The tipping point of the Atlantic overturning circulation

[knocker]

 

[Downburst]

I watched this, on 1.5 speed. Did take some notes to follow up. We need these studies prioritised and I do hope it gets the attention it needs, talk about understatement. Anyone else worried as to what the hell is happening here and why this isn't get attention?

[raz.org.rain]

On 14/11/2023 at 15:54, Downburst said:

I watched this, on 1.5 speed. Did take some notes to follow up. We need these studies prioritised and I do hope it gets the attention it needs, talk about understatement. Anyone else worried as to what the hell is happening here and why this isn't get attention?

It's a concerning situation, I do believe there's a great deal of misunderstanding as to the impacts of a collapse event. The widespread cooling trope is often pushed as the outcome with people referencing The Day After Tomorrow and pretending it's factually correct. People rarely seem to reference the fact that a collapse would result in much hotter and drier summers across Europe, with hypothetically colder winters. I say hypothetical, as we've got anthropogenic warming thrown into the mix. I don't believe that temperature will be the concern with a collapse event, it's the huge drop in precipitation across the globe and particularly in Europe.

[richie3846]

On 14/11/2023 at 14:04, knocker said:

 

I disagree with the way this professor chooses his words. The word 'confirmed' in the same sentence as 'climate model' is not what I expect from a professor. A single climate model doesn't confirm anything, it gives us more information to make assessments, and his poor choice of words here suggests this is some sort of fact now. I suggest he may be doing this for his ego, because frankly, professors don't need to feed this sort of soundbite through a twitter account, for likes. 

[knocker]

I am constantly reminded that on occasion it is very silly of me to ignore the advice of some time ago that my posting on this site is not welcome.

[alexisj9]

11 minutes ago, knocker said:

I am constantly reminded that on occasion it is very silly of me to ignore the advice of some time ago that my posting on this site is not welcome.

I don't think that what was meant, unless of course things have been deleted. I thank you for posting this thread.

[alexisj9]

2 hours ago, richie3846 said:

I disagree with the way this professor chooses his words. The word 'confirmed' in the same sentence as 'climate model' is not what I expect from a professor. A single climate model doesn't confirm anything, it gives us more information to make assessments, and his poor choice of words here suggests this is some sort of fact now. I suggest he may be doing this for his ego, because frankly, professors don't need to feed this sort of soundbite through a twitter account, for likes. 

Having read the rest while click on that tweet, it's more like a model confirming finding from other models, wording is correct.

[richie3846]

5 hours ago, alexisj9 said:

Having read the rest while click on that tweet, it's more like a model confirming finding from other models, wording is correct.

I still disagree with the word confirmed in this context. Confirm usually indicates fact, not projection. 

[Firefly2005]

Really interesting - thanks! 

[raz.org.rain]

7 hours ago, alexisj9 said:

Having read the rest while click on that tweet, it's more like a model confirming finding from other models, wording is correct.

There's a lot of disagreement when it comes to the subject of the AMOC. In fact, there's not even a universal agreement as to whether the modelling software used to reconstruct its behaviour is entirely accurate. 

[alexisj9]

6 hours ago, razorgrain said:

There's a lot of disagreement when it comes to the subject of the AMOC. In fact, there's not even a universal agreement as to whether the modelling software used to reconstruct its behaviour is entirely accurate. 

Of course there is, anything from whether it will happen to what the effects will be if it does. However one thing everyone should agree on, because it's not just modelled, but actually happening now, is the gulf stream has slowed down.

[raz.org.rain]

14 hours ago, alexisj9 said:

Of course there is, anything from whether it will happen to what the effects will be if it does. However one thing everyone should agree on, because it's not just modelled, but actually happening now, is the gulf stream has slowed down.

It has slowed down, the curious detail there is that we've seen accelerated warming as a direct result. The past few years have seen some intense summer heat domes form in response to the Atlantic warming hole. The jet stream buckles and drags in hot air masses from Africa and causes them to stagnate for long periods of time. This cool-ocean-warm-summer effect doesn't get discussed very often.

[WYorksWeather]

There are three main things that need to be understood, as I understand the latest science (happy to be corrected), about when / how an AMOC collapse would happen.

Firstly, there's the trigger point - at what temperature does the process of AMOC collapse start. There is an argument to be made that since the AMOC is already slowing down, we're at the start of that process already, but other scientists still think this could be an initial fall that is self-limiting, not a collapse.

The second thing is the tipping point - at what point does the collapse become unstoppable, in other words when do we reach the point that if all emissions ceased tomorrow, the AMOC will still collapse completely?

And the third area of interest is what does that collapse process look like. Is it a slow wind down over many decades, or could it happen very quickly (which given the massive change in regional climate, I would define very quickly as within 10 years of the tipping point being reached).

In terms of adaptation, that's the other thing that isn't clear. My guess would be that we would have more of a seasonal temperature range, perhaps closer to a more continental climate. Something like regular high 30s to 40C in summer, and much more cold and snow in winter. Which would be tricky, as we'd need both more snow ploughs, and home air conditioning!

[Chesil View]

From my admittedly limited reading on the subject over the years.  This is not really that new. I have read before of a scenario whereby CC continues on its warming global trajectory but that northwest Europe gains a more continental or extreme climate at both ends of the scale. So perhaps more heatwaves like or perhaps warmer than 2022 but also an increase in colder snowier winters to balance the equation somewhat. If the tipping point has indeed been reached and collapse is incoming it certainly makes for some interesting scenarios.

[Sky Full]

52 minutes ago, razorgrain said:

It has slowed down, the curious detail there is that we've seen accelerated warming as a direct result. ………

Excuse my ignorance and my laziness in not searching for the answer elsewhere, but can anyone explain how this slow-down is measured and how does it manifest itself in real terms?  

[raz.org.rain]

5 minutes ago, Sky Full said:

Excuse my ignorance and my laziness in not searching for the answer elsewhere, but can anyone explain how this slow-down is measured and how does it manifest itself in real terms?  

Admittedly I'm not entirely sure of the process myself but I believe it involves using buoys that are placed off the coast of Florida to measure the temperature variation in the ocean. I'd assume that a similar process is used throughout the North Atlantic. I remember a quote from a few years ago that "(paraphrased) the AMOC/Gulf Stream is a set of mathematical equations and outputs", the gist being that it's largely a computed theory using data input models to give an impression of what's happening. I believe this is where a lot of the disagreement comes from, because the method of data collection and data input differs depending on who is observing it at the time.

[raz.org.rain]

9 minutes ago, Chesil View said:

From my admittedly limited reading on the subject over the years.  This is not really that new. I have read before of a scenario whereby CC continues on its warming global trajectory but that northwest Europe gains a more continental or extreme climate at both ends of the scale. So perhaps more heatwaves like or perhaps warmer than 2022 but also an increase in colder snowier winters to balance the equation somewhat. If the tipping point has indeed been reached and collapse is incoming it certainly makes for some interesting scenarios.

That would be my assumption, as the AMOC is a moderating factor more than it is a warming factor. It's largely responsible for the lack of extremes found in northwestern Europe. Climate change throws a spanner in the works because it directly impacts the cooling mechanisms required for extremes in cold to form, so the likelihood of dramatic extremes of cold are very unlikely when compared to the potential for extremes in heat.

[WYorksWeather]

44 minutes ago, razorgrain said:

That would be my assumption, as the AMOC is a moderating factor more than it is a warming factor. It's largely responsible for the lack of extremes found in northwestern Europe. Climate change throws a spanner in the works because it directly impacts the cooling mechanisms required for extremes in cold to form, so the likelihood of dramatic extremes of cold are very unlikely when compared to the potential for extremes in heat.

Another key impact is a drying trend. An AMOC collapse would reduce rainfall during the growing season by 123mm according to one study (see this article for an accessible summary), and we'd lose most of our arable land without massive irrigation schemes, which the study concludes would be uneconomic in any case. That'd probably be much harder to adapt to than the temperature change, and we'd be even more reliant on food imports than we are already.

[raz.org.rain]

43 minutes ago, WYorksWeather said:

Another key impact is a drying trend. An AMOC collapse would reduce rainfall during the growing season by 123mm according to one study (see this article for an accessible summary), and we'd lose most of our arable land without massive irrigation schemes, which the study concludes would be uneconomic in any case. That'd probably be much harder to adapt to than the temperature change, and we'd be even more reliant on food imports than we are already.

That article makes a good point about precipitation change, although I don't agree with their conclusions on cooling. The dramatic drop in precipitation would actually cause a warming effect during the summer months, as the AMOC's contribution to precipitation actually has a cooling effect across most of western and parts of Northern Europe. When we factor in this abrupt drop in precipitation with the much hotter summers, widespread desertification becomes a much greater risk, which itself would feed into amplified warming across the continent. Although I'd concede that parts of Northern Europe **might** observe a cooling trend in both winter and summer, I don't think it's at all a viable outcome for lower latitudes (below 60°).

[WYorksWeather]

12 minutes ago, razorgrain said:

That article makes a good point about precipitation change, although I don't agree with their conclusions on cooling. The dramatic drop in precipitation would actually cause a warming effect during the summer months, as the AMOC's contribution to precipitation actually has a cooling effect across most of western and parts of Northern Europe. When we factor in this abrupt drop in precipitation with the much hotter summers, widespread desertification becomes a much greater risk, which itself would feed into amplified warming across the continent. Although I'd concede that parts of Northern Europe **might** observe a cooling trend in both winter and summer, I don't think it's at all a viable outcome for lower latitudes (below 60°).

To be fair, the article does predict as such - Scotland cools the most, whereas for southern parts of the UK the change is minimal compared to today's conditions. Just shifted a little further south from your expectations - would suggest the break even is closer to low 50s latitude than 60 degrees north.

I would also say that even an overall cooling doesn't necessarily mean cooling in summer. If summer temperatures rose 3C but winter temperatures fell 5C that would still be an overall fall in temperature.

[raz.org.rain]

13 minutes ago, WYorksWeather said:

To be fair, the article does predict as such - Scotland cools the most, whereas for southern parts of the UK the change is minimal compared to today's conditions. Just shifted a little further south from your expectations - would suggest the break even is closer to low 50s latitude than 60 degrees north.

I would also say that even an overall cooling doesn't necessarily mean cooling in summer. If summer temperatures rose 3C but winter temperatures fell 5C that would still be an overall fall in temperature.

That seems more likely, the annual cooling trend being greater than the warming trend. It wouldn't take much warming for our climate to be notably hot, I'd imagine the summer climate would resemble something close to what south-central France currently has, winters could possibly be Baltic.

[WYorksWeather]

13 minutes ago, razorgrain said:

That seems more likely, the annual cooling trend being greater than the warming trend. It wouldn't take much warming for our climate to be notably hot, I'd imagine the summer climate would resemble something close to what south-central France currently has, winters could possibly be Baltic.

Unfortunately I can't access the actual paper, it'd be interesting to check what they are actually forecasting.

You're right by the way - not far south of France, but certainly central-southern France would be possible. Lyon's summer temperatures are only around 4C higher than ours, so it wouldn't surprise me if London got quite close to that, but Scotland didn't warm much in summer if at all and had absolutely frigid winters.

[raz.org.rain]

Here's an interesting study released today, which discusses the link between the AMOC and the heat balance in the atmosphere. They theorise that a slower or absent AMOC actually results in more heat being present in the atmosphere, due to not being absorbed into and distributed by the currents. Hypothetically this resulted in events such as the Little Ice Age not being as cold as they may otherwise have been (although the LIA is a complex subject, with dozens of factors contributing to cooling such as volcanic eruptions and rapid population decline in response to disease and famine).

This really does raise the question of what the implications would be in the current period, as the atmosphere is choked with warming gases. If the currents slow down and there's less distribution, then according to this study, that heat gets released back into the atmosphere and has a warming effect on the climates affected by the AMOC.

Edited November 18, 2023 by razorgrain

[alexisj9]

On 17/11/2023 at 17:53, WYorksWeather said:

There are three main things that need to be understood, as I understand the latest science (happy to be corrected), about when / how an AMOC collapse would happen.

Firstly, there's the trigger point - at what temperature does the process of AMOC collapse start. There is an argument to be made that since the AMOC is already slowing down, we're at the start of that process already, but other scientists still think this could be an initial fall that is self-limiting, not a collapse.

The second thing is the tipping point - at what point does the collapse become unstoppable, in other words when do we reach the point that if all emissions ceased tomorrow, the AMOC will still collapse completely?

And the third area of interest is what does that collapse process look like. Is it a slow wind down over many decades, or could it happen very quickly (which given the massive change in regional climate, I would define very quickly as within 10 years of the tipping point being reached).

In terms of adaptation, that's the other thing that isn't clear. My guess would be that we would have more of a seasonal temperature range, perhaps closer to a more continental climate. Something like regular high 30s to 40C in summer, and much more cold and snow in winter. Which would be tricky, as we'd need both more snow ploughs, and home air conditioning!

The way I see it, for now, warm water heading north has slowed, which would mean less cold heading south, probably accounts for the anomalous warm waters we've been having. Also  warmth heading north at a slower rate,  has allowed for quick ice formation in the poll this year.

Looking at what's happening now, I would expect more severe winters once things slow down further, not sure what a full stop would look like, summers will be dependent as usual on where  the weather is coming from, but heat domes are not going to disappear,  may even get stuck over one area for longer perhaps.

Edited November 18, 2023 by alexisj9

[WYorksWeather]

1 hour ago, alexisj9 said:

The way I see it, for now, warm water heading north has slowed, which would mean less cold heading south, probably accounts for the anomalous warm waters we've been having. Also  warmth heading north at a slower rate,  has allowed for quick ice formation in the poll this year.

Looking at what's happening now, I would expect more severe winters once things slow down further, not sure what a full stop would look like, summers will be dependent as usual on where  the weather is coming from, but heat domes are not going to disappear,  may even get stuck over one area for longer perhaps.

A lot will also depend on how much warming we get. Probably the coldest scenario would be warming just enough to shut down the AMOC. Obviously if we keep warming beyond that point it'll balance out any cooling. E.g. I can't imagine if we got a worst case of 4-5C warming (very unlikely scenario) that we'd be cooler than today, even if the AMOC did shut down. Of course, at global warming of 4-5C in this century, that'd be the least of our worries...