past week’s records will be broken any time soon, these things are still going to be pretty rare, but what isn’t going to be rare is the breaking of some record somewhere, especially those that involve precipitation (including snow!) or drought, or heat.

“We’ve never seen anything like this before!” is what climate change sounds like.



Bigger Floods in Texas, Reprise

Texas is flooding again, unfortunately.

Tropical Storm Bill formed in the Gulf of Mexico overnight and is–right now, as I write this–coming ashore between Houston and Corpus Christi. Bill is “only” a tropical storm, not a hurricane, but that ranking depends on wind speed, not on overall severity. Tropical storms, by definition, have sustained wind speeds somewhere between 40 and 74 miles per hour–any more, and they become hurricanes, which Bill will not do because these storms can generally only strengthen over water. Bill is not a very windy storm; its highest gusts are likely to be around 50 MPH. But the real problem is flooding.

Historically, most of the people who die in hurricanes and tropical storms drown.

The flooding is from two sources, rain and storm-surge, although the two interact in coastal areas if the storm surge makes it harder for rainwater to drain away. How much rain falls is not just a factor of how much moisture is in the clouds (typically a lot, but it can very) but also how big the storm is and how fast it moves. A large, slow storm takes longer to move over any given area and therefor rains more. Bill is about as wide as the Gulf Coast of Texas–big, but not monstrous. I have not learned whether it is slow-moving.  An old frontal boundary across Arkansas and North Texas will likely merge with Bill, adding more moisture to the system. A sickle-shaped area across parts of Texas, Oklahoma, Arkansas, Kansas, and Illinois is now under a flash flood watch. A much larger sickle of less severe rain reaches all the way to Maryland (which is ok, we need it).

Storm surges are caused by winds and pressure changes pushing along a dome of sea water. The surge looks something like a very rapid, unusually high tide–it can roll in within a few minutes. Before the modern era of accurate storm tracking, people sometimes went down to the beach to watch dramatic surf and then died as unexpected storm surges came in faster than they could run. Tropical Storm Bill’s winds are fairly modest, so its surge is only about four feet at the most, but the storm is rolling in at high tide–and we’re close to the New Moon right now, so this is one of the highest tides of the month. So, while we’re not looking at a monster surge by any means, Bill’s timing makes it worse than it might otherwise have been.

Again, this is weather, not climate. While human-caused climate change underlies all weather, just as a rising tide underlies all waves, this tropical storm is not, all by itself, a climate change story. So far, Bill looks like the same kind of storm the Southern US has always been vulnerable to. But what is a climate-change story is the context into which this storm is now moving.

First and foremost, Texas and Oklahoma are already soaked from weeks of intense, sometimes disastrous rain (following years of horrible drought). When the ground is already wet and rivers are already high, it doesn’t take much more rain to cause a major flood all over again. And while some flooding has always been a fact of life, the rapid swing from drought to weeks of torrential rain has all the hallmarks of the new, globally-warmed normal of extreme weather. It is because of this recent history of saturated ground that I am frankly worried about my friends and family in Texas right now.

Of course, Bill’s storm surge is also eight inches higher than it would have been were it not for sea-level rise–both from seawater expanding as it warms up and from the melting of glaciers. Eight inches might not seem like a lot, but imagine the difference between zero and eight inches of salt water inside your house.

Finally, according to a Alan Weisman, whose really neat book, The World Without Us, I have just read, the Gulf Coast of Texas is now uniquely vulnerable to storm surges because of the oil industry:

When oil, gas, or groundwater is pumped from beneath the surface, land settles into the space it occupied. Subsidence has lowered parts of Galveston 10 feet. An upscale subdivision in Baytown, north of Texas City, dropped so low that it drowned during Hurricane Alicia in 1983 and is now a wetlands nature preserve. Little of the Gulf Coast is more than three feet above sea level, and parts of Houston actually dip below it. –p. 143

So, a storm surge coming ashore near Galveston of “only” two to four feet is really serious business. Petrochemical extraction is not itself climate change, but it’s obviously intimately related.

This is not the first Tropical Storm Bill, nor will it be the last. Meteorologists reuse storm names, only retiring those that, like Katrina, become particularly note-worthy. None of the previous Bills has earned that distinction, and this one probably won’t, either. But we live in a world where even modest storms are more destructive than they might otherwise have been.