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.