The Atlantic Meridional Overturning Circulation (AMOC), sometimes nicknamed "the Atlantic Conveyor," is an enormous oceanic current that not only encircles the entire Atlantic Ocean, it links up with other circulation patterns in the Indian and Pacific Oceans.
It's called a "thermohaline" circulation because it's driven by two things; temperature and salinity. Cold water is denser than warm water; salty water is denser than fresher water. Alterations in these factors determine where the water goes, setting up convection (the movement of a fluid because of gradients in density). Specifically, as the warm Gulf Stream (the red line along the eastern coast of North America on the above map) moves northward, it cools down and evaporates. Those both act to increase its density, to the point that just south of Iceland, it sinks.
That sinking mechanism is what drives the entire thing. Slow that down, and the whole system fails.
Which is exactly what is happening. A paper last week in Nature found that the AMOC has diminished dramatically because of anthropogenic climate change; the warming oceans, along with fresh meltwater from Greenland, has made large parts of the north loop of the circulation too buoyant to sink. Since 1950, the flow rate has gone down by 0.46 sverdrups. Before you say, "Well, that doesn't sound like very much," allow me to point out that one sverdrup is a million cubic meters a second. The combined flow of all the rivers in the world is only about 1.2 sverdrups.
So 0.46 is huge.
Current models indicate that this change is going to have enormous effects on local climates. Western and northern Europe are likely to get colder; the surface loop of the AMOC is why Iceland, Scotland, and Scandinavia are way warmer than you'd expect given their latitudes. The southeastern United States and eastern South America will probably become much warmer; the heat energy doesn't just go away because it's not being transported northward and dissipated. Rainfall patterns, and storm paths and intensity, will certainly change, but how is unknown.
The truth is, we don't know enough to predict exactly what the outcome will be, at least not with any certainty. We're perturbing a complex global system with about as much caution as a toddler playing in the mud. But what seems certain is that we have now entered the "Find Out" phase of "Fuck Around and Find Out."
What kills me is we've been warning about this for decades. British science historian James Burke's prescient documentary After the Warming described the collapse of the AMOC as an outcome of anthropogenic climate change all the way back in 1991. But instead of listening to the scientists, and brilliant advocates like Burke who bring science to the public notice, more people were swayed by idiots like former Oklahoma Senator James Inhofe, who brought a snowball onto the floor of the United States Senate and basically said, "Hey, it's snowing, so climate change isn't real, hurr hurr hurr durr."
Of course, listening to Inhofe and his ilk is easy. If you believe him, you don't have to make any changes to your lifestyle. And we haven't gotten any further in the intervening decades; President-elect Trump has nominated Lee Zeldin for the head of the Environmental Protection Agency and Doug Burgum for Secretary of the Interior, both thoroughgoing climate change deniers who are deep in the pockets of the fossil fuel industry. (And please, for the love of all that's holy, stop calling them "climate skeptics." A skeptic respects the evidence. These people reject a body of evidence that's as high as Mount Everest in the name of profit and short-term expediency.)
I read a serious analysis of Donald Trump's win claiming that one factor was that Americans have a "suspicion of expertise." That is something that will never, ever make sense to me. How is it reasonable to say, essentially, "These people know more than I do, so I don't believe them"? The result is that we now have one of the most powerful countries in the world being run by a cabal of people who are united by two things -- (1) devotion to Donald Trump, and (2) a complete lack of qualifications. So this distrust of evidence, science, and rationality is only going to get worse -- and will become the motive force in driving policy.
The problem is, though, if you ignore the truth, sooner or later it catches up with you. And from the recent paper, it appears it's going to be sooner. Sea level rise is already threatening coastal communities, and there are island nations that will simply cease to exist if if gets much worse. Extreme weather events are likely to become commonplace. We're sure to see alterations in climate that will affect agriculture, and in some places, habitability.
As usual, the people creating the problem aren't the ones who are going to get hurt by it -- at least not at first. But this is an issue that will, ultimately, affect us all.
And lord have mercy, I am tired. Tired of shouting warnings, tired of citing study after study, tired of arguing from the standpoint of facts and evidence with people determined not to listen to any of it. I'm not even an actual scientist, just a retired science teacher and blogger, and I feel like I've been sounding the call about this stuff forever; I can't imagine how the actual researchers feel. It makes me sympathize with Cassandra, from Greek mythology -- who was blessed with the ability to see the future, but cursed to have no one believe her.
I wish I had some sort of hopeful message to end on, but I don't. I'm not naturally a pessimist, but given the fact that the country I live in just voted in an anti-science, anti-intellectual, anti-academic administration whose motto seems to be "Corporate Profit Über Alles," I don't think we're going to make any progress here for the next four years. By then, how much more damage will have been done?
As journalist Sheri Fink put it: "Soon after a disaster passes, we tend to turn our eyes away and focus our resources on the day-to-day, rather than on preparing for the rare, but foreseeable and potentially catastrophic disaster. It's another form of triage, how much we invest in preparing for that, a very important question for public policy. But... we are such a short-sighted species."
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