September 2007 polar sea ice anomaly

October 12, 2007 2:49 PM

Video (8MB, MPEG) of arctic sea ice extent, recorded from January to September 2007. [other formats] This summer a dramatic decrease compared to previous years in the extent of the north pole ice cap was observed. Scientists are freaked out [bugmenot]. This summer, the Northwest Passage was open for a few weeks, allowing three ships to traverse it.

This data was taken by the Advanced Microwave Scanning Radiometer instrument aboard NASA's Aqua satellite. Comparison with past years. More information here.

posted by sergeant sandwich (32 comments total)

Don't think of it as a melting polar icecap. Think of it as opening trade routes. It's an opportunity!
posted by Thorzdad at 2:58 PM on October 12, 2007

in other news Gore wins Nobel Peace prize, Fox news says the award should go to General Petraeus. instead.
posted by delmoi at 3:02 PM on October 12, 2007

Where are we going, and why are we in this handbasket?
posted by blue_beetle at 3:09 PM on October 12, 2007

Why aren't we underwater?
posted by roue at 3:53 PM on October 12, 2007

Best weather Earth's ever had; not a cloud in sight.
posted by Brocktoon at 3:54 PM on October 12, 2007

I must admit I know little, if anything, about global warming other than simple media reports. But noting that the Arctic area was only recorded since the 1970's, and the Northwest Passage is "fabled", to me meaning "heard of before", might the Arctic area shrinkage be a cyclical event? The data aren't long-term enough to show cycles, no?

I hope this is part of a cycle, but would enjoy commentary from those more environmentally educated.
posted by frumious bandersnatch at 4:18 PM on October 12, 2007

frumious bandersnatch writes "I hope this is part of a cycle, but would enjoy commentary from those more environmentally educated."

I think that with the typical pattern, we should be entering a new ice age pretty soon. However, given that we've spent the past couple centuries furiously pumping all the greenhouses we can find into the atmosphere, the next ice age might be a bit late.
posted by mullingitover at 4:23 PM on October 12, 2007

V e r y interesting.
posted by Emperor SnooKloze at 4:26 PM on October 12, 2007

It seems a bit disingenuous to show a video of the icecap from the beginning of summer until the beginning of winter. Of course it'll be shrinking dramatically over that period.

Frumius: The Northwest Passage is "fabled" because early explorers kept looking for it (and dying in the ice). AIUI, it's not something that was historically traversible without an icebreaker. The recent opening of the passage is definitely a new thing on human historical timescales.
posted by hattifattener at 4:26 PM on October 12, 2007

I read through the slashdot thread when the passage opened up. Someone posted a stat that antarctic ice had actually hit a record high this year. A lot of people debated what it meant. Some seemed to think this was proof that we didn't need to worry about arctic ice, even though arctic ice was down about 20% and antarctic was up by about 2%.

On the same site I found this long-term chart of global sea ice, which seems to show that year to year fluctuations are common but there is a clear slow decline over the last 20 years.

p.s. The Northwest Passage is 'fabled' because explorers have been searching for it for 400 years; it was never navigable until now unless you had an ice-fortified ship. Originally the British had assumed it existed (without proof) due a false belief that seawater cannot freeze.^
posted by PercussivePaul at 4:30 PM on October 12, 2007

When the scientists are surprised by a 1 year change, that makes me wonder about their 100 year forecasting abilities.
posted by smackfu at 5:02 PM on October 12, 2007

Smackfu, the IPCC projections have been conservative. The intent of the IPCC is to give credence to the effects of anthropogenic climate change. For far too long we believed that environmental groups and their members have gone beyond the realms of logic to instill a morbid fear of what terrible things awaited us. The things that would happen if we committed ourselves to unparalleled levels of consumption and waste. We were told of a world without potable water, of toxic skies, and of forests devoid of life.

The IPCC does not wish to be disregarded as doom sayers.






However, it is most unfortunate that doom is exactly what is in store for us.
posted by PROD_TPSL at 5:25 PM on October 12, 2007 [1 favorite]

"The world isn't going anywhere: WE ARE!"
- George Carlin
posted by ZachsMind at 5:52 PM on October 12, 2007 [1 favorite]

I just started letting myself get scared about that damn hole in the ozone and now this.

Goddamnit.
posted by milarepa at 8:27 PM on October 12, 2007

Why aren't we underwater?

Mostly because liquid water occupies the same volume that ice displaces, so melting ice that has been floating won't change the volume of the ocean.
posted by b1tr0t at 9:35 PM on October 12, 2007 [1 favorite]

No, b1tr0t.

The ice that will raise sea level is the ice that is on land (Greenland and Antarctica most notably) and is usually referred to as ice sheets. The floating ice such as in icebergs or ice shelves when melting does not raise the sea level because water will fill up the space the ice displaces.

In any case, sea level will rise dramatically in extreme events known as ice sheet collapse. These phenomena have a very distinct but low probability of happening in the near future. Some models though show that the probability increases alarmingly 50years from now in a business-as-usual scenario.
posted by carmina at 10:36 PM on October 12, 2007

The problem with polar and particularly the Arctic ocean sea-ice is this: the Arctic is the area of the world that shows the fastest increases in temperature right now. Snow/ice cover reflect sunlight back into the atmosphere, the albedo effect. Open (ice free) ocean water is darker and absorbs sunlight more, thereby increasing the temperatures, and finally not allowing new ice to built up. This is the so called positive ice-albedo feedback. And that is why the low sea-ice concentrations are so worrisome: the system cannot bounce back that easily. Estimates claim that Arctic will be ice-free within 50 years and may well remain ice free for decades, with huge geopolitical (oil, navigation, displaced fisheries) and economic consequences. Not just enormous flooding and destabilization of the permafrost.
Furthermore, the North Atlantic and its part adjacent to the Arctic is in fact the most important sink of atmospheric CO2 which is absorbed and transported into the deep ocean with the thermohaline circulation and residence times of thousands of years. Sea water absorbs CO2 better the colder it is. Warming Arctic, warms the Atlantic, reduces the uptake of CO2 from the atmosphere, further burdening the system. Another positive feedback.
Just two of the main reasons we want a cold, icy Arctic. Ask the Inuit.
posted by carmina at 11:38 PM on October 12, 2007

my understanding of warming-induced sea-level rise is that the major contributor is not melting ice, but in fact thermal expansion of the water.

to estimate:

the thermal expansion coefficient of water is ~ 2.5 x 10^-4 K^-1.

the volume of water is ~ 1.3 x 10⁹ km³, and the area of the earth covered by water is ~ 3.8 x 10⁸ km²

so, per degree, the volume of the ocean should expand by 1.3e9 * 2.5e-4 = 325,000 km³. spread over the entire surface area of the ocean, this is a rise of 325000 km³ / 3.8e8 km² = 8.5 x 10^-4 km. that is 0.85 meters per degree C, or about two and a half feet.

as for whether we are underwater or not, ask the residents of new orleans what they think.
posted by sergeant sandwich at 1:41 AM on October 13, 2007 [5 favorites]

Arctic sea ice loss compared to IPCC models
posted by sfenders at 4:27 AM on October 13, 2007 [1 favorite]

When the scientists are surprised by a 1 year change, that makes me wonder about their 100 year forecasting abilities.

This is a common fallacy. No one can forecast the stock market price tomorrow. But just about everyone can forecast the stock market will be up in 10 years. That's the difference between weather forecasting and climate forecasting. The specifics will usually be a surprise, the general trends will not. In fact, the longer the forecast, the easier it gets because averages play a larger role and smooth out the peaks and valleys of the specifics.
posted by stbalbach at 5:40 AM on October 13, 2007 [1 favorite]

But noting that the Arctic area was only recorded since the 1970's

We know this is an unprecedented event based on multiple sources of evidence not just satellite: Arctic ice algae and other micro-organisms, walrus and polar bear populations and human inhabitants, such as the Inuit.
posted by stbalbach at 5:50 AM on October 13, 2007

sergeant, I agree, right now thermal expansion is the largest term in the sea level change equation but it amounts to half a meter *at worst* in future climate projections. However, none of the models that went into IPCC-AR4 included ice-sheets (we did not know how to model them, back then!) and therefore did not include the leading order term which is the collapse of the ice sheets and the massive fresh water flux (streams or pulses) into the ocean. It is estimated that moderate collapse could lead to sea level rise of about 6feet globally. How probable and how rapid these extreme events are, is a whole other discussion, but there is evidence from previous geological deglaciations:

..the most well-documented of these pulses occurred about 14,200 years ago and is known as meltwater pulse 1a (MWP 1a). Evidence for MWP 1a has been found in corals from Barbados, Tahiti, and Southeast Asia (8,9 and 10). These coral records show that sea level rose by 16 m over 300 years, an average rate of about 50 mm/year - twenty times faster than the current rate of sea level rise.

For this reason alone, the recent IPCC is considered by many, a conservative understatement of the sea level rise. Another effect that is commonly overlooked is the continental (or isostatic) rebound: as ice cover over land reduces, land masses rise, changing the geoid of the earth, bringing previously "safe" regions near or under water level and vice versa. This effect is also not included in IPCC models.

But the real issue is not whether sea level will rise by 1 or 2 meters or 10. It is really that tides and storm and hurricane surges will be added to that rendering many areas endangered by large scale, occassional flooding.
posted by carmina at 7:56 AM on October 13, 2007 [1 favorite]

6feet, my ass!

ahahaha! I meant 6 meters!
posted by carmina at 8:27 AM on October 13, 2007

so, per degree, the volume of the ocean should expand by 1.3e9 * 2.5e-4 = 325,000 km3.

There's an implicit assumption in this otherwise apparently correct calculation that all parts of the ocean will change temperature at the same rate -- when in fact the top of the ocean will warm much more quickly than its deeper reaches (which account for the majority of the ocean's volume).

It's hard to modify the calculation to take this fact into account though. You'd really have to have some sort of model as to how warming propagates down to the bottom layers of the ocean -- it's probably mostly done by conduction as convection would actually work against you so it would be quite slow.
posted by lupus_yonderboy at 9:10 AM on October 13, 2007

To be a little more specific, that would mean that if you thought of "ocean temperature" as the "ocean's near-surface temperature" (aka "what we can easily measure") then the result of 0.85 meters per degree C from sergeant sandwich's calculation would have to be reduced by some compensating factor (very roughly, between 1 and 10) for the slowness of transmission of thermal energy to the lower parts of the ocean.

As I read it, we do get a useful long-term damping effect from the deep ocean, which cools (through convection and conduction) more easily than it heats (though conduction alone).

But of course this is a fairy story without data and a model: for all I know, the ocean mixes very quickly from top to bottom and the compensating factor above would be 1, meaning no effect at all and this whole argument meaningless! :-D (though I'd be surprised... I'll bet it takes a hundred years for a water molecule to progress from top to bottom of the ocean...)
posted by lupus_yonderboy at 9:26 AM on October 13, 2007

The specifics will usually be a surprise, the general trends will not.

Doesn't that mean that stories like the original post are meaningless? Essentially the same as someone saying a cold winter means global warming is false. Why would scientists be "freaking out"?
posted by smackfu at 9:34 AM on October 13, 2007

yonderboy, diffusion is the process that transfers heat from the upper layers of the ocean to larger depths. Molecular diffusion is indeed very slow (0.001 cm^2/sec). It would take about 12 years to diffuse heat from the surface to 4000m depth, the average ocean depth. BUT, it is turbulent mixing which can do the job 3 times as fast (1cm^2/sec) and that is quite fast compared to the fact that surface temperatures have been rising over the last 50-100 years. These are very crude estimates I am giving you here as I am leaving out deep convection, internal wave breaking, entrainment and the suchlike which may increase the rates.
posted by carmina at 9:40 AM on October 13, 2007

ugh, 3 times as fast should be 1000 times as fast. Idiot. Me. I need coffee. Beans.

smackfu, scientists are concerned, alarmed because of the positive feedbacks, I mentioned earlier. I do not think scientists freak out. They are too cool. :)
posted by carmina at 9:44 AM on October 13, 2007

Okay, I am all wrong, obviously. It is 1200-5000 years that it would take molecular diffusion to heat up the ocean. If you want to test this take the diffusion equation dT/dt =Kd^2T/dz^2 and do the math. The 12 years is really for the turbulent mixing rates that's applicable in the real world.

sorry yonderboy. I go away now.
posted by carmina at 10:09 AM on October 13, 2007

The ice that will raise sea level is the ice that is on land

Right, that's the converse of what I said.
posted by b1tr0t at 11:18 AM on October 13, 2007

Not entirely. See, in the question "why aren't we underwater?" your answer is insufficient because it does not bring up land-ice. Your answer maybe mistaken as "we will never be underwater, because sea-ice melting will never change the levels". Do you see what I mean? Please tell me you do, because my head hurts.

mind you, this exactly is one of the most persistent arguments global warming sceptics make.
posted by carmina at 12:27 PM on October 13, 2007

1. This post is about arctic sea ice, which floats.
2. Someone asked why we aren't under water.
3. I answered that we aren't under water because floating ice displaces the same amount of water whether is it liquid or solid

Land ice matters in the big-picture discussion of sea level rise, but so does evaporation rates due to higher temperatures, crust rebounds rates, etc. Displacement is a sufficient answer when the discussion is about the melting of arctic ice.
posted by b1tr0t at 2:29 PM on October 13, 2007