We covered this topic before on WUWT, but it showed up again in this week’s AGU highlights. Given the attention to the recent Arctic sea ice low and quick turnaround, I thought it would be appropriate to mention again.
From the American Geophysical Union highlights
The Arctic has been losing sea ice as Earth’s climate warms, and some studies have suggested that the Arctic could reach a tipping point, beyond which ice would not recover even if global temperatures cool down again. However, a new study by Armour et al. using a state-of-the-art atmosphere-ocean global climate model finds no evidence of such irreversibility. In their simulations, the researchers increase atmospheric carbon dioxide levels until Arctic sea ice disappears year-round and then watch what happens as global temperatures are brought back down. They find that sea ice steadily recovers as global temperatures drop. An implication of this result is that future sea ice loss will occur only as long as global temperatures continue to rise.
Source: Geophysical Research Letters, doi:10.1029/2011GL048739, 2011 http://dx.doi.org/10.1029/2011GL048739
Title: The reversibility of sea ice loss in a state-of-the-art climate model
Authors: K. C. Armour: Department of Physics, University of Washington, Seattle, Washington, USA;
I. Eisenman: Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, USA, and Department of Atmospheric Sciences, University of Washington, Seattle, Washington, USA;
E. Blanchard-Wrigglesworth, K. E. McCusker, and C. M. Bitz: Department of Atmospheric Sciences, University of Washington, Seattle, Washington, USA.
Key Points
- Sea ice loss is reversible within a state-of-the-art global climate model
- We find no evidence of threshold behavior in summer or winter sea ice cover
- Rapid sea ice retreat does not imply irreversibility
Abstract:
Rapid Arctic sea ice retreat has fueled speculation about the possibility of threshold (or ‘tipping point’) behavior and irreversible loss of the sea ice cover. We test sea ice reversibility within a state-of-the-art atmosphere–ocean global climate model by increasing atmospheric carbon dioxide until the Arctic Ocean becomes ice-free throughout the year and subsequently decreasing it until the initial ice cover returns. Evidence for irreversibility in the form of hysteresis outside the envelope of natural variability is explored for the loss of summer and winter ice in both hemispheres. We find no evidence of irreversibility or multiple ice-cover states over the full range of simulated sea ice conditions between the modern climate and that with an annually ice-free Arctic Ocean. Summer sea ice area recovers as hemispheric temperature cools along a trajectory that is indistinguishable from the trajectory of summer sea ice loss, while the recovery of winter ice area appears to be slowed due to the long response times of the ocean near the modern winter ice edge. The results are discussed in the context of previous studies that assess the plausibility of sea ice tipping points by other methods. The findings serve as evidence against the existence of threshold behavior in the summer or winter ice cover in either hemisphere.
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I’ve lost the link, but I read once of three polar expeditions, in the years 1822 – 1870, collectively seemed to document the partial loss and reformation of the Arctic icecap. Does this ring any bells with anyone? I’d like to know more about what they observed.
I am SOOOOO glad they discovered this. Once, when I was at band camp, I took the ice cube tray out of the freezer and the ice all melted, so I threw the ice cube tray away.
Dave Springer says:
Wow, Dave. You really knocked the heck out of your strawman there! Of course, scientists have never said it can never come back. The question has always been to what degree there is hysteresis, so if, for example, temperatures heated up and then returned to present values, would the arctic ice recover to current levels (and how quickly)…Or does it require cooling to lower values to re-establish the ice at current levels?
Once it gets hot enough to destroy man and in the series after man, the temp. will drop back and the ice will refreeze. Yes, Hansen will get his return of the ice age of 1977. Too little CO2 will destroy the planet, wait a second, heat is going to. Hum, maybe everything will evolve some more? Darn, I am confussed…….. 🙁
Let’s hope that the Earth doesn’t revert to its Neoproterozoic state of Snowball or Slushball Earth (does ice have a memory?). In fact, a readible and sensibly-written Wikipedia article (sorry, but I was rushed, and actually the article is quite good):
http://en.wikipedia.org/wiki/Snowball_Earth
describes a relatively new line of thought that suggests we might have far more to fear from cooling than we do from AGW, to wit: “…The idea is that Earth’s carbon-based life forms affect the global carbon cycle and so major evolutionary events alter the carbon cycle, redistributing carbon within various reservoirs within the biosphere system and in the process temporarily lowering the atmospheric (greenhouse) carbon reservoir until the revised biosphere system settled into a new state. The Snowball I episode (of the Huronian glaciation 2.4 to 2.1 billion years) and Snowball II (of the Precambrian’s Cryogenian between 580 – 850 MYA and which itself had a number of distinct episodes) are respectively thought to be caused by the evolution of aerobic photosynthesis and then the rise of more advanced multicellular life and life’s colonization of the land.[74][75]…”
We’re down so low in CO2 content of the atmosphere that colder climate is probably much more likely than warmer (can anyone definitively state that the Quaternary Ice Age is over?). Perhaps Trenberth’s great (unseen, unmeasured but model-proven) deep-sea warmth accumulation will rise up to save us. LOL
Based on a model? Why should I give this any greater weight than all the doom and gloom models?
The dates for the progressive disappearance of ice are from March until until September.
Is Obama going to outlaw summer?
And why 2007?
@joel Shore
Good to see you posting again.
Strawman? I believe Dave Springer was accurately commenting on this point in the article: “The Arctic has been losing sea ice as Earth’s climate warms, and some studies have suggested that the Arctic could reach a tipping point, beyond which ice would not recover even if global temperatures cool down again.” (bold mine)
I had similar thoughts as Mr. Springer.
charles nelson says:
September 21, 2011 at 6:34 am
You’ve got a good point, Charles. Wouldn’t it have been easier just to take a bucket of seawater, put it in a deep freeze for three months with the door shut and see if it turns to ice? They would have saved a whole bunch of CPU cycles.
To think that humans have anything to do with global climate is absurd. The only differences are in a parking lot in open sun in July. We need to bring back Mr. Bill “Oh Noooooooooooooooo”
Joel Shore says:
September 21, 2011 at 6:31 pm
You’d start to get sea ice the moment the surface temperatures in the Arctic caused the seawater at the suface to go below the freezing point of seawater. It would grow proportionally to the amount of heat removed. History at that point is totally moot–fantatsical–mythical.
Sea ice does not have a memory, and by the same token, seawater doesn’t have a memory either. This “tipping point” you refer to doesn’t apply–seawater isn’t some mechanical contraption; we’re talking about freezing water here.
You do realize that this is an argument for reducing emissions, right?
Not really. There is no reason based on this for emission reduction or anything else. Leaving aside the obvious facts that warmer is better for the environment as is increased carbon dioxide, this entire paper is based on the reactions of a model. The reactions of the model are not indicative of the real world in any way, In other words this is a waste of paper.
H. R. says:
Well, perhaps they were not as clear as they could have been…but the point is that they were talking about there being a hysteresis effect, so as it says, when you lower the temperature back down to a certain point, the ice doesn’t necessarily assume the same extent it did when you were at that temperature on the way up. You might want to look at a hysteresis curve for magnets to understanding the concept here: http://en.wikipedia.org/wiki/Hysteresis
@joel Shore says:
September 22, 2011 at 10:47 am
Agreed… they weren’t clear at all in that quote and it did tend to make one’s head snap back that they’d say such a thing. (Who knows why they’d say something that daft.) So… many here had a little (a lot!) of fun with that.
Yup, I understand the hysteresis thingy having to work with it and around it on a daily basis. Of course the ice would return when it’s cold enough but I would think that it would be slower to re-establish the arctic ice if it ever were to actually become ice free. The various currents would have their way with the baby ice until the ice could get firmly established. And if humans and ice breakers are still around at such a time, I’m sure they’d work like the dickens to keep the ice from re-forming. There’s a lot of value in an ice-free Arctic Ocean!
RockyRoad says:
It is probably a cleaner experiment to talk about lowering the greenhouse forcings back to the original level than the temperature back down to the original level. In that case, some hysteresis is indeed possible because an earth with more ice coverage will tend to reflect more of the incident solar radiation than an earth with more ice coverage. So, yes, there is the possibility of more than one metastable state existing for a certain level of greenhouse gases. (A dramatic example of this that may have occurred in the past is the transitions back-and-forth between iceball or slushball climates and warmer climates.)
With temperature, the arguments are a bit subtler…but I think it is still possible to have the same global temperature but have the distribution be different. Or, as H.R. notes, the various currents could be different.
But, again, like I said, it is probably easier to visualize hysteresis occurring in the context of bringing the greenhouse gas forcings back down to the original level rather than the temperature back down to the original level.
Vaguely related. The North Pole cam image suddenly showed a current image today but there is not much to see. It appears, as I suspected, the cam is now buried in snow / ice.
@joel Shore
“[…]
But, again, like I said, it is probably easier to visualize hysteresis occurring in the context of bringing the greenhouse gas forcings back down to the original level rather than the temperature back down to the original level.”
I tend to visualize the ice core data where CO2 levels lag temperature changes by 800ish years. The input stops and the response continues for a bit.
OK, the cam is not buried yet. It was iced over. The ice is now sublimating away. Nice sunset underway but can’t see too much.