Abrupt sea ice loss

[Cid_Yama]

when analyzing seasonal differences of sea ice retreat, Eisenman et al. (2011, p. 5332) found that “some GCMs become seasonally ice free during the 1900–2100 simulation period. This leads to winter ice cover retreating faster than summer ice cover after the latter reaches zero.” Moreover, abrupt Arctic winter sea ice loss was recently detected in model simulations from phase 5 of the Coupled Model Intercomparison Project (CMIP5) (Drijfhout et al. 2015). CMIP5 provides results from current comprehensive climate models and allows us to compare their response to anthropogenic forcing (Taylor et al. 2012).

The most striking winter sea ice decline occurs in the Earth system model of the Max Planck Institute for Meteorology, MPI-ESM (Giorgetta et al. 2013; Notz et al. 2013), where an ice area of several million square kilometers disappears within only a few years (Fig. 1). Winton (2006, 2008) showed that in the version of MPI-ESM that he analyzed, this transition is accompanied by an increased ice–albedo feedback, concluding that this feedback is responsible for the high rate of winter sea ice loss. The ice–albedo feedback plays a role for winter sea ice because the seasonal cycle of sea ice area lags the insolation cycle by approximately three months. Thus, ice volume and area are near their annual maximum when the sun rises in March. Li et al. (2013) further speculated that a convective cloud feedback proposed by Abbot and Tziperman (2008) could also play a role for the winter sea ice loss in MPI-ESM: In an Arctic Ocean without winter sea ice, the warmer and wetter conditions could trigger the formation of convective clouds, resulting in enhanced downwelling longwave radiation at the surface and reduced cooling to space. This warming due to the cloud radiative effect would then help to keep the Arctic ice-free.

In this study we propose a different explanation for the abrupt sea ice loss in MPI-ESM that also explains the sensitive Arctic winter sea ice area in the other models: the freezing temperature imposes a threshold for the formation of winter ice. Where the ocean no longer cools to the freezing temperature in winter, sea ice can essentially disappear from one winter to the next. If the basinwide conditions are spatially homogeneous enough, this mechanism can result in a rapid sea ice loss in a large area.

In the following, we first show that Arctic winter sea ice area is more sensitive to warming than summer sea ice area in CMIP5 models. We then outline the essence of our explanation using an idealized ice-thickness distribution (ITD) model that resolves many thickness classes in contrast to the slab model by Eisenman and Wettlaufer (2009). To show that the mechanism is indeed active in comprehensive climate models, we show consistent sea ice area and thickness changes in these models. Thereafter, we present additional simulations with MPI-ESM, showing that neither surface albedo nor radiative cloud feedbacks can explain the abrupt sea ice loss in this model. Furthermore, we demonstrate with a simple box model, capturing the essence of the ice-area parameterization in MPI-ESM, that our thermodynamic argument is sufficient to explain the abrupt ice loss. We finally argue why other feedbacks are unlikely to play a dominant role also in other complex climate models and discuss important differences between the Arctic and the Southern Hemisphere.

https://journals.ametsoc.org/doi/10.1175/JCLI-D-15-0466.1

[Dharma Rupa]

While I'm a bit skeptical of the models (until I see reasonable stats on skill), I have long held that when the Arctic decides to melt-out it won't matter what time of year it is.

Comes down to Ocean Heat and the fact that H2O is the primary greenhouse gas -- I guess that means it all comes down to water.  CO2 is the trigger, not the bullet.

[Cid_Yama]

While Screen et al. 2011 focused on the number of cyclones as a possible factor to explain the September variability, this study looks to see individual cyclone’s effects on abrupt sea ice loss as a possible factor of the September variability. For example, Simmonds et al. 2012 noted that a single cyclone was associated with a large reduction in SIE during the summer of 2012. This cyclone, now known as the “Great Arctic Cyclone,” likely contributed to the 2012 all-time minimum in Arctic SIE. Furthermore, Ogi et al. 2009 noted that wind forcing on sea ice accounted for a 50% variance of September year-to-year SIE, while Rigor et al. 2002 showed that the thin sea ice during the summer over the Arctic is particularly vulnerable to atmospheric winds. Motivated by the observations that a cyclone can have an impact on SIE, this study aims to determine whether individual synoptic events are generally a significant contributor to abrupt sea ice loss.

link

[Sciguy]

It's important to read how they run the simulations in the models.  Here's what they did in the paper above:

The loss of Arctic sea ice during the whole year that we examine here only occurs under the large radiative forcing of the RCP8.5 simulations. In these simulations, the CO2 concentration is prescribed and shows an accelerating increase until the year 2100 (implying a radiative forcing from well-mixed greenhouse gases of 8.5 W m−2), followed by a stabilization period with a decelerating increase (Meinshausen et al. 2011). In the year 2250, the CO2 concentration reaches its final level of almost 2000 ppm.

If we continue on a high emissions path as described by the paragraph above, loss of the winter Arctic sea ice will be the least of our worries.  Note that the current goals of international agreements are to stabilize concentrations at 450 ppm and that some organizations are work toward an eventual reduction to 350 ppm by studying ways to take CO2 out of the atmosphere and sequester it.

[Tor Bejnar]

CO2 is the trigger, not the bullet.

Nice slogan, and functionally true!

CO2 is causing the problems of Global Wierding.  What'll kill us is floods, heatwaves, fires, starvation (due to loss of food production caused by unseasonable/excessive rain/hail/freeze/thaw/drought) and poison ivy (it particularly likes increased CO2 - or at least make walking in my woods unpleasant).  Farmers have always had to contend with weather; now they have to attempt to contend with weather-gone-amok!

[Neven]

Cid_Yama, I've merged the two threads you opened and given them a more generic name.

[Dharma Rupa]

CO2 is the trigger, not the bullet.

Nice slogan, and functionally true!

CO2 is causing the problems of Global Wierding.  What'll kill us is floods, heatwaves, fires, starvation (due to loss of food production caused by unseasonable/excessive rain/hail/freeze/thaw/drought) and poison ivy (it particularly likes increased CO2 - or at least make walking in my woods unpleasant).  Farmers have always had to contend with weather; now they have to attempt to contend with weather-gone-amok!

I'll punt on the poison ivy, I don't react to it all that much.


I suspect that more people will suffer from global warming than will benefit, but I will note that the rise of the Kahns was probably due to a number of years of unusual rainfall in the Stepps allowing their horses to flourish.

[Daniel B.]

CO2 is the trigger, not the bullet.

Nice slogan, and functionally true!

CO2 is causing the problems of Global Wierding.  What'll kill us is floods, heatwaves, fires, starvation (due to loss of food production caused by unseasonable/excessive rain/hail/freeze/thaw/drought) and poison ivy (it particularly likes increased CO2 - or at least make walking in my woods unpleasant).  Farmers have always had to contend with weather; now they have to attempt to contend with weather-gone-amok!

I will take the wait and see attitude regarding the farmers.  To date, there has been a net benefit, due to increased rainfall and longer growing seasons.  If the rainfall increases dramatically, then that might lead to decreased output, but that might take a long time to reach.

[Archimid]

I will take the wait and see attitude regarding the farmers.  To date, there has been a net benefit, due to increased rainfall and longer growing seasons.  If the rainfall increases dramatically, then that might lead to decreased output, but that might take a long time to reach.

Daniel B. While yields for many grains and important crops are up you can't say climate change has been a net benefit. Most likely the gains are technological improvements surpassing climate related losses. It is likely that without climate change the gains would have been much greater.

[wili]

ummmm...this all seems pretty far off topic to the thread's title...but since it has gone this direction already, may I add:

https://www.politico.com/agenda/story/2017/09/13/food-nutrients-carbon-dioxide-000511

The great nutrient collapse

The atmosphere is literally changing the food we eat, for the worse. And almost nobody is paying attention.

[Daniel B.]

ummmm...this all seems pretty far off topic to the thread's title...but since it has gone this direction already, may I add:

https://www.politico.com/agenda/story/2017/09/13/food-nutrients-carbon-dioxide-000511

The great nutrient collapse

The atmosphere is literally changing the food we eat, for the worse. And almost nobody is paying attention.

Maybe one last OT, then I will cease.  That is all rather straight-forward, and not surprising.  Plant growth is determined by its limiting factor.  Increase that factor, and growth increases.  If that factor is water, sunlight, CO2, etc., then that will lead to increased carbohydrate production in the leaves and subsequently, fruit.  Unless nutrients are added to the soil, the uptake of these minerals will remain roughly the same (unless increased photosynthesis helps the plant pull in more), but be distributed over greater plant volume.  The caloric value of the food will increase as photosynthesis increases, but the mineral fraction will decrease.  A single plant will produce food with the overall same mineral content, but be distributed over more or larger fruits.  Not exactly junk food as the author contends.

[Tor Bejnar]

Severe drought conditions extend well into Kansas and Colorado. Close to half of the winter wheat in Kansas—the nation’s largest producer of the crop—was ranked in poor or very poor condition by the U.S. Department of Agriculture as of Sunday. “The wheat hasn’t gone downhill, it’s never been uphill,” farmer Jay Warner told the McPherson Sentinel.

yesterday's Weather Underground "Category 6" article

Of course, droughts have happened before, but with the abrupt sea ice loss we have experienced these past few decades [I was trained to think geologically], they're more common now (and strike more quickly).

I blame these OT comments to the change in thread title.  (But I might just be rationalizing.)

[Neven]

Maybe one last OT, then I will cease.  That is all rather straight-forward, and not surprising.  Plant growth is determined by its limiting factor.  Increase that factor, and growth increases.  If that factor is water, sunlight, CO2, etc., then that will lead to increased carbohydrate production in the leaves and subsequently, fruit.  Unless nutrients are added to the soil, the uptake of these minerals will remain roughly the same (unless increased photosynthesis helps the plant pull in more), but be distributed over greater plant volume.  The caloric value of the food will increase as photosynthesis increases, but the mineral fraction will decrease.  A single plant will produce food with the overall same mineral content, but be distributed over more or larger fruits.  Not exactly junk food as the author contends.

I guess you didn't read all the way to:

These experiments and others like them have shown scientists that plants change in important ways when they’re grown at elevated CO2 levels. Within the category of plants known as “C3”―which includes approximately 95 percent of plant species on earth, including ones we eat like wheat, rice, barley and potatoes―elevated CO2 has been shown to drive down important minerals like calcium, potassium, zinc and iron. The data we have, which look at how plants would respond to the kind of CO2 concentrations we may see in our lifetimes, show these important minerals drop by 8 percent, on average. The same conditions have been shown to drive down the protein content of C3 crops, in some cases significantly, with wheat and rice dropping 6 percent and 8 percent, respectively.

CO2 is plant food, like steroids are muscle food. Looks great, but is it healthy?

And while food production is up (by squeezing everything we can out of dead soil with the help of fossil fuels), food quality continues its steady decline. And we wonder why people are getting sicker and dumber.

Thanks, wili, that was the best OT I've read in a while. 

[Daniel B.]

Maybe one last OT, then I will cease.  That is all rather straight-forward, and not surprising.  Plant growth is determined by its limiting factor.  Increase that factor, and growth increases.  If that factor is water, sunlight, CO2, etc., then that will lead to increased carbohydrate production in the leaves and subsequently, fruit.  Unless nutrients are added to the soil, the uptake of these minerals will remain roughly the same (unless increased photosynthesis helps the plant pull in more), but be distributed over greater plant volume.  The caloric value of the food will increase as photosynthesis increases, but the mineral fraction will decrease.  A single plant will produce food with the overall same mineral content, but be distributed over more or larger fruits.  Not exactly junk food as the author contends.

I guess you didn't read all the way to:

These experiments and others like them have shown scientists that plants change in important ways when they’re grown at elevated CO2 levels. Within the category of plants known as “C3”―which includes approximately 95 percent of plant species on earth, including ones we eat like wheat, rice, barley and potatoes―elevated CO2 has been shown to drive down important minerals like calcium, potassium, zinc and iron. The data we have, which look at how plants would respond to the kind of CO2 concentrations we may see in our lifetimes, show these important minerals drop by 8 percent, on average. The same conditions have been shown to drive down the protein content of C3 crops, in some cases significantly, with wheat and rice dropping 6 percent and 8 percent, respectively.

CO2 is plant food, like steroids are muscle food. Looks great, but is it healthy?

And while food production is up (by squeezing everything we can out of dead soil with the help of fossil fuels), food quality continues its steady decline. And we wonder why people are getting sicker and dumber.

Thanks, wili, that was the best OT I've read in a while. 

Actually I did read the entire thing.  Hence my comment about increased caloric content, but decreased mineral content.  Simple mathematics; if you increase the total volume, but keep a particular element constant, its percentage must decrease.  The added volume is still nutritious foodstuffs, which is the primary concern in undernourished countries.

[wili]

(Is it time to split these increasingly absurd and off topic postings into another thread? Or should we all just drop it?)

The extra carbon adds starches and sugars and probably some fiber, not 'nutritious stuff.' I most of the world now, including most of the world's poor areas, obesity...getting to much of sugars and starches and often not enough of real nutrients...is as major an issue as is the malnutrition that comes from not getting enough calories.

Once considered a problem only of high-income countries, obesity rates are rising worldwide and affecting both the developed and developing world. These increases have been felt most dramatically in urban settings...

https://en.wikipedia.org/wiki/Obesity

[Neven]

Actually I did read the entire thing.  Hence my comment about increased caloric content, but decreased mineral content.  Simple mathematics; if you increase the total volume, but keep a particular element constant, its percentage must decrease.  The added volume is still nutritious foodstuffs, which is the primary concern in undernourished countries.

I see what you mean now. Maybe they could've explained it better. The way I understood it, less nutrients get taken up because the 'space' is taken up by more carbohydrates. If I've understood you correctly, you say that the plant grows bigger (volume is increased), while taking up the same amount of nutrients.

I've just read a book about how plants interact with soil life. They get their minerals through 'exudates' which they exchange with bacteria and fungi. I don't know how that would change if the plant contains more carbohydrates because of increased atmospheric CO2.

If the science is correct, this could seriously affect health, on top of the mineral depletion that has been taken place for a while now. In that sense, it has the same effect as junk food.

[Neven]

(Is it time to split these increasingly absurd and off topic postings into another thread? Or should we all just drop it?)

We should drop it, or continue here.

Apparently, the subject of this thread doesn't attract enough comments on its own. Of course, it's been discussed indirectly elsewhere.

[Daniel B.]

(Is it time to split these increasingly absurd and off topic postings into another thread? Or should we all just drop it?)

We should drop it, or continue here.

Apparently, the subject of this thread doesn't attract enough comments on its own. Of course, it's been discussed indirectly elsewhere.

Agreed.  But at least we seem to understand each other now.  Sorry if my previous posts were unclear.

[Dharma Rupa]

OK...Given the topic, I have a question.  Is this the year we will see abrupt sea ice loss?

[litesong]

... the subject of this thread doesn't attract enough comments on its own.

Seems that this thread needs some new blood. So.......
A 2012 storm broke up much Arctic sea ice & winds drove the easier to move broken sea ice to the Atlantic Ocean. Ever since, AGW deniers have doted that Arctic sea ice is on the increase.  However, solar TSI has been languid for half a century, & low for the last 11+ years(including a 3+ year period setting a 100 year record low), which should have set Arctic sea ice sky high. Yet, recent Arctic sea ice Volume has ranged between 8000 to 12,000 cubic kilometers LESS than the average of the 1980's.

[Cid_Yama]

The two papers I posted had a purpose.  One, to introduce the concept that abrupt sea ice loss can actually happen.  And two, that there are factors in both winter and summer that could lead to it.

In the winter, which we have seen happen, ocean temperatures could retard sea ice growth, even to the point where water temperature is just too warm for sea ice to form. 

And in the summer, cyclones and anti-cyclones can form, and that warm winds across the ice can cause abrupt drops in sea ice extent, as well as break up and transport the ice out of the Arctic.  The great cyclone of 2012 giving us a taste.

The concept that synoptic scale events can be responsible for the annual variance of Sept minimums.  That both weather and climate have a role. 

   

[Tor Bejnar]

I imagine a widespread rainstorm in mid-May in the high Arctic would reduce the normally high albedo (~0.9) of snow-covered ice to medium albedo (~.7) icy snow and melt ponds (ref.).  The consequences for the rest of the melting season would likely be extreme.

[Daniel B.]

I imagine a widespread rainstorm in mid-May in the high Arctic would reduce the normally high albedo (~0.9) of snow-covered ice to medium albedo (~.7) icy snow and melt ponds (ref.).  The consequences for the rest of the melting season would likely be extreme.

If that were to occur, it would enhance melt.  May temperatures are typically still below freezing, especially if clouds are blocking the sun, so any precipitation will likely fall a snow.  That is assuming that any precipitation could fall.  The Arctic is essentially a desert, with very little precipitation, so I doubt that such a large rainstorm could occur in spring.

[Dharma Rupa]

If that were to occur, it would enhance melt.  May temperatures are typically still below freezing, especially if clouds are blocking the sun, so any precipitation will likely fall a snow.  That is assuming that any precipitation could fall.  The Arctic is essentially a desert, with very little precipitation, so I doubt that such a large rainstorm could occur in spring.

The big change in the Arctic in late 2015 was the Atlantification of the Ocean and increased humidity.  The Arctic is becoming less a desert, and more a maritime climate.

[Daniel B.]

If that were to occur, it would enhance melt.  May temperatures are typically still below freezing, especially if clouds are blocking the sun, so any precipitation will likely fall a snow.  That is assuming that any precipitation could fall.  The Arctic is essentially a desert, with very little precipitation, so I doubt that such a large rainstorm could occur in spring.

The big change in the Arctic in late 2015 was the Atlantification of the Ocean and increased humidity.  The Arctic is becoming less a desert, and more a maritime climate.

That is most likely true.  However, how much change will occur is open to speculation.  The following paper does a nice job examining the potentials during the most recent ice-free era:

https://www.sciencedirect.com/science/article/pii/S0277379113004162

[Archimid]

The following paper does a nice job examining the potentials during the most recent ice-free era:

That paper doesn't say that. That paper says that it could have been ice free during the HTM under the parameters of the model. Comparing this model Arctic to present day might be slightly useful but only by understanding the difference between present day and the HTM.

The 3 biggest differences:

1. Laurentide Ice Sheet covered the Northern Hemisphere providing year round negative forcing until it melted.

2. CO2 was at 280 PPM. The extra forcing was due to solar radiation, not GHG's

3. The model in the paper works over a time period of 5,000 years, not 3 decades.

So yes, that model might offer clues, but what is happening now is different to what happened during the HTM. The paper is very clear that an ice free arctic during the HTM is not a forgone conclusion.

[El Cid]

Actually, their model is about very abrupt sea ice loss as can be seen on the attached picture. It seems relevant for 2 reasons:

1. Abrupt ice loss could happen
2. There could have been a long period (millenia) during the history of humanity without Arctic Ice, without any detrimential effects.

So my conclusions: abrupt sea ice loss could easily happen in our lifetime, but it will probably not lead to any catastrophe

[Archimid]

2. There could have been a long period (millenia) during the history of humanity without Arctic Ice, without any detrimential effects

1. The Laurentide Ice Sheet existed then and not now. It is the melting of that ice sheet what kept global temperatures from reaching Eemian temperatures in combination with highly favorable NH albedo.

  I like how this image illustrates a possible ice less Arctic with a Laurentide ice sheet.



2. At the temporal frames of this paper, which is in the thousands of years you can't say absolutely nothing about the impact it will have on modern society, which works on a yearly/decadal scale. Even if you could zoom in and examine yearly or decadal scales, human population then was in the millions and nomadic. Any climate change would have been easily adapted by migration.

Today there is no Laurentide Ice Sheet, 410PPMs of CO2 in the Atmosphere and 7 billion people most of whom live in places where the climate hasn't abruptly changed in millennia.

[Daniel B.]

2. There could have been a long period (millenia) during the history of humanity without Arctic Ice, without any detrimential effects

1. The Laurentide Ice Sheet existed then and not now. It is the melting of that ice sheet what kept global temperatures from reaching Eemian temperatures in combination with highly favorable NH albedo.

  I like how this image illustrates a possible ice less Arctic with a Laurentide ice sheet.



2. At the temporal frames of this paper, which is in the thousands of years you can't say absolutely nothing about the impact it will have on modern society, which works on a yearly/decadal scale. Even if you could zoom in and examine yearly or decadal scales, human population then was in the millions and nomadic. Any climate change would have been easily adapted by migration.

Today there is no Laurentide Ice Sheet, 410PPMs of CO2 in the Atmosphere and 7 billion people most of whom live in places where the climate hasn't abruptly changed in millennia.

Paleo data shows that most of the Laurentide ice sheet was largely gone by 8000 years ago, which the authors acknowledged was a factor up until that time.  Paleo data shows a minimum around 6000 years ago, so the Laurentide ice sheet was a non-factor at that time.  The model in their paper agreed with this data.  The Greenland ice sheet and glaciers on the Canadian archipelago would likely act similarly to the Laurentide ice sheet, limiting potential ice loss.  They listed many different feedbacks mechanisms that would likely result, but realize that sufficient knowledge is lacking as to the strength of each.  They did emphasize that hysteresis effects are much smaller than other forcings, such that an ice-free state would not be irreversible.

[Dharma Rupa]

So my conclusions: abrupt sea ice loss could easily happen in our lifetime, but it will probably not lead to any catastrophe

Would you accept replacing "probably" with "possibly"?

[Wherestheice]

Actually, their model is about very abrupt sea ice loss as can be seen on the attached picture. It seems relevant for 2 reasons:

1. Abrupt ice loss could happen
2. There could have been a long period (millenia) during the history of humanity without Arctic Ice, without any detrimential effects.

So my conclusions: abrupt sea ice loss could easily happen in our lifetime, but it will probably not lead to any catastrophe

Not lead to a catastrophe??

It will change the climate in a very harsh way. loss of albedo, latent heating, possible methane. not to mention with no ice cap, greenland will melt faster. Humans have never lived in an ice free arctic, at least since civilazation began

[Daniel B.]

Actually, their model is about very abrupt sea ice loss as can be seen on the attached picture. It seems relevant for 2 reasons:

1. Abrupt ice loss could happen
2. There could have been a long period (millenia) during the history of humanity without Arctic Ice, without any detrimential effects.

So my conclusions: abrupt sea ice loss could easily happen in our lifetime, but it will probably not lead to any catastrophe

Not lead to a catastrophe??

It will change the climate in a very harsh way. loss of albedo, latent heating, possible methane. not to mention with no ice cap, greenland will melt faster. Humans have never lived in an ice free arctic, at least since civilazation began

By civilization, do you just mean since the Greco-Roman era?

[Wherestheice]

Actually, their model is about very abrupt sea ice loss as can be seen on the attached picture. It seems relevant for 2 reasons:

1. Abrupt ice loss could happen
2. There could have been a long period (millenia) during the history of humanity without Arctic Ice, without any detrimential effects.

So my conclusions: abrupt sea ice loss could easily happen in our lifetime, but it will probably not lead to any catastrophe

Not lead to a catastrophe??

It will change the climate in a very harsh way. loss of albedo, latent heating, possible methane. not to mention with no ice cap, greenland will melt faster. Humans have never lived in an ice free arctic, at least since civilazation began

By civilization, do you just mean since the Greco-Roman era?

Before that. Research suggests modern humans have never been in an ice free arctic, let alone our civilazation https://www.nature.com/articles/ncomms6608 . An ice free arctic spells trouble for humans.

[El Cid]

So my conclusions: abrupt sea ice loss could easily happen in our lifetime, but it will probably not lead to any catastrophe

Would you accept replacing "probably" with "possibly"?

You could say possibly but I would stick to probably. Although we cannot know for sure but current models do NOT show such a sudden jump in temperatures - even with all of the Arctic Ice gone - that would cause any huge problems. I am not into modelling but the results I have seen show about 1-2-(at most 3) degree warming for NH midlatitudes for the next 20-30 yrs with the ice gone (from current levels). That is managable.
I have stated before that I see the overpopulation of Africa a much bigger problem. With twice as many people in 30-40 yrs than now, higher temps, changed rain-patterns, it would be a miracle if there would not be civil wars and mass exodus out of that continent...

[Archimid]

Paleo data shows that most of the Laurentide ice sheet was largely gone by 8000 years ago, which the authors acknowledged was a factor up until that time.

What the authors acknowledge is that they completely ignored the laurentide ice sheet

4.7 Further Aspects
Other factors of potential importance for the sea ice cover not considered in our simulations
...
Factors like the persistence of e.g. the Laurentide ice sheet until 8000 years BP (Hughes et al., 1981; Lambeck et al., 2000) probably had an impact on the Arctic climate through effects associated with both freshwater supply and surface albedo.

Paleo data shows a minimum around 6000 years ago, so the Laurentide ice sheet was a non-factor at that time.

Yes, but when the model first enters hysteresis was 11k years ago. At that time the sheet was very large. When the laurentide ice sheets are added, does the model still enters hysteresis? Unknown because the model ignores it.

[Daniel B.]

Paleo data shows that most of the Laurentide ice sheet was largely gone by 8000 years ago, which the authors acknowledged was a factor up until that time.

What the authors acknowledge is that they completely ignored the laurentide ice sheet

4.7 Further Aspects
Other factors of potential importance for the sea ice cover not considered in our simulations
...
Factors like the persistence of e.g. the Laurentide ice sheet until 8000 years BP (Hughes et al., 1981; Lambeck et al., 2000) probably had an impact on the Arctic climate through effects associated with both freshwater supply and surface albedo.

Paleo data shows a minimum around 6000 years ago, so the Laurentide ice sheet was a non-factor at that time.

Yes, but when the model first enters hysteresis was 11k years ago. At that time the sheet was very large. When the laurentide ice sheets are added, does the model still enters hysteresis? Unknown because the model ignores it.

They ignored it, because it no longer existed.  It melted millenia earlier.

[Archimid]

They ignored it, because it no longer existed.  It melted millenia earlier.

The model obtains hysterisis around 11.5ky ago.



There was significant ice in the NH at the time.



Besides the Laurentian Ice Sheet, there were remanents of the Eurassian ice sheets all the way to 8ky ago



This model completely ignores both.

[Archimid]

I would like to add that even if this model doesn't account for the ice sheets and even when proxies point to permanent cover at least at the CAB, contrary to the results obtained by this model I really like the model.

I think its result is closer to what is happening now than what was happening then, even if the warming is due to different reasons.

I imagine they didn't include the ice sheets because that would probably be years of extra research outside of their scope of interest.

[El Cid]

I think its result is closer to what is happening now than what was happening then, even if the warming is due to different reasons.

This could be true for all we know. The main point of the model is (to me) that ice loss can be very sudden, ie. happening in a few years/decades. This is most likely what we are experiencing now. Unfortunately, we do not know whether it happens in 1, 4, or 40 years from now and we also do not know what changes to atmospheric circulation it will cause...

[josh-j]

[I am not into modelling but the results I have seen show about 1-2-(at most 3) degree warming for NH midlatitudes for the next 20-30 yrs with the ice gone (from current levels). That is managable.
I have stated before that I see the overpopulation of Africa a much bigger problem. With twice as many people in 30-40 yrs than now, higher temps, changed rain-patterns, it would be a miracle if there would not be civil wars and mass exodus out of that continent...

3 degree warming at mid-latitudes is manageable? I suppose it depends what you mean by manageable but that seems a stretch.  What would such a rise correspond to as a global temperature anomaly?

Your argument around Africa seems plausible but I think that the forced migration and so on in various regions (not just Africa) could easily cause very serious problems to other countries. Plus food imports...

None of that means that everybody will die, of course. So I would be  step to know what your definition of "manageable" is as that seems key.

[crandles]

I am not into modelling but the results I have seen show about 1-2-(at most 3) degree warming for NH midlatitudes for the next 20-30 yrs with the ice gone (from current levels). That is managable.

1 Degree a decade? That is huge! Where have you seen that? (because I have heard of no such thing (Edit: perhaps I should clarify in future modelling))

I could believe 2 or 3 degrees (exc ghg effects) over 100 years or so.

[Daniel B.]

I am not into modelling but the results I have seen show about 1-2-(at most 3) degree warming for NH midlatitudes for the next 20-30 yrs with the ice gone (from current levels). That is managable.

1 Degree a decade? That is huge! Where have you seen that? (because I have heard of no such thing)

I could believe 2 or 3 degrees (exc ghg effects) over 100 years or so.

It did occur in the past, during the Bolling-Allerod warming.  However, that had extraordinary forces working then.

https://forum.arctic-sea-ice.net/index.php?topic=1952.0

[Archimid]

Over at the Ice Free Arctic  thread Ken Feldman posted this

A 2011 study estimated that the albedo effect of an ice-free arctic for a month in late summer would increase from the current forcing of 0.11 watts per meter squared (W/m-2) to 0.30 W/m-2.  Using current estimates of climate sensitivity, that would lead to a global temperature increase of 0.15 degrees C. Here's the abstract from the study:

https://forum.arctic-sea-ice.net/index.php/topic,1886.msg145111.html#msg145111


So if the ice is gone for the last month of every year, over ten years the world is more than 1C warmer. I imagine that's where the number comes from.

That said, those calculations use local and temporal forcing changes and apply them to global yearly forcing changes. That misses the whole point. That global, annual .15C become several degrees at the local level of the Arctic. That's significant because it delays the onset of the freezing season.

[crandles]

From study abstract linked by Ken Feldman and reposted by Archimid above:

Results show that the globally and annually averaged radiative forcing caused by the observed loss of sea ice in the Arctic between 1979 and 2007 is approximately 0.1 W m−2; a complete removal of Arctic sea ice results in a forcing of about 0.7 W m−2, while a more realistic ice‐free summer scenario (no ice for 1 month and decreased ice at all other times of the year) results in a forcing of about 0.3 W m−2, similar to present‐day anthropogenic forcing caused by halocarbons. The potential for changes in cloud cover as a result of the changes in sea ice makes the evaluation of the actual forcing that may be realized quite uncertain since such changes could overwhelm the forcing caused by the sea ice loss itself, if the cloudiness increases in the summertime.

28 years of change produced .1 W/m^2

radiative forcings from https://en.wikipedia.org/wiki/Greenhouse_gas

Halocarbons 0.36 W/m^2
CO2 1.88
Methane 0.49
N20 0.17
Ozone 0.4
Total 3.3

So the 0.3W/m^2 is only about a tenth of GHG forcing (maybe fifth of the warming we see taking areosols as masking half the effect of GHGs).

Warming appears less than 0.2 C per decade so a fifth of that is 0.04C per decade.

Thus 1C per decade appears like 25 times stronger than what we are experiencing. For a 3 times stronger effect (of 0.3W/m^2 vs 0.1), this does not compute. Also note the 0.1W/m^2 took 28 years to build up.

Do let me know if I am getting my sums wrong.

[Cid_Yama]

Jim White at the 2014 AGU

[Sciguy]

Over at the Ice Free Arctic  thread Ken Feldman posted this

A 2011 study estimated that the albedo effect of an ice-free arctic for a month in late summer would increase from the current forcing of 0.11 watts per meter squared (W/m-2) to 0.30 W/m-2.  Using current estimates of climate sensitivity, that would lead to a global temperature increase of 0.15 degrees C. Here's the abstract from the study:

https://forum.arctic-sea-ice.net/index.php/topic,1886.msg145111.html#msg145111


So if the ice is gone for the last month of every year, over ten years the world is more than 1C warmer. I imagine that's where the number comes from.

That said, those calculations use local and temporal forcing changes and apply them to global yearly forcing changes. That misses the whole point. That global, annual .15C become several degrees at the local level of the Arctic. That's significant because it delays the onset of the freezing season.

It's 0.15C total, not an additional 0.15C every year.  Don't forget the planck (or blackbody) feedback, which is that the temperature increase leads to more heat being shed into space.

However, over time, that 0.3 W/m-2 (about a month of nearly ice free conditions) eventually grows to 0.7 W/m-2 (the whole spring and summer ice-free) as the Arctic continues to lose ice earlier during the summer, allowing for the Arctic Ocean to warm more.  Other studies have shown that it will take decades to go from the first nearly ice free September to the whole summer being ice free.

[crandles]

Jim White at the 2014 AGU

Edited my post above.

Yes there may be records of 1C a year for 5 years or even 5 to 10C a year in the past.

Note the part I quoted

I am not into modelling but the results I have seen show about 1-2-(at most 3) degree warming for NH midlatitudes for the next 20-30 yrs with the ice gone (from current levels).

was about modelling the next 20-30 yrs

The next 20-30 years will be much like the last 20-30 years pretty much whatever we do.

[Cid_Yama]

No, it won't.

And it's beyond us being able to do anything.  Self-reinforcing feedbacks have kicked in. 

[crandles]

No, it won't.

And it's beyond us being able to do anything.  Self-reinforcing feedbacks have kicked in.

And your source hopefully specifying next 20 to 30 years?

Of course, you will be able to find a few individuals like Prof Wadhams saying such things so preferably something that has widespread support not just some nutter saying it.

(IOW I think you need a reality check.)

[El Cid]

I am not into modelling but the results I have seen show about 1-2-(at most 3) degree warming for NH midlatitudes for the next 20-30 yrs with the ice gone (from current levels). That is managable.

1 Degree a decade? That is huge! Where have you seen that? (because I have heard of no such thing (Edit: perhaps I should clarify in future modelling))

I could believe 2 or 3 degrees (exc ghg effects) over 100 years or so.

I am from Europe, and Europe (NH midlatitudes) is expected to warm this much:

https://www.eea.europa.eu/data-and-maps/indicators/global-and-european-temperature/global-and-european-temperature-assessment-5

"Annual average land temperature over Europe is projected to continue increasing by more than global land temperature during the 21st century. By the 2021-2050 period, temperature increases of between 1.0°C and 2.5°C are projected, and by 2071-2100 this increases to between 2.5°C and 4.0°C."

I also considered that most models still put ice-free arctic to happen after 2050, so they might underestimate temps IF the arctic becomes ice free soon.

So in 20-30 yrs time IF we lose all arctic ice, 1-2 degrees seem reasonable, 3 is probably a stretch.

Eastern and Northern European temperatures (see: https://data.giss.nasa.gov/gistemp/maps/) rose 1-1,5 degrees from the 80s to the 2010s (ie. 2010-17 annual averages vs 1980-1990), in a mere 30 yrs, with no sudden arctic ice loss. If we lose the ice, this could be higher, hence my numbers of 1-2 (possibly 3).