“Shukhov went to sleep fully content. He’d had many strokes of luck that day: they hadn’t put him in the cells; they hadn’t sent his squad to the settlement; he’d swiped a bowl of kasha at dinner; the squad leader had fixed the rates well; he’d built a wall and enjoyed doing it; he’d smuggled that bit of hacksaw blade through; he’d earned a favor from Tsezar that evening; he’d bought that tobacco. And he hadn’t fallen ill. He’d got over it.
A day without a dark cloud. Almost a happy day.”
From: One Day in the Life of Ivan Denisovich, by
(Art for this post was draw by Gencraft.com AI, prompts were variations on boiling a frog.)
Just did my usual AQI check today …
… looking up the PM 2.5 level, before heading out to the garden. It was 64, for fine particulates. Not too bad. You hardly even notice the smoke in the air from the unprecedented Canadian forest fires.
A day without a dark cloud. Almost a happy day.
My usual AQI check? Not too bad?
Good lord, this is my new normal. When by recent historical standards — as in the past decade — this is a terrible day for breathing in fine particulates.
Source: Analysis of data from EPA.gov website, air pollution plots for your choice of area.
When (not if) the Gulf Stream stops …
Then I sat down to read the news, and stumbled across articles on the latest research on the Atlantic Meridional Overturning Circulation, or AMOC. Part of which is the U.S. Gulf Stream. And which, in turn, is part of the earth’s overall thermohaline circulation, the network of ocean currents that transports heat around the ocean from tropics to poles.
Below, red represents warm surface currents, blue is cold ocean-bottom currents.
Source: Via Wikipedia. By Robert Simmon, NASA. Minor modifications by Robert A. Rohde also released to the public domain – NASA Earth Observatory, Public Domain, https://commons.wikimedia.org/w/index.php?curid=3794372
In a nutshell:
- The Gulf Stream has a tremendous impact on world climate, particularly for the U.S. and Europe.
- It is slowing down.
- It is becoming less stable.
- Both of those were expected (predicted by climate general circulation models) as global warming progresses.
- The same models more-or-less predict that it’s only a matter of time before the Gulf Stream markedly slows or shuts down entirely, if global warming is allowed to progress.
- How much time is a matter of true uncertainty and scientific debate.
- What was not expected is that the fresh water runoff from the melting of the Greenland ice sheet would accelerate the AMOC slowdown, a lot.
- That ice sheet melting melting is only going to get worse.
Consequences?
Question: What major U.S. cities are on the same latitude north as London, England?
Answer: None. London (51 degrees N) is further north than the northernmost tip of Maine. London is about as far north as Winnepeg, Ontario (~ 50 degrees N latitude). It’s about ten degrees further north than Chicago (~ 42 degrees N).
Here’s a nice map from Energy Innovation:
Stop delivering a steady stream of warm water to London’s doorstep, and a lot of things are going to change, in a hurry, and not for the better.
The forgotten 2010 hiccup in the Gulf Stream
I’ve been tracking the evolution of scientific thinking about the future of the Gulf Stream for quite a while.
Back in the day — the day being about a decade ago — the consensus of climate modeling and analysis is that if global warming progressed unchecked, there is a high probability that the AMOC/Gulf Stream would slow profoundly or shut down within three centuries. But there was essentially zero chance that it would shut down any time this century.
Then some clever researchers pointed out that climate models commonly used to analyze the AMOC didn’t account for the huge input of fresh water near the North Atlantic terminus of the AMOC, due to the melting of the Greenland Ice Sheet. That screws up the “haline” part of the thermohaline circulation. It dilutes the salt content, making the water less dense, and so less willing to sink to the ocean bottom as fast as it used to.
That 2017 analysis showed that once you factor that in, it’s possible you might see the AMOC/Gulf Stream shut down entirely in this century. This has become, I believe, by a small margin, the consensus of thinking about this issue. So complacency about the Gulf Stream, for our generation, is no longer fully warranted.
Could a little melting do that? Consider that the flow of the Mississippi is less than 0.02 Sverdrups, or million cubic meters of water per second (reference Wikipedia). By contrast, the melt from the Greenland ice sheet is currently around 0.04 Sverdrups. Its as if Mother Nature has created a brand new river, twice the flow of the Mississippi, discharging directly into the northern terminus of the AMOC/Gulf Stream.
You can read a concise writeup of that 2017 research on RealClimate, a site run by real climate scientists.
Meanwhile, melting of Antarctic ice is putting a plug on the other end of the AMOC, by overlaying a light-density fresh-water lens on an area where the other end of the AMOC is supposed to rise to the surface. In both cases, you end up with a big blob of fresh(er) water that wants to stay put, rather than go with the flow.
So it was just six years ago when somebody refined a climate model to include the effects of Greenland ice sheet meltwater runoff. And so just six years ago when the best estimate shifted from “centuries from now” to “maybe this century”.
Today we have newspaper reporting about recent analysis of instability in the AMOC that suggests that odds are we will see the shutdown occur this century. The range of plausible times for a shutdown of circulation spans 2025 to 2095. The headline is sensationalistic, but the message is nevertheless interesting.
Ahem, 2025? The threat begins a couple of years from now?
Obviously, the Guardian click-baited the headline. But as discussed above, this latest news is just one more step in the progression that’s been going on for the past couple of decades. As climate modeling of ocean currents has become more refined, the shutdown of the AMOC/Gulf Stream has gone from far-off potential occurrence, to something that might happen this century, to something that’s starting to look like a near-certainty to occur this century. And now, to something that has a (very low) chance of occurring a few years from now.
What I’m saying is, when you put it in context, this latest progression in the scholarly literature is not that out-of-line with recent history. Doesn’t mean that it’s correct. But does bring up what occurred at the end of 2009.
The 2009/2010 hiccup in the gulf stream.
One of the least-appreciated aspects of the Gulf Stream is that it lowers sea levels on the U.S. East Coast. I’m a bit hazy on the details, but in a nutshell, owing to something like the Coriolis Effect, as it travels up the U.S .East Coast, the eastern (seaward) side of the Gulf Stream is somewhere around four feet higher than the western (landward) side.
Source: The link between the Gulf Stream and coastal sea level as seen in observations and models. Tal Ezer, Center for Coastal Physical Oceanography (CCPO). Department of Ocean, Earth and Atmospheric Sciences (OEAS). Old Dominion University, Norfolk, VA, USA
That isn’t new information, by the way. That’s been recognized since at least the 1930s, as the research cited above points out.
So, as a matter of logic, if the physics of that flowing water drops U.S. East Coast sea level by about four feet, then, wouldn’t you see four feet of sea level rise if that water quit flowing entirely?
Is four feet a lot? I should probably ask my my wife, who inherited an ancient ground-level time share in Ocean City, Maryland. The ground for which is about six feet above sea level. Or about typical for Ocean City. The time-share might still be there. But the road leading to it would be under sea water. (Source for images: NOAA sea level rise viewer.)
We got a preview of that in 2009-2010. The Gulf Stream temporarily slowed by about 30 percent. And sea level rose nearly half-a-foot north of New York City. And by similar amounts along much of the U.S. east coast.
Source: Goddard, P., Yin, J., Griffies, S. et al. An extreme event of sea-level rise along the Northeast coast of North America in 2009–2010. Nat Commun 6, 6346 (2015). https://doi.org/10.1038/ncomms7346
Sea level is variable. The flow of the Gulf Stream is variable. But this event was large enough to stand out clearly against background variation. It’s very much small practical demonstration of what would ensue if the Gulf Stream were to stop entirely.
Finally, I’ll point out that while there has been a long-term trend toward a slowing of the Gulf Stream, that 30% dip in 2009-2010 came out of the blue. Nothing predicted it. And, for all we know, an event like that will happen again soon.
Conclusion: What’s it gonna take?
There’s ample evidence of periods of abrupt climate change in the past. In particular, there have been episodes of abrupt change during the warming period of the ice-age cycle that we’re in now.
So it’s really not a question of whether we’ll ever see any abrupt climate change events. It’s more a question of when. The National Academies of Science put it pithily: Abrupt Climate Change, Inevitable Surprises. If nothing else, anything that threatens global food supplies constitutes a threat to U.S. national security. And abrupt climate change could certainly do that.
That frog is going to get boiled, sooner or later. I say, the sooner that’s boiled, the better. The more fully-cooked frogs we see, maybe the more we’ll be willing to do something about it. Instead of thinking that it’s normal.
