We can draw an example from weather forecasting. The accuracy of the long term forecast is highly dependent on the accuracy of the short term forecast. Consider a seven day forecast. If the first 24-48 hrs. is incorrect, by even a small factor which is somehow missed, this will likely make the later portion completely irrelevant so that it's not even close. But if the first 48 hrs. hold true to the forecast, the later period will likely just need small changes. What this indicates is that a very slight, unforeseen change, in the very near future will render any long term model which does not account for it, completely useless. The closer in time to the beginning point of the forecast period, the unforeseen factor is, the smaller it needs to be, to have a large affect on the accuracy of the long term. This could be like the "trigger point" you referred to earlier.

What this indicates is that a very slight, unforeseen change, in the very near future will render any long term model which does not account for it, completely useless. — Metaphysician Undercover

True. I want to review some articles on long-range forecasting. It's fascinating stuff. I was hinting earlier about why the latest models are better, because they include previous research into how to weight factors.

Then I want to discuss one article on the 100,000 year problem and a startling implication of its proposed solution. If the 100,000 year cycle is a result of a change in ocean currents that further cooled the surface of the earth, this means reglaciation is now being triggered by a shutdown of the oceanic heat conveyor, the very same oceanic current that is slowing now due to global warming. No scientist is predicting a shutdown, but if it did, reglaciation would be triggered.

If nothing else, it's a cautionary tale about being certain of the future of the climate.

The general principles involved in ocean currents can be described. First, the prevailing wind at the equator is from the east, due to the spin of the earth, the air doesn't spin along with the earth fast enough to keep up with the earth, so there is a constant wind from the east. This pushes the warm water at the equator, which is the most heated from the sun, toward the west. It naturally curves away from the equator, to the right in the north, and the left in the south, as the Coriolis effect. So in the northern hemisphere, surface water moves northward along the east coast of the large continents, and southward along the west coast This brings heat toward the poles in a way which is sort of like convection, but the principal source of the wind is the mechanical spinning of the earth, rather than a convective wind. This is important, the principal "weather maker" is the mechanics of a spinning body with oceans and an atmosphere, solar heating and convection are secondary.

The surface currents of the oceans would be a simple process, except the surface water is forced away from the equator by the winds of the spinning body, and there is no such force to bring replacement surface water, from the north and south. That's why it's different from convection which is solely temperature driven. So much of the replacement water, at the equator, has to come from the depths. This creates flows in the depths, and these flows are not well understood. El Nino is known as a slowing of this flow of cold replacement water along the west coast of South America.

You can see that the real cycle is not a flow of surface water, but the cycling of water from the surface to the bottom, and back to the surface. It is very complicated because there are many layers and the layers are not necessarily vertical, as it is a three dimensional activity. We can imagine principles similar to air movement, but on a slower scale, horizontal winds, vertical convections, and the movement of distinct "air masses" (water masses in this case). None of these activities are well understood.

Yes!

It looks like this:

There's a theory that once we came out of primarily Milankovitch forcing, the 40,000 year cycle, to an orbital forcing cycle of 100,000 years, shutdown of this oceanic heat conveyor became the trigger for reglaciation.

This means the Northern Hemisphere summer insolation minimum isn't the main trigger, it just lowers the threshold. We're in that low threshold period now, and the ocean currents are slowing down due to global warming.

This means the forecast could be worse than just global warming. We could be headed for a period of extreme volatility.

Long range climate modeling has been going on for a couple of decades. It's now made easier by increased computing capabilities and knowledge about the factors involved in reglaciation, but unknowns still abound. Any model starts with some basic assumptions and data from the climate of the past, then variables like pCO2 can be tweaked to give projections.

A model known as CLIMBER-2 was created in 2005. It assumes that reglaciation is triggered by a minima in summer insolation in the Northern Hemisphere.

This model predicts an unusually long interglacial even without an increase in pCO2 forcing. With a 5000 Gton increase in CO2, the climate comes out of the glacial/interglacial cycle completely for at least 500,000 years.

One possible answer as to why the model is predicting such a long interglacial (50,000 y) even with baseline pCO2 might be that the so-called Anthropocene didn't start in the 1800s. It might have started with human agriculture as long as 6000 years ago. Here.

It looks like this: — Tate

That map is extremely vague, just showing some generalities. It's not at all useful for any attempt to determine anomalies. The whole concept of "oceanic heat conveyor", is equally vague, and overly generalized. The oceans are always going to convey heat, so long as the earth is spinning, and the sun is heating, that's what the oceans do. What is at issue, if you are talking about a potential trigger point, is minute peculiarities, and changes to how the oceans convey heat. Since the vast majority of oceanic flow is well below the surface, the information is not available to produce an adequate model. That's why El Nino cannot be accurately predicted, it is a feature of the upwelling of cold water, resulting in a change in surface temperature.

We're in that low threshold period now, and the ocean currents are slowing down due to global warming. — Tate

I really see no reason why warming would cause ocean currents to slow down, because the earth would continue spinning. It could cause changes to them, perhaps even speed some up.

The whole concept of "oceanic heat conveyor", is equally vague, and overly generalized — Metaphysician Undercover

That's just one way to refer to that particular set of currents. It's also called the thermohaline circulation.

What is at issue, if you are talking about a potential trigger point, is minute peculiarities, and changes to how the oceans convey heat — Metaphysician Undercover

The circulation requires a heat differential between surface and bottom water in the north Atlantic. As that area cools due to polar ice sheet melting, the differential is minimized. Scientists are presently keeping a close eye on it because the ocean currents are slowing.

I touched on this earlier: climate models are not crystal balls. They're based on a few assumptions, some best guesses, and a lot of data.

Computers just enhance our ability to make predictions from what we know now.

The circulation requires a heat differential between surface and bottom water in the north Atlantic. As that area cools due to polar ice sheet melting, the differential is minimized. Scientists are presently keeping a close eye on it because the ocean currents are slowing. — Tate

Actually, I don't think the circulation requires a heat differential at all. As I explained, it is the product of the spinning planet. The heat differential is created by the uneven heating of the planet, by the sun, but this is not required for the circulation, which is caused by the spinning of the planet, not the heating of it.

And, it is really not accurate to say "ocean currents are slowing", because the currents are not at all stable, they are always in flux, constantly changing. While one current slows down a bit, another speeds up. So long as the earth is spinning, the water is flowing, and the moving water will transport heat when the surface is unevenly heated.

Actually, I don't think the circulation requires a heat differential at all — Metaphysician Undercover

The thermohaline circulation does. It was in the link.

As you recall, the CLIMBER-2 model uses insolation minima as the primary driver of ice sheet nucleation. As one of its creators asked: 'What else would cause it?'

There are several articles out now that have called this assumption into question. For one: insolation is at a minimum now and there's no reglaciation starting. Another is that the geological record doesn't back up this assumption.

So what else could be causing reglaciation if not insolation minima?

A lot of articles are pointing to this:

"Understanding long-term history of North Atlantic intermediate to deep water circulation is important for assessing of the role of the thermohaline circulation (THC) in global climate change. Today, North Atlantic Deep Water (NADW) ventilates more than half of the volume of the deep oceans, affecting the physical and chemical properties of deep water globally. A growing body of geological and geochemical evidence demonstrates that at certain times in the past, the production of NADW, and with it the climate of the circum-Atlantic, changed at rates and with magnitudes that are of societal relevance. During the most recent glaciation, large reorganizations in the circulation of the North Atlantic Ocean and the Nordic Seas mirrored variations in air temperature over Greenland, suggesting that ocean circulation was tightly linked to North Atlantic climate over both glacial-interglacial and shorter timescales". Here

Models have previously left out consideration of slowing or shutdown of the thermohaline circuit. Since a number of scientists are now considering the possibility that this has been the real trigger for reglaciation since we entered the 100,000 year cycle, I imagine we'll be seeing those models soon.

From here: the ocean heat conveyor is presently slowing down. Scientists aren't prepared yet to say it's about to stop, but they're watching it closely.

If it did stop, it's possible that reglaciation could begin. We're at the right point in orbital forcing for another glacial period to take hold, which would soon drop the pCO2 in the atmosphere by cooling the oceans.

Just food for thought. If you want to discuss further, or get access to articles that are behind paywalls, let me know.

One of the things I've recently realized is the way this kind of information could confuse the global public. I could see a backlash developing against climate science, which would be unfair. Scientists always go on what they know and understand at the time. This doesn't cause problems in astrophysics or biology, but when you have an intensely publicized and even politicized science like climatology, it's another story.

There have already been articles about climate scientists encountering resistance to a free exchange of ideas. Imagine that the thermohaline slows down even more than it has. Imagine scientists trying to explain that we're headed toward an event at least like the Little Ice Age, and possibly like the Younger Dryas, which would be devastating to the human population of the earth.

Instead of packing up and moving to Greenland, people would be returning to our original home: Africa, specifically, the Sahara.

The thermohaline circulation does. It was in the link. — Tate

The thermohaline circulation is not an ocean current, nor is it a group of currents. As I said already, it's a vague and extremely general abstraction, which is not at all useful for prediction purposes.

And, it is very common for THC to lead to faulty predictions.

And, it is very common for THC to lead to faulty predictions. — Metaphysician Undercover

Not to mention munchies and long drawn out philosophical discussions.

Let's, as any person with even a modicum of intelligence would say, the first port of call is to set your own house in order/medici, cura te ipsum.

So, getting down to the brass tacks, a question: Is philosophy good/bad for the climate?

:snicker:

In the Earth's polar regions ocean water gets very cold, forming sea ice. As a consequence the surrounding seawater gets saltier, because when sea ice forms, the salt is left behind. As the seawater gets saltier, its density increases, and it starts to sink. Surface water is pulled in to replace the sinking water, which in turn eventually becomes cold and salty enough to sink. This initiates the deep-ocean currents driving the global conveyer belt.

https://oceanservice.noaa.gov/education/tutorial_currents/05conveyor1.html#:~:text=These%20deep%2Docean%20currents%20are,very%20cold%2C%20forming%20sea%20ice.

One of the things I've recently realized is the way this kind of information could confuse the global public. — Tate

You seem to be suggesting that the slowing of the circulation may trigger re-glaciation. but this looks to be backwards. Rather it is the melting sea ice that is reducing the salinity and thus the density of the water and so slowing the circulation. Re-glaciation would increase the salinity and thus strengthen the circulation.

You seem to be suggesting that the slowing of the circulation may trigger re-glaciation. but this looks to be backwards. Rather it is the melting sea ice that is reducing the salinity and thus the density of the water and so slowing the circulation. Re-glaciation would increase the salinity and thus strengthen the circulation. — unenlightened

But once reglaciation starts, it's self reinforcing, whether the thermohaline starts again or not. Ice sheets are considered by some scientists to be the most powerful force in the climate.

But once reglaciation starts, — Tate

It hasn't started though; on the contrary deglaciation is accelerating and it is the loss of ice that we are seeing. It is bizarre to suggest that something caused by loss of ice will cause an increase in ice. I don't say it is impossible, but it at the least demands a very detailed explanation of the mechanism, and how it is powerful enough to overcome the positive feedbacks of ice loss already discussed above.

But of the links you have provided so far, there is not one I have seen that remotely suggests that a new ice age is at all likely in the next few thousand years. Rather they all seem to suggest that a new ice age has already been prevented by the rise in CO2 levels.

It is bizarre to suggest that something caused by loss of ice will cause an increase in ice. — unenlightened

The shutdown of the thermohaline is caused by a loss of ice. It leads to an increase in ice. Scientists believe this has happened multiple times in the past. I think it makes more sense if you consider the wider context: that we're in a large scale ice age, stuck here by ocean currents that maintain deep water that never sees the light of day. Does that make sense?

don't say it is impossible, but it at the least demands a very detailed explanation of the mechanism, and how it is powerful enough to overcome the positive feedbacks of ice loss already discussed above. — unenlightened

Shutdown of the thermohaline is proposed as the cause of the Young Dryas. Do you want to look at whether anybody has tried to model that?

But of the links you have provided so far, there is not one I have seen that remotely suggests that a new ice age is at all likely in the next few thousand years. — unenlightened

That's not true. There are a couple of articles that propose thermohaline shutdown as the trigger for reglaciation during the 100,000 year cycle. I posted one of them.

It's a remote suggestion.

Rather they all seem to suggest that a new ice age has already been prevented by the rise in CO2 levels. — unenlightened

That's just the one that says the Anthropocene started 6000 years ago. That's a cool one.

He's saying we've already passed one trigger point.

There are a couple of articles that propose thermohaline shutdown as the trigger for reglaciation during the 100,000 year cycle. I posted one of them. — Tate

I haven't seen them, and I just looked back over the last couple of pages and still couldn't see any links I hadn't followed.

I'd really like to see where scientists are saying this:

The shutdown of the thermohaline is caused by a loss of ice. It leads to an increase in ice. — Tate

Looking myself I have found this:

Many of the climate changes related to the Younger Dryas were likely a response to increased freshwater discharge to the North Atlantic and the attendant reduction in Atlantic meridional overturning strength. Although multiple freshwater forcing hypotheses have been proposed, the existing terrestrial and marine records indicate that the northward retreat of the southern margin of the Laurentide Ice Sheet from the Great Lakes caused a routing of freshwater from the western Canadian Plains from the Mississippi River to the St. Lawrence River, with the increased freshwater discharge to the North Atlantic slowing ocean circulation and ultimately causing the Younger Dryas.

https://www.sciencedirect.com/topics/earth-and-planetary-sciences/younger-dryas

But that is a very different scenario, where the melting of land ice causes the growth of polar ice. Much harder to envisage the loss of polar sea ice causing an increase in polar ice.

It's slowing down now. here

I'm not sure what you're saying.

Did you want to explore the articles that say the slowing of the thermohaline might be the trigger for reglaciation?

I posted about why the previous explanation, which has been primary to long range modeling up till now, has been called into question. Did you see that post?

It's slowing down now. — Tate

I know it (ocean circulation) is slowing down. I expect it to slow down because polar ice is melting and lowering the salt, and thus density of the polar waters, so they don't sink (see your own link that I quoted above). I do not see how a slowdown caused by the melting of polar ice can result in increasing polar ice. I am looking for links that support your claims, and not finding any.

I do not see how a slowdown caused by the melting of polar ice can result in increasing polar ice. I am looking for links that support your claims, and not finding any. — unenlightened

A slow down or shutdown will be associated with a reduction in atmospheric CO2, resulting in cooling. But what's becoming apparent is that there isn't one magic bullet that initiates reglaciation. It happens when a number of factors are all in alignment: orbital forcing, precessional forcing (the Milankovitch cycle), and more broadly, just the fact that the climate is prone to glaciation for the last couple of million years.

Read this article, exploring the possibility that the THC (thermohaline circulation) is responsible for longer and shorter term changes in climate. It also talks about the debate about how the Younger Dryas actually started.

Here

And look at this one.

Thanks for engaging. I appreciate it.

A weak thermohaline circulation means less chance for surface and deep waters to mix, which facilitates reduced CO2 levels and hence further cooling.

Your first article makes this claim, but does not explain it. On the face of it, one would expect vigorous stirring to facilitate absorption of CO2 from the atmosphere. and lack of circulation to impede it. Any explanation?

The second link is not accessible to the Institute for Retired Busybodies, unfortunately.

Meanwhile, I have this:

Global warming can affect the THC in two ways: surface warming and surface freshening, both reducing the density of high-latitude surface waters and thus inhibiting deep water formation. [25] was the first to warn that this could lead to a breakdown of the THC and to abrupt climate change. Subsequently, [26, 27] showed that this could indeed occur for strong global warming (i.e., for a quadrupling, but not for a doubling of CO2). In these scenarios there was no surface cooling, as the high CO2 levels more than compensated for the reduced ocean heat transport. The possibility of a real cooling (both a relative cooling, i.e. a drop back to roughly pre-industrial temperatures after an initial warming phase, and in the longer run an absolute cooling below preindustrial values) as a result of anthropogenic warming was first demonstrated in a sensitivity study by [20]. Significant absolute cooling can arise after CO2 levels decline, but the THC remains switched off after its collapse is triggered in a rapid warming phase.
A THC collapse is now widely discussed as one of a number of "low probability - high impact" risks associated with global warming. More likely than a breakdown of the THC, which only occurs in very pessimistic scenarios, is a weakening of the THC by 20-50%, as simulated by many coupled climate models ([28]).

http://www.pik-potsdam.de/~stefan/thc_fact_sheet.html

All in all, the more I find out, the more the whole affair looks like humanity as a mad scientist in the process of blowing up his laboratory and speculating about whether he will be roasted or frozen or both.

Even if the thermohaline circulation would shut down, this would result in relatively local climate change limited to eastern North America and Western Europe and would result (as far as we understand) to lower temperatures.

Source?

Ex cathedra claims are being discounted in this thread.