Tipping Is Optional

Guest Post by Willis Eschenbach

I was greeted this morning by a CNN headline saying “Critical Atlantic Ocean current system is showing early signs of collapse, prompting warning from scientists“. YIKES! Be very afraid.

The CNN article opens by saying:

A crucial system of ocean currents may already be on course to collapse, according to a new report, with alarming implications for sea level rise and global weather — leading temperatures to plunge dramatically in some regions and rise in others.

Scary stuff, all right. It is referring to a study in Science magazine, Physics-based early warning signal shows that AMOC is on tipping course.

It’s the resurrection of another “tipping point” scare. And of course, despite the title, rather than being “physics-based” this study is actually “model-based”. It’s a study of the Atlantic Meridional Overturning Current (AMOC). Here’s what the AMOC looks like.

Figure 1. The Atlantic Meridional Overturning Current (AMOC). Red is surface currents, orange is descending, blue is deep return currents. Graph at the bottom shows the AMOC flow measured at 26.5°N, in units of Sverdrups (abbreviated “Sv”, 1 Sv = 10⁶ cubic meters per second)

Well, actually, they do start out with physical measurements, viz:

Continuous section measurements of the AMOC, available since 2004 at 26°N from the RAPID-MOCHA array, have shown that the AMOC strength has decreased by a few Sverdrups (1 Sv = 10⁶ m³ s⁻¹) from 2004 to 2012, and thereafter, it has strengthened again.

Not mentioned is that this increase in the AMOC strength has continued up until the latest study in 2018. So in the real world, there’s no indication of any collapse in the AMOC. There’s no “tipping point” in sight, it’s actually slightly strengthening … go figure.

So why do they say there’s a possible tipping point that could lead to a collapse?

A model, of course. In this case, it’s the CESM, the Community Earth System Model. What they did was to start up the model, then add modeled freshwater very gradually to the modeled North Atlantic, presumably simulating a melting of the Greenland ice or somesuch which might shut down the AMOC. Here’s their description:

A quasi-equilibrium approach is followed by adding a slowly varying freshwater flux anomaly F_H in the North Atlantic over the region between latitudes 20°N and 50°N. This freshwater flux anomaly is compensated over the rest of the domain, as shown in the inset of Fig. 1A. We linearly increased the freshwater flux forcing with a rate of 3 × 10⁻⁴ Sv year⁻¹ until model year 2200, where a maximum of F_H = 0.66 Sv is reached.

And what did they find? Well, they found that in the model year 1,758, which in our terms is the year 3782 AD, the AMOC fell off a cliff.

IMPENDING TIPPING POINT CATASTROPHE IN 3782 AD! EVERYONE PANIC!!!

Figure 2. Model results showing AMOC tipping point. Figure 1A from the study linked above.

Now if you follow my work, you’ll know that I often ask the most impertinent questions. So I got to thinking about something they neglected to mention … just how much modeled fresh water have they added?

Trigger Warning: the next part involves that dreaded creature “math”, so if you’re allergic to math, just skip to the last line of the bold section below …

To continue with the mathiness, when the tipping point occurred in 3782 AD, they were adding 0.527 Sverdrups (“Sv”) of fresh water (top scale, Figure 2). That means on average over the entire period up to the tipping point, they were adding half of that, 0.264 Sverdrups.

Now, a Sverdrup is a million cubic meters per second. So over the 1,758 model years from the start up to the tipping point, they’ve added a total of:

0.264 Sv * 10⁶ cubic meters per second/Sv * 1758 years * 31,556,926 seconds per year / 10⁹ cubic meters per cubic kilometer =

14,629,305 cubic kilometers of modeled fresh water added.

Now, fourteen million cubic kilometers of water, that’s a very big number. So let’s compare it to something that’s also very big … say the total volume of water in the entire Greenland Ice Cap. Here’s that comparison.

Figure 3. Comparison of the volume of water contained in the Greenland Ice Cap with the volume of freshwater added to the model from the start of the run until the tipping point.

The mind boggles … like I said, tipping is optional …

Not much else left to say about that. I’m reminded of two of Mark Twain’s quotes, viz:

The reports of my death are greatly exaggerated.

and

The Mississippi between Cairo and New Orleans was twelve hundred and fifteen miles long one hundred and seventy-six years ago. . . . Its length is only nine hundred and seventy-three miles at present. …

In the space of one hundred and seventy-six years the Lower Mississippi has shortened itself two hundred and forty-two miles. That is an average of a trifle over one mile and a third per year. Therefore, any calm person, who is not blind or idiotic, can see that in the Old Oolitic Silurian Period, just a million years ago next November, the Lower Mississippi River was upwards of one million three hundred thousand miles long, and stuck out over the Gulf of Mexico like a fishing-rod.

And by the same token any person can see that seven hundred and forty-two years from now the lower Mississippi will be only a mile and three-quarters long, and Cairo and New Orleans will have joined their streets together, and be plodding comfortably along under a single mayor and a mutual board of aldermen.

There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.

In closing, here’s a bit of history regarding so-called “tipping points” from the unquestioned king of climate alarmism, NASA’s very own Dr. James Hansen …

Riiight …

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Here in our redwood forest home near the Northern California coast, the giant storms of the Pineapple Express have rolled on by. Torrential rain, gale-force winds. We were without power for five days, trees and power poles down everywhere. Our fossil-fueled generator worked like a champ … and after the storm, today is sunny. So I climbed onto the roof, cleaned the gutters, and washed the skylights. What’s not to like?

My very best to all,

w.

As Usual: I ask folks to quote the exact words they’re discussing, it avoids endless misunderstandings.

My Other, Often Controversial, Writings: My blog is “Skating Under The Ice: A Journal of Diagonal Parking in a Parallel Universe“. And over on X, aka Twitter, I just today got my 10,000th follower … @weschenbach for those interested.