When will the Arctic go ice free? 2023

[RoxTheGeologist]

I figure it's not down so much to temperature - I know - Ice melting. It will be down to how heat is transferred to the poles from the tropics. The heat transfer in the ocean doesn't impact the ice melting - except in the Barents Sea, where the shelf break clearly defines the ice edge. There is not enough insolation to melt the ice above 85 degrees. The Sun's angle is too low to make up for the emissive loss.  Heat is not transferred from the ocean because of the freshwater lens that sits over the Arctic - and that is not going away with the volume of rivers draining into the Arctic.

So - we have to have more heat transferred to the poles through the atmosphere - I think that will happen as the AMOC slows. As the energy transfer through the oceans decreases, the amount of heat transfer through the atmosphere will increase. But - wont the ice cap grow more as the AMOC slows? I'd expect to see an expansion in the area covered by sea ice before we see its final demise.




 

[binntho]

I do not understand this infatuation with linear trends.  The relationship between two variables will be dictated by the science behind the effect.  The relationship could be linear, exponential, logarithmic, some other, or none at all.  A linear relationship should by no means be considered the default trend.

There are vastly more than two variables at play, and the chances of there being a linear rate of change in a complex system are very low. So there is no "infatuation" with linear trends - they are inherently extremely unlikely, particularly in the long run.

However, the chances of a complex system following binomial or logarithmic trends, let alone trinomial or higher factors, is even less likely than following a linear trend.

Complex systems do not follow mathematically neat trends. Trying to find them is futile. We are not seeing any linear trends in the Arctic today, but nor are we seeing any other trends that can be expressed in neat mathematical formulae.

The real-world data that we are dealing with seems to be following something close to a linear trend when it comes to statistical correlation. But what about physical causality? The ice is melting due to an increase in temperature, and during the 43 years that we are typically looking at, global temperatures have also followed a near-linear trend.

If we were to plot the two (e.g. global annual average temperatures v.s. annual average sea ice extent) we are very likely to see something very close to a linear correlation. This however does not imply causality. There is no reason to think that there is a linear causal relationship between the two, except contingently and temporarily under certain circumstances which may have governed the last 40 years, or perhaps we are not looking at a large enough timeframe.

But trying to find logarithmic or polynomial trends without a b****y good explanation of the physics that might be behind such a trend is never going to work. And when it comes to the Arctic we are very far away from being able to explain the physics behind a linear trend, let alone a polynomial one!

[The Walrus]

I do not understand this infatuation with linear trends.  The relationship between two variables will be dictated by the science behind the effect.  The relationship could be linear, exponential, logarithmic, some other, or none at all.  A linear relationship should by no means be considered the default trend.

There are vastly more than two variables at play, and the chances of there being a linear rate of change in a complex system are very low. So there is no "infatuation" with linear trends - they are inherently extremely unlikely, particularly in the long run.

However, the chances of a complex system following binomial or logarithmic trends, let alone trinomial or higher factors, is even less likely than following a linear trend.

Complex systems do not follow mathematically neat trends. Trying to find them is futile. We are not seeing any linear trends in the Arctic today, but nor are we seeing any other trends that can be expressed in neat mathematical formulae.

The real-world data that we are dealing with seems to be following something close to a linear trend when it comes to statistical correlation. But what about physical causality? The ice is melting due to an increase in temperature, and during the 43 years that we are typically looking at, global temperatures have also followed a near-linear trend.

If we were to plot the two (e.g. global annual average temperatures v.s. annual average sea ice extent) we are very likely to see something very close to a linear correlation. This however does not imply causality. There is no reason to think that there is a linear causal relationship between the two, except contingently and temporarily under certain circumstances which may have governed the last 40 years, or perhaps we are not looking at a large enough timeframe.

But trying to find logarithmic or polynomial trends without a b****y good explanation of the physics that might be behind such a trend is never going to work. And when it comes to the Arctic we are very far away from being able to explain the physics behind a linear trend, let alone a polynomial one!

On one side, you state that a linear trend is "extremely unlikely," and "we are not seeing any linear trends in the Arctic."  Then on the other side of your mouth, you say, "the ice is melting ... following a near-linear trend."  Which is it?

As many have shown, neither Arctic temperatures nor Arctic sea ice have followed a linear trend for more than a few years out of the data record.  Clinging to this short correlation seems to me to be an infatuation.

[The Walrus]

Summer temperature where sea ice is found is pegged to the melting points of snow and sea ice. When more energy is added, temperatures stay the same but the ice thins, with extent often remaining the same for a long while in regions where ice has a near-uniform thckness.
Where ice has already melted out, temperatures can climb commensurately with added energy. (This has been explained often and in detail yet still seems to escape some posters).
From the above it follows that a decline in summer extent will correlate with higher summer temps, and not necessarily the other way around.
It also follows that typical thickness and total volume are much better predictors of future sea ice behavior than the variable some posters seem to be fixated on, that of extent.

On a smaller scale, this is what occurs on lakes.  As the temperature warms, the ice thins, decreasing thickness (and consequently volume).  The extent remains constant, until the ice becomes too thin, and poof, all the ice disappears quickly.

The Arctic is different.  As temperatures increase, thick ice in the center begins to thin, but thin ice around the edges begins to melt.  Consequently, extent decreases along with thickness and volume (volume faster as a combination of both thickness and extent).

Not sure that thickness or volume are better indicators.  Perhaps if we could measure them more accurately, they might be.  However, this is the ice-free thread, which is based on extent (there are other threads for volume).

[Albert56]

Please add option "never"

[oren]

Welcome, Albert.
The poll is old, maybe those who open the next one will take up your suggestion.

[kassy]

2100+ is that.

In reality never is not an option.
And we will get to see it. If you don´t believe so any value over 2100 is never.

[RoxTheGeologist]

What happens to the Sea Ice when the AMOC slows?

Does the extent of sea ice increase? I would say yes
Heat transfer from the Equator to the poles will be carried by atmospheric water rather than the oceans.

My guess is we will see sea ice increase, and only when we see heat transfer in the atmosphere (trending to an equitable climate) will sea ice in the Arctic disappear. There isn't enough insolation to melt the ice, and the freshwater lens is replenished by river water. The only way there can be enough heat transferred (to make up for the losses in the winter) is if the atmosphere is warmer and wetter.

[binntho]

What happens to the Sea Ice when the AMOC slows?

The AMOC is not (yet) slowing down - and may not slow down at all. Various scientists have predicted a slow-down but all the predictions I have seen are based on highly unrealistic scenarios. And the North Atlantic Drift, the small off-shoot from the Gulf Stream that actually reaches the Arctic, has been strengthening and not weakening.

Does the extent of sea ice increase? I would say yes
Heat transfer from the Equator to the poles will be carried by atmospheric water rather than the oceans.

My guess is we will see sea ice increase, and only when we see heat transfer in the atmosphere (trending to an equitable climate) will sea ice in the Arctic disappear. There isn't enough insolation to melt the ice, and the freshwater lens is replenished by river water. The only way there can be enough heat transferred (to make up for the losses in the winter) is if the atmosphere is warmer and wetter.

The last interglacial (called the Eemian interglacial) is a good comparison. It lasted about 10.000 years and was warmer than our current interglacial (although we may have matched that already, or at least soon will). The Greenland glacier was much smaller than today and hippotami frolicked in the Thames.

Most agree that the Arctic ocean was seasonally ice free during the Eemian (although I have been unable to find a direct reference - Wikipedia is going downhill, and all the likely papers found by Google had either disappeared or were behind paywalls).

An interesting feature of the Eemian seems to be that the North Atlantic Drift may have been severely weakened or even stopped altogether. A likely cause is that the Saalian glaciation, which preceded the Eemian interglacial, was much bigger than the Weichselian glaciation preceding our own interglacial. Large amounts of meltwater from North America and Siberia took a long time to drain from the Arctic, possibly stopping the North Atlantic Drift from forming. At the same time, the Atlantic seems to have been a lot warmer. See "Warm climate -- cold Arctic? The Eemian is a poor analogue for current climate change"

The main point perhaps is that it does not require an equitable climate for the Arctic Ocean to be seasonally ice-free. And that current temperatures are probably sufficient, or at least very close to, what is needed for a seasonal ice-free Arctic Ocean.

[Richard Rathbone]

What happens to the Sea Ice when the AMOC slows?

The AMOC is not (yet) slowing down - and may not slow down at all. Various scientists have predicted a slow-down but all the predictions I have seen are based on highly unrealistic scenarios. And the North Atlantic Drift, the small off-shoot from the Gulf Stream that actually reaches the Arctic, has been strengthening and not weakening.

https://www.realclimate.org/index.php/archives/2024/02/new-study-suggests-the-atlantic-overturning-circulation-amoc-is-on-tipping-course/

Realclimate discussion of “Physics-based early warning signal shows that AMOC is on tipping course.”  by van Westen et al.

It confirms that the AMOC has a tipping point beyond which it breaks down if the northern Atlantic Ocean is diluted with freshwater (by increasing rainfall, river runoff and meltwater), thus reducing its salinity and density.

It confirms by using observational data that the Atlantic is “on tipping course”, i.e. moving towards this tipping point. The billion-dollar question is: how far away is this tipping point?

The new study confirms past concerns that climate models systematically overestimate the stability of the AMOC. About the crucial AMOC freshwater transport in models, they point out that most models don’t get it right: “This is not in agreement with observations, which is a well-known bias in CMIP phase 3 (38), phase 5 (21), and phase 6 (37) models.” Most models even have the wrong sign of this important diagnostic, which determines whether the feedback on Atlantic salinity is stabilising or destabilising, and this model bias is a key reason why in my view the IPCC has so far underestimated the risk of an AMOC collapse by relying on these biased climate models.

[Sublime_Rime]

Indeed the Realclimate article covers two groups independently coming to similar conclusions regarding the possibility of tipping this century, as early as mid-century. I am curious what you mean by "unrealistic scenarios" Binntho? It seems like both of these examples are assuming middle of the road or currently policy scenarios.