Arctic Ice Discussion - 2010 Freeze Up

[Gray-Wolf]

"Got some links for the 1500km inland claim?

And more verifiable the North/South Melting in Greenland over the last two years?"

==================================================================

Impacts once sea ice is removed;

http://www.colorado...._et_al_2008.pdf

http://www.agu.org/n...08/2008-22.html

http://www.scienceda...80610112628.htm (900miles is the figure here)

http://www.nature.co...te.2008.63.html

Greenland's ice loss moves North;

http://www.agu.org/j...0GL042460.shtml

http://www.nature.co...te.2010.33.html

http://www.science20...northwest_coast

I get the feeling some folk (who don't read the scientific releases) think I just make this stuff up?

As for the C.T. today data I fail to see how you cannot use the link to see the data I posted? I'll post the link again;

http://arctic.atmos....m.region.8.html

all you do is click the sea area and look at the anom.

Edited October 22, 2010 by Gray-Wolf

[BornFromTheVoid]

Data shown with no reference points does not help

What does the 0.3 mill down in Laptev actually mean in % terms?

Any area you describe as "Normal", doesn't, to me at least need "(No Ice)" as a comment, adds to the feeling that your agenda outweighs scientific analysis.

I would, for those area's that you describe as normal, perhaps give median dates for complete ice cover and compare as this year develops

Got some links for the 1500km inland claim?

And more verifiable the North/South Melting in Greenland over the last two years?

I didn't see anything wrong with GW's post. Putting in "no ice" and "normal" is just to show it isn't up to normal values because of strong ice growth, just that there isn't any expected yet. He gave the link at the bottom of his post too...

Looking at the concentration images here it seems that while there has been little outward growth in the extent, there has been improvement in concentration along the Russian coast.

Looks like the forecast for flow through Fram and backed off once again with only 2 days of northerly winds through the strait before the back eastwards into the Barents sea...

Yup Nick Sussex, it's been discussed a little before. I think it's a main part of the Arctic Amplification. Wish I could discuss it further but I've gotta run to Uni!

[Gray-Wolf]

Thanks NDS! thought I was going a bit bonkers?

Will wait for todays IJIS update but weren't you saying that these were the last couple of days for 'strong growth' before poor synoptics set in? As it is I stand by my observation that the sea ice is now extending over areas where strong heating occurred over summer and into areas that are outside the Basin.

I'm also still concerned about the 'scraped clean' channels by Melville Island as ice is still travelling into the Main NW Passage and out via Baffin (explaining some of the increases there). I'm hoping that these channels are not starting to act like 'Nares' now the land fast ice has been removed.

[4wd]

There isn't much evidence of the 1500km inland effect, it's just simulations and modelling.

The simulations also indicate that the warming acceleration during such events is especially pronounced in autumn. The decade during which a rapid sea-ice loss event occurs could see autumn temperatures warm by as much as 5 degrees C (9 degrees F) along the Arctic coasts of Russia, Alaska, and Canada.

Have we seen this happening yet?

There seems to be a tendency for rapid onset of refreeze in recent years.

[Thundery wintry showers]

Just to mention the point I made in the other thread; just because I have doubts over Gray-Wolf's insistence that we are past a "tipping point" and that he's right and that all those with open minds on the issue are wrong, it doesn't mean that I don't think the Arctic is looking "screwed" over the next couple of hundred years at least.

Unfortunately, if we aren't past a tipping point, we will probably still need global cooling of sufficient magnitude to offset the Arctic Amplification if we are to see any meaningful long-term recovery. Even stable global temperatures wouldn't be enough, because in that case we'd just be left with the Arctic Amplification creating localised warming at high latitudes offset by slight cooling across the mid-latitudes. And unless current projections of global temperature change are wildly inaccurate, it's hard to see where such a cooling comes from- the most likely scenario is a continued (and possibly accelerating) erratic rise in global temperature, combining with the Arctic Amplification and resulting in accelerating ice melt.

But it is reassuring to see that the slight recovery in 2008-2010 relative to 2007 suggests that it may not be a rapid runaway loop (not yet anyway) and so an ice-free pole might happen later rather than sooner, though it does look strongly like a "when" rather than an "if".

[NorthNorfolkWeather]

I think one of the main problems is increase in heat absorbed by the planet because of the albedo effect. I don't know if this has been covered already in this thread but its a very important component to earths temperatures.

A quick explanation here:

The classic example of albedo effect is the snow-temperature feedback. If a snow-covered area warms and the snow melts, the albedo decreases, more sunlight is absorbed, and the temperature tends to increase.

These figures show the general ability of these factors to reflect back sunlight and therefore lower the temperature.

Sample albedos

Fresh asphalt 0.04[1]

Worn asphalt 0.12[1]

Conifer forest

(Summer) 0.08,[2] 0.09 to 0.15[3]

Deciduous trees 0.15 to 0.18[3]

Bare soil 0.17[4]

Green grass 0.25[4]

Desert sand 0.40[5]

New concrete 0.55[4]

Ocean Ice 0.5–0.7[4]

Fresh snow 0.80–0.90[4]

As we can see snow reflects the most sunlight back and is crucial in terms of temp increases and decreases. As the ice melts the rate of albedo will fall and so adding to the problem.

Hi Nick,

Do you have an albedo figure for cloud? One of the "cooling" drivers is supposed to be an increase in cloud cover due to increased cloud formation due to extra ionisation from Neutrons delivered by Galactic Cosmic rays.

Edited October 22, 2010 by NorthNorfolkWeather

[Gray-Wolf]

I'm sorry if you perceive me as such TWS. I've always entertained folk's notions that run contrary to my understanding on the Arctic's prognosis but just haven't been convinced by their rational? I am where I am because , for me ,the evidence compels me to be here. I try and look for any 'positives' that the science may bring us (I'm still hoping for confirmation that we haven't got a good handle on 'isostatic rejuvenation' in Greenland and Antarctica....but none so far?) but the 'science' seems content in reinforcing my current understanding.

As far as 'tipping points' are concerned I think I'm looking at a smaller scale of such than you?

My understanding of the oceanic processes leaves me feeling that we have crossed over a certain 'tipping point' for the Arctic ocean when the loss of ice enabled 'normal oceanic precesses' to resume in the basin.

The mixing of the ocean just reinforces the inability for the ice to gain depth and so makes it liable for melt out over the next melt season (bringing open water for the mixing to resume in).

With the circulation patterns across the basin conveyering out the 'best' ice out ,via Fram, all I can now see is a 'seasonal pack in waiting' with the next occurrence of the 'perfect storm' synoptics bringing us our first 'seasonal pack' (though I'm sure it'll take a few years for things to be sufficiently changed for this to occur in an 'average' summer).

[Thundery wintry showers]

Thing is, the evidence over the last 30 years, and particularly the last 5, doesn't suggest to me that we've encountered a sudden well-defined "tipping point", but rather a gradual "shifting of the goalposts". It is clearly still possible for a recovery to occur under favourable conditions, as 2008 and 2009 showed, but the Arctic Amplification has kicked in and ensured that we need far more favourable conditions than used to be the case previously. As the ice continues to melt, the "goalposts" will almost certainly keep "shifting" in this way.

As far as I'm aware, Nick Sussex's posts are correct, albedo is probably the biggest factor in this Arctic Amplification problem.

I think we're already past the point where we can hope for a sustained recovery without an associated fall in global temperature, but I don't think the Arctic itself is at a "point of no return"- the problem is, given projected global temperature trends I don't think the kind of circumstances that are required to allow a recovery to initiate are likely to arise anytime soon, and there's a risk that if we push the climate into too warm a state, it will make a recovery highly unlikely to occur for thousands of years into the future.

[barrel1234]

so far not a very good gain of ice today, there is an area of open water surrounded by ice on the russia sid so if this starts a rapid freeze there could be a fairly large jump in updated figures later today, will have to wait and see though as we might have to wait another couple of days.

[Yorkshiresnows]

<br />Thing is, the evidence over the last 30 years, and particularly the last 5, doesn't suggest to me that we've encountered a sudden well-defined "tipping point", but rather a gradual "shifting of the goalposts".  It is clearly still possible for a recovery to occur under favourable conditions, as 2008 and 2009 showed, but the Arctic Amplification has kicked in and ensured that we need far more favourable conditions than used to be the case previously.  As the ice continues to melt, the "goalposts" will almost certainly keep "shifting" in this way.<br /><br />As far as I'm aware, Nick Sussex's posts are correct, albedo is probably the biggest factor in this Arctic Amplification problem.<br /><br />I think we're already past the point where we can hope for a sustained recovery without an associated fall in global temperature, but I don't think the Arctic itself is at a "point of no return"- the problem is, given projected global temperature trends I don't think the kind of circumstances that are required to allow a recovery to initiate are likely to arise anytime soon, and there's a risk that if we push the climate into too warm a state, it will make a recovery highly unlikely to occur for thousands of years into the future.<br />

<br /><br /><br />

I really think that we cannot state for certain what's going happen until we assess the next few years under the -PDO phase. The decline in artcic ice has more or less followed the pattern of the last 30 years (+PDO).

Global forecasts for next year look cooler, with La Nina in dominance.

Y.S

[knocker]

Hi Nick,

Do you have an albedo figure for cloud? One of the "cooling" drivers is supposed to be an increase in cloud cover due to increased cloud formation due to extra ionisation from Neutrons delivered by Galactic Cosmic rays.

If for simplistics sake we take the incoming extraterrestrial short-wave radiation to be 100 the figures break down thus. Forgetting the absorbtion fsctors, twenty units are reflected back to space from clouds, which cover about 62% of the earths surface, on average. A further 8 units reflected from the surface and 3 units are returned by atmospheric scattering. The planetary albedo is 31%.

The decrease in the albedo in the Arctic I feel has been ably demonstrated by GW and many scientific studies and I feel that a tipping point has been past. Certainly one can't be definitive about this and I wonder whether possible increased cloud cover may mitigate against significant changes in the planetary albedo. On the other hand signicant changes in circulation patterns in the arctic way well outweigh those considerations.

Edited October 22, 2010 by weather ship

[Thundery wintry showers]

<br /><br /><br />

I really think that we cannot state for certain what's going happen until we assess the next few years under the -PDO phase. The decline in artcic ice has more or less followed the pattern of the last 30 years (+PDO).

Global forecasts for next year look cooler, with La Nina in dominance.

Y.S

I was very careful in my wording- "highly unlikely", "almost certainly" etc. were my closest approaches to "stating for certain" but at no point did I make out that anything was certain to happen. However, I do see it as highly unlikely that the PDO will, in the long run, be able to overcome both the underlying global warming trend and the Arctic Amplification- we might see a few years of slight recovery but if we then get a few years of rapid melting after that, it won't be saying a lot!

One subject that my previous post hinted at, what do we mean by a "tipping point"? Is it a point beyond which the ice is guaranteed to go into self-sustaining free-fall, or more that a recovery is a lot harder and requires a more elaborate set of atmospheric "circumstances" than was true, say, a decade ago? The sequence of events from 2007 to 2009 have given me serious doubts about the former, but I'm in very little doubt that the latter is true. It could well be that confusion over terminology is generating a greater sense of disagreement than actually exists.

[nick sussex]

Hi Nick,

Do you have an albedo figure for cloud? One of the "cooling" drivers is supposed to be an increase in cloud cover due to increased cloud formation due to extra ionisation from Neutrons delivered by Galactic Cosmic rays.

Hi, yes cloud cover is generally 0.44.

I've discovered an excellent link which covers albedo in alot of detail and also has some newer info which updates those stats I put up earlier.

Very interestingly deforestation and the growth of deserts leads to an increase in albedo in these areas but this isn't offset by the loss of snow and ice on the planet. I thoroughly recommend anyone interested to have a good read of this link.

http://vsrbc.web.officelive.com/AE.aspx

Its quite interesting when you read this how a few simple measures like having white pavements and white roofs could help lower temps.

Just putting up that section:

"Cool Roofs" that alleviate effects of global warming

Massive urbanization has created sizable areas of surface of earth that are too dark and have low albedo therefore absorb heat and contribute to warming. The two key black surfaces are the asphalt roads and tar roofs. A suggested remedy therefore is White Roofs, which can help in two ways first by reducing the average temperature of cities (simple cooling) and second through reducing the amount of energy required for cooling buildings thus cut CO2 emissions (enduring cooling in future).

1. White roofs would meaningfully offset and cool the urban heat island from most cities given a predicted measurable focal cooling effect even if there is no global cooling.

2. A cooling of 5 to 7 ºF of cooling for some cities could be a worthy relief justifying the White roofs campaign.

involved. As global warming sets in and cities become larger, every city is an urban summer heat island, and these

3. White roofs campaign could avoid or minimize mortality from heat waves that are already beginning to be a deadly problem for large urban centers and would have a great cost benefit ration given that they are cheap and easy to implement.

4. Even if the long term cooling effects through reducing the CO2 emission burden on the globe is minor it is worth having.

5. The White roofs campaign would definitely operate as a significant awareness raising process for the public and political motivator for policy makers to begin to take climate chaos seriously.

Edited October 22, 2010 by nick sussex

[jethro]

My understanding of the Arctic is that it's technically a desert with very low precipitation rates. Black carbon (soot) has had a profound impact upon the ice loss, a NASA study last year claiming it to be the biggest factor in the warming and ice loss. If this is the case, how has this been factored into the albedo equations? It isn't fresh, pristine snow up there, the surface is dirty.

There's been quite a lot of talk about higher precipitation levels in the Arctic due to the warming, surely this would lead to a covering of the dirty snow and thus increase the albedo of the ice pack which is left? There may be less ice but it would be more reflective than in recent decades, especially if China keeps to the promise of cleaning up their act and greatly reducing air pollution.

[Gray-Wolf]

I think 'our' albedo changes pale into insignificance next to the loss of ice cover? Be it mountain sides loosing 'ice patches' or glacial retreats or 'melt season' exposing dark surfaces 2 weeks early or loss of arctic sea ice or loss of ice sheets (check out the reduction of 'Devonshire island' in the Canadian Archipelago!)

Clouds are (obviously ) tricky. We see more 'warming' occurring over night and this is due to the 'blanket' effect of low level clouds. So we need break the day down into 'reflective' days and 'insulating' nights. Seeing as the biggest 'gains' seem to occur over night maybe we should equally focus on how 'bad' clouds are for warming and not hope (beyond hope) that they will prove our 'saviour'?

I have to hark back to the 'unique' layering that used to exist within the Arctic Ocean. Why do folk seem to shy away from the 'irrecoverable' changes occurring there? Does it not suit their hopes for 'recovery'? The changes have occurred/keep occurring and cannot be 'repaired' by a few cold years. The layer that the 'old perennial' depended upon to reach it's fantastic dimensions has been compromised by open water and is now mixing out (making the Arctic Ocean the same as all the rest). The fact that arctic ice now only makes the same draught as Antarctic ice is surely telling? The southern ocean has no deep halocline layer (forming it each year as the temps allow ice to form) and it appears that the Arctic is now following suit (with no nurturing, 200m deep, fresh ,cold layer existing any more).

Is this not a 'Tipping Point'? if not why not? Show me how we 'recover' from it's loss.

There's been quite a lot of talk about higher precipitation levels in the Arctic due to the warming, surely this would lead to a covering of the dirty snow and thus increase the albedo of the ice pack which is left? There may be less ice but it would be more reflective than in recent decades, especially if China keeps to the promise of cleaning up their act and greatly reducing air pollution.

What good is a 'high albedo' when the first wash it gets melts it out? With swells now prowling the Arctic ocean no ice is safe from a dunking come spring. The other point being that this precipitation plunges the good ice into the melting zone leaving an impoverished pack.

Which lasts longer on your lawn 1" of ice or 1" of snow?

Edited October 22, 2010 by Gray-Wolf

[jethro]

What good is a 'high albedo' when the first wash it gets melts it out? With swells now prowling the Arctic ocean no ice is safe from a dunking come spring. The other point being that this precipitation plunges the good ice into the melting zone leaving an impoverished pack.

Which lasts longer on your lawn 1" of ice or 1" of snow?

Are you really saying that all of the Arctic ice gets swamped by swells and waves? Any plunging of ice into the melting zones would only happen on the periphery of the pack surely, the interior isn't going to weighted down by tons and tons of snow, merely cleaned up by fresh coatings of perfect powder snow.

[Gray-Wolf]

Firstly submerge yourself in this;

http://www.arctic.noaa.gov/reportcard/

Then remember the images I posted this past spring. Any area of ice less than 1km from a good drenching? Prof Barbers 'swell' had a 200m cycle and we are inundated with reports of the swell under the ice (which then breaks on the down side) across the basin.

As for weight depressing ice into the 'melt zone' how would you explain the observations we are now regaled with?

[Thundery wintry showers]

I have to hark back to the 'unique' layering that used to exist within the Arctic Ocean. Why do folk seem to shy away from the 'irrecoverable' changes occurring there? Does it not suit their hopes for 'recovery'? The changes have occurred/keep occurring and cannot be 'repaired' by a few cold years. The layer that the 'old perennial' depended upon to reach it's fantastic dimensions has been compromised by open water and is now mixing out (making the Arctic Ocean the same as all the rest). The fact that arctic ice now only makes the same draught as Antarctic ice is surely telling? The southern ocean has no deep halocline layer (forming it each year as the temps allow ice to form) and it appears that the Arctic is now following suit (with no nurturing, 200m deep, fresh ,cold layer existing any more).

Is this not a 'Tipping Point'? if not why not? Show me how we 'recover' from it's loss.

If I'm reading the above post correctly it seems to portray the "tipping point" as an absolute, black-and-white thing where once we pass it, the changes are 100% irreversible. My previous question still lies unanswered, if we're past such a point then how come there was a slight increase in ice extent in 2007-09? If it's possible for it to recover during two successive years then surely that shows that a recovery isn't completely impossible?

What I am suggesting is that the evidence we've seen so far doesn't really support the notion that we've gone past a well-defined "tipping point", but rather demonstrates the relationship where, as ice extent reduces, it becomes harder for existing ice to recover because of the resulting positive feedback loops.

However, where I don't disagree is with the overall notion that we're past a point of no return. The stronger the Arctic Amplification, the greater the amount of global cooling that would be needed to offset it, while in the meantime the available evidence overwhelmingly supports a rise in global temperature over the coming century with the main area of disagreement merely centred on the extent of the rise. If we add, say, 5C of extra warming to the Arctic, even without any kind of tipping point, the Arctic Amplification will probably end up so significant that we'll have to wait until the start of the next ice age before it can be overcome.

Edited October 22, 2010 by Thundery wintry showers

[J10]

The latest Sea Ice Extent figures are 6,268,750 km2, which is 94,420 below recent averages and 1,586,078 below longer term averages. Ice Growth this week was 85,000 which is above both short and long term averages. Ice growth seems to be better than last year, but behind how it was in 2008, it will be interesting to see if this trend continues during October.

Ranking 6th of 8 (Recent) 30th of 32 (Long Term) (Above 2007 and 2009)

The latest Sea Ice Extent figures are 7,428,594 km2, which is 271,295 below recent averages and 1,357,381 below longer term averages. Ice Growth this week was 95,000 which is above long term averages but below short term averages. Ice growth seems to be better than last year, but behind how it was in 2008, as was the trend on the previous update.

Ranking 6th of 8 (Recent) 30th of 32 (Long Term) (Above 2007 and 2009)

Arctic Ice Autumn 2010.xls

[Gray-Wolf]

Hi again TWS!

The notion of a single point in time where , once beyond, there is no return is a non-starter (I believe) but the 'sludgey zone' where we pass from what was to 'what is' i gauge to be from the early 80's to it's finally in the late noughties.

The slow reduction of the Perennial (slow basal melt through the 20th century) reached a 'break point/Tipping point when it could ship out through Fram and not cause an obstruction as it did so ( the same with Nares). Once this 'size' was reached we saw the type of shipping out that occurred in the 80's (though nobody paid much mind to this). The bulk of the ice was lost before the noughties was reached but the 'extent' did not reflect these losses (why I find it so annoying as a measure as it hid the majority of the ice we lost over the second part of the twentieth century without an eye being raised in wonder)

Once we got to the 'thin ice' we know today we had a few 'shocks' as ice 'extent' was now impacted (late /early noughties) and we could 'see' the change.

07's massive bleed of the old perennial made us all sit up.

Talk of 'recovery' since shows only ignorance of the facts on the ground (IMHO) as ice volumes continued to dip and 'old perennial' past into history. 'Extent' varies with 'weather' but the trend maintains (and grows worse) year on year.

With the majority ice so thin as to be able to melt out in a single season we were set to have the very 'protective layer', that allowed the ice to grow so deep to be mixed out by the swells that now work through the Basin (look at other studies, on other oceans, as to how this mixing works) leaving no opportunity for ice to grow to the depths it used to attain,

When there is no 'reasonable' way back to how things were is that not a tipping point?

If it takes another ice age to rebuild the layer we had is that not an example of "We Use Wishful Thinking" (W.U.W.T.) to then expect this to be just around the corner?

The newly recognised Modoki, being centred further west than the 'normal' Nino' ,sets up novel currents that impact the West Coast of America. How does this warm water input square with the cold water upwelling PDO-ve? We are just out of a Modoki so where is that warm plume headed? what does that mean for PDO-ve?

[Thundery wintry showers]

Here's a plot for Arctic sea ice volume:

http://2.bp.blogspot.com/_7pPdnIdJ3DE/S_bnV70g-bI/AAAAAAAAAdE/7X0rl7-V1co/s1600/BPIOMASIceVolumeAnomalyCurrent.png

I don't think the graph quite bears out what you're saying. Arctic sea ice volume showed no significant trend between 1979 and 1992 according to the graph, followed by a couple of sharp drops in 1993 and 1995, the latter was recovered during 1996 leaving Arctic sea ice volume at approximately the 1993 level until 2002.

Then since 2002 the trend has accelerated, with a drop between 2002-04, a stagnation in 2005/06 and then the sharp fall in 2007. Note that 2008 actually showed a slight recovery relative to 2007's ice volume, as well as extent, but then the 2009 and 2010 values dropped away again.

When there is no 'reasonable' way back to how things were is that not a tipping point?

Again, I don't think we're disagreeing on the likely outcome, but rather the reasons behind it. I think, were it not for AGW, there would be "reasonable" ways back to how things were, as illustrated by the way the ice hasn't continually fallen away since 2007, with favourable conditions enabling a slight recovery even in volume in 2008. Those "reasonable" ways would have to involve a fall in global temperature of sufficient magnitude to offset the Arctic Oscillation for the recovery to be a long-term thing, but I don't see a lot of evidence here to suggest that the required fall would have to be enough to plunge us into an ice age.

However, due to AGW we can expect the long-term trend in global temperatures to continue to be upward, and therefore, it is highly unlikely that those ways back to how things were will actually come about in the future.

If it takes another ice age to rebuild the layer we had is that not an example of "We Use Wishful Thinking" (W.U.W.T.) to then expect this to be just around the corner?

I don't recall ever saying that an ice age was just around the corner? I suggested that if we have significantly more warming in the Arctic then we may reach the stage where enough of a temperature fall to initiate a new ice age might be needed.

The observation that a warmer world will probably mean amplified warming in the Arctic and long-term melting of the ice, and that we'd need the Earth to cool to below 20th century temperature levels to enable Arctic sea ice to have any chance of returning to 20th century levels, is nothing new, and doesn't require the existence of any tipping points.

[4wd]

Tipping points are just the latest fad anyway.

Without document measurements of how such an effect occurs, it's all theory and guesswork - and as such the latest fashionable interpretation will change every few months.

[knocker]

The observation that a warmer world will probably mean amplified warming in the Arctic and long-term melting of the ice, and that we'd need the Earth to cool to below 20th century temperature levels to enable Arctic sea ice to have any chance of returning to 20th century levels, is nothing new, and doesn't require the existence of any tipping points.

That is true but isn't the tipping point the point in time when the process you describe actually accelerates due to increasing positive feedbacks? In black and white terms, when any process is irreversible.

[pottyprof]

Tipping points are just the latest fad anyway.

Without document measurements of how such an effect occurs, it's all theory and guesswork - and as such the latest fashionable interpretation will change every few months.

And your proof that it's all guess work is where?? I take it that this is just your opinion and not based on any fact?

I refer you to the first post in this thread........... Fact please and not opinion.

[Thundery wintry showers]

That is true but isn't the tipping point the point in time when the process you describe actually accelerates due to increasing positive feedbacks? In black and white terms, when any process is irreversible.

But therein lies the problem- the slight increase in both extent and volume between 2007 and 2008 suggests that it hasn't yet reached the "irreversible" stage, though it has certainly taken steps in that direction. Surely if the process accelerates due to increasing positive feedbacks, it can, under some circumstances, still be possible for those to be offset if the background "state" changes to something more favourable? I think that's what we saw during 2008, and that the problem is more that it requires prevalence of a more favourable atmospheric state than was the case before- but the feedback loops don't strike me as unstoppable just yet.

The evidence for a "tipping point" existing for the Arctic ice sheet at all is mixed, as various scientific papers illustrate. For example, there was a recent paper by Screen et al. (2010) in Nature which, while stopping short of saying we'd definitely passed a tipping point, suggested that we are seeing accelerating feedback loops at present. On the other hand, there was a paper by Notz (2009), which argued that a "tipping point" probably doesn't exist for the Arctic ice sheet at all, and that the "recent rapid retreat of Arctic summer sea ice might largely be a consequence of a slow shift in ice-thickness distribution, which will lead to strongly increased year-to-year variability of the Arctic summer sea-ice extent". However, Notz warned that substantial melting of the Greenland ice sheet is far more likely to set off a tipping point.

Unfortunately, current tipping point or no, if the globe warms by 3C or more there's a good chance that it will trigger substantial melting of the Greenland ice sheet in view of the likely amplified warming at high latitudes, and most seem agreed that this puts us at high risk of triggering an irreversible melt of the ice.