From ARS Technica
We aren’t likely to see it happen, but it’s still sobering.
Scott K. Johnson – 2/25/2019, 6:13 PM
Stratocumulus clouds, like those in the lower two-thirds of this image, are common over the oceans.
The word “hysteresis” doesn’t immediately seem threatening; it hints at a portmanteau of “history” and “thesis”—a dense read, perhaps, but those never killed anyone. But that’s not what the word means. Hysteresis is a profound behavior some systems can display, crossing a sort of point-of-no-return. Dial things up just one notch, and you can push the system through a radical change. To get back to normal, you might have to dial it down five or six notches.
Earth’s climate system can provide examples. Take the conveyor-belt-like circulation of water in the Atlantic Ocean. Looking back at the past, you can see times that the circulation seems to have flipped into an alternate pattern regarding climatic consequences around the North Atlantic. Switching from one pattern to the other takes a significant nudge, but reversing it is hard—like driving up to the top of a ridge and rolling down into the next valley.
A new study led by Caltech’s Tapio Schneider may have identified a disturbing hysteresis in Earth’s climate—a shift in cloud patterns in response to warming that could quickly heat the planet much further. If we were to continue emitting more and more greenhouse gas, we’d eventually end up running this experiment for real. (Let’s not, please.)
Cloud services
The center of this drama is a particular type of cloud. Stratocumulus clouds typically blanket about a fifth of the low-latitude ocean. Most clouds are formed because air warmed by the Earth’s surface (or forced over mountains) cools as it rises, condensing water vapor to cloud droplets.
Stratocumulus clouds are a little different. The convection that lifts their moisture isn’t driven by warming at the bottom but by cooling at the top.
The water in this cloud deck absorbs much of the infrared radiation emitted upward from the warm surface. The cloud deck re-emits some radiation back downward and some into outer space. The air above these clouds is drier and absorbs much less of the outgoing energy passing through it. That means you can think of these clouds like the cooling fins of a radiator. They shed more heat upward than they receive from the atmosphere above them, allowing them to cool off from the top down. The cold air at the top of the clouds sinks, setting up a convection loop that brings water vapor up from the sea surface to the cloud deck.
So, what happens to this unique process in a warmer world?
Nothing but blue skies
To tackle this, Schneider and his colleagues flipped things around. They utilized a model that can simulate these clouds in a small patch of atmosphere—given a simplified version of the world around them. Specifically, they simulated a patch of the subtropical ocean with stratocumulus clouds above and a neighboring patch of tropical ocean responding to global warming. They did this for varying concentrations of greenhouse gas equivalent to 400 parts per million of CO2 (similar to today) on up to 1,600 parts per million.
Up to about 1,000 parts per million, there were no major surprises. Things got around 4°C warmer and numbers changed for things like water vapor and cloud altitude. But the cloud deck generally looked familiar.
At about 1,200 parts per million, however, the simulated clouds suddenly dissipated. And without that shade reflecting sunlight, the world warmed another 8°C.
Processes responsible for the cloud deck breaking up around 1,200 ppm CO2 in the model. Temperatures shown in units of kelvins.
Schneider et al./Nature Geoscience
How is CO2 flipping the switch on these clouds? The researchers found a pair of simple processes working together in their simulation. First, warmer air carries more water vapor up from the sea surface, and when that water vapor condenses, it releases a lot of latent heat. That extra latent heat gives the air a little buoyancy boost, increasing the turbulent movement that can mix dry air from above into the cloud layer. This dries out the cloud deck and makes cloud formation less likely.
“Hysteresis” isn’t some terrible “profound behavior … crossing a sort of point-of-no-return.” It’s common in many (if not most) natural systems and is nothing more than a situation where future conditiond=s depend at least partially on past conditions. It is certainly not any sort of “point ofm no return”. It is usually possible to return to some original state, just not along the original path. In fact, the phrase “hysteresis loop” refers to a path that repeatedly cysles through a sequence of states.
The article attempts to paint hysteresis as related to hysteria when they have completely different derivations and a similar only in sound and spelling.
You nailed it! In a magnetic material when an H field is applied the B field moves to a certain point in the H,B coordinates. When H is removed, i.e. goes to zero, B doesn’t go back to zero. To get B to go to zero you must apply a negative H field. If the field is of the same magnitude as the original field then B will go through zero and to a negative value, an antipode of the original starting point if you will. If H is then taken to zero B remains at the negative value.
To get B to zero a positive H field needs to be applied again and removed before B goes positive again. Or, just apply the original positive H field and let the B field go back to its starting point. That’s why it is called a hysterisis “loop”.
What this study does is assume that water vapor is at a certain value on the vertical axis because of some physical process and then some other process removes all the water. I.e. Water vapor goes to zero. It never seems to consider that the original forces will move the water vapor back to its original level. A hysterisis LOOP. In other words they only modeled part of the hysterisis loop and made a conclusion they had found a tipping point! Partial models that don’t consider the entirety of a hysterisis loop can be made to show almost anything, e.g. perpetual motion.
And yet there have been several times when CO2 was above 1200 ppm (some during ice ages), and the dreaded problem apparently didn’t happen. Hmmm.
I would appreciate it if one of the mathematicians who comment here could briefly address the constant references to “tipping points.” My understanding is that, in chaos theory these are usually called phase changes. Furthermore, my understanding is that chaos theory indicates two important things or properties about these “tipping points”: 1) their timing is not predictable; and 2) their SIGN is not predictable. If this is true, any talk of “tipping points” that implies predictability for either of these two properties is nonsense.
Thanks again for any brief explanation for this engineer. I even dug up Lorentz seminal paper “Deterministic Nonperiodic Flow.” Quite a slog for me but if I understood it correctly is seems to imply my idea about “tipping point” predictability is pretty close.
When you look at their graphic, the proposed mechanism for damping convection is the elimination of the lapse of temperature with altitude. One might fairly ask why the surface is not commensurately warmed, maintaining the lapse and convection.
The answer seems to be that this study is a reincarnation of the “mid tropospheric hot spot”. This hot spot has been routinely predicted for increasing atmospheric CO2 by generations of models, but it has never been seen in satellite or balloon measurements.
Correct the model so it does not show a mid level hot spot and so it does not run hotter at the surface than observations at current CO2.
Run the experiment again.
the people running our climate have grown used to ‘calculating’ that which has never been measured first….
Actually the “hot spot” is (suppsed to be) caused by a decreasing lapse rate in turn caused by increasing water vapor. Air with more water vapor has greater heat capacity and lower average molecule weight and therefore cools less when rising a specific distance. The absence of a hot spot proves that there is no “water vapor feedback”, at least in the tropics.
The lapse rate can never be eliminated in an atmosphere containing greenhouse gases as long as the sun is hining.
OH NO — clouds are going to tip over….
“Striking study finds a climate tipping point in clouds” –> Should more accurately read:
“Predictable psuedo-science “study” finds “tipping point” in climate models that assume the real climate has any “tipping point” with regard to something that has never caused such a “tipping point” in the past.”
Alan Tomalty February 26, 2019 at 10:34 pm
I guess I’m a simpler mathematician.
1958 – Co2 310ppm, 2019 – Co2 412ppm = an additional 102ppm / 61 years = 1.67ppm/yr.
1,200ppm Co2 – 412ppm = 788ppm. 788ppm / 1.67 = 472 years…
So in the year 2491 all of this one type of cloud will disappear.
Damn, there goes all the good sunset pictures….
Nonsense, but with a model you can make anything up you want.
Firstly, 1,000 ppm CO2 can never cause water (ocean) to warm 4c, not even close.
Secondly, 1,200 ppm C02 causing a further 8c rise would lead to the warmest period in Earth’s history ever known with life, beating warm oceans circulating over the poles with no polar ice caps or glaciers.
Thirdly, there has been zero evidence of this occurring any time before, when CO2 levels were higher than 1200ppm CO2.
Fourthly, this initial warming is similar to what occurs with ENSO over the Tropical ocean where it warms more than 3c with a strong El Nino.
Fifthly, the warmest climates over the past hundreds of millions years ago were due to different continental land and ocean positioning with different ocean currents changing albedo hugely.
ENSO occasionally causes rises in Tropical ocean temperatures above 3c and the result is more cloud formation and heavier rains/thunderstorms.
Yes. Stratus clouds are very typical over cool oceans offshore of dry, hot land. For example on the coasts of Peru or Namibia or around the Galapagos.
In such areas they are so persistent that a special vegetation belt forms at the level where they usually lie, that is sustained solely by the fog, while lower levels are arid, because it almost never rains from such clouds.
1000 or 1200ppm carbon dioxide does not seem so bad…
“”As plant communities expanded onto land to form the first forests, they depleted the carbon dioxide (CO2) that was in the atmosphere,” Waters said. “CO2 levels dropped to 400 ppm toward the end of the Devonian. It got colder. There were glaciation events and the rapid change in the climate caused severe extinction in the tropics and the existing coral reefs became extinct.” By comparison, the world’s current CO2 level is very close to 400 ppm.”
from….https://www.sciencedaily.com/releases/2013/12/131213092841.htm
“That extra latent heat gives the air a little buoyancy boost, increasing the turbulent movement that can mix dry air from above into the cloud layer. This dries out the cloud deck and makes cloud formation less likely.”
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And because the energy balance must be balanced for well-known reasons, the oceans have to contribute slightly to warming the atmosphere – a Zero-sum game.