Big Freeze Plunged Europe Into Ice Age in Months - Could Melting Greenland Ice Cap Do It Again?

[steven johnson]

Looking at mud core taken from an ancient lake, Lough Monreach, in Ireland, layers were sliced from the core, just 0.5mm thick, representing a time period of one to three months. At the beginning of the Younger Dryas when it is thought that the North Atlantic circulation was turned off, temperatures plummeted over the course of just a few years, according to the mud cores.

What could initiate a similar 'Big Freeze' crisis today? The melting of the Greenland ice sheet could start of similar catastrophic collapse of the Atlantic circulation.

ScienceDaily (Nov. 30, 2009) — In the film The Day After Tomorrow, the world enters the icy grip of a new glacial period within the space of just a few weeks. Now new research shows that this scenario may not be so far from the truth after all.

William Patterson, from the University of Saskatchewan in Canada, and his colleagues have shown that switching off the North Atlantic circulation can force the Northern hemisphere into a mini 'ice age' in a matter of months. Previous work has indicated that this process would take tens of years.

Around 12,800 years ago the northern hemisphere was hit by a mini ice-age, known by scientists as the Younger Dryas, and nicknamed the 'Big Freeze', which lasted around 1300 years. Geological evidence shows that the Big Freeze was brought about by a sudden influx of freshwater, when the glacial Lake Agassiz in North America burst its banks and poured into the North Atlantic and Arctic Oceans. This vast pulse, a greater volume than all of North America's Great Lakes combined, diluted the North Atlantic conveyor belt and brought it to a halt.

Previous evidence from Greenland ice cores has indicated that this sudden change in climate occurred over the space of a decade or so. Now new data shows that the change was amazingly abrupt, taking place over the course of a few months, or a year or two at most.

Big Freeze Plunged Europe Into Ice Age in Months

[aquart]

1. So don't throw out my sweaters?

I was beginning to wonder.

[Morning Dew]

2. Wow, that's a short time frame. nm

[TreasonousBastard]

3. WEEKS! I remember when the decade time frame...

came out and that was scary enough.

A couple of weeks before an ice sheet starts moving down toward New Jersey?

Yikes!

[joshcryer]

4. I believe this was posted a few weeks back, but yeah, it's crazy, isn't it?

The idea that it can happen over a very quick time frame is disturbing to say the least. What happens to EU if the big freeze happens?

[Nederland]

8. It is crazy

The amount of fresh water flowing into the Atlantic as a result of the Greenland ice sheet melting pales in comparison to the amount of fresh water that flowed into the Atlantic when Lake Agassiz burst its banks. I've pointed this out numerous times but nobody seems to want a little thing like "facts" to interfere with their hopes and dreams of calamity occurring before our very eyes.

[joshcryer]

10. True enough, however, over time Greenland can produce the same amount of dilution.

The question is whether or not the effect happened because of a flood of dilution or because of an upper bound of freshwater. The physics suggest the latter, since seawater salinity and density is dependent upon total volume. The seas are measurably less salty.

[Nederland]

17. Disagree

I disagree with your assertion that the effect didn't happen because of the flood of dilution.

Regardless, it is irrelevant. Even at current melt rates, the number of years it will take to match the amount of water that flowed into the Atlantic when Lake Agassiz burst its banks is in the centuries. The list of other things that are going to go to shit well before then is so long it's not something we should spend any time worrying about.

[OKIsItJustMe]

5. See also

http://www.democraticunderground.com/discuss/duboard.php?az=show_mesg&forum=115&topic_id=219342&mesg_id=219342

[Bigmack]

6. THANKS for this one!

IF it was posted before, missed it then, but this is an issue I've been wondering about for several years now. Ah yes, the great irony of ironies - that human caused warming could trigger an ice age. Way to go, sapiens! Way to go..... Ms Bigmack

[Viking12]

7. Extremely unlikely.

The freshwater influx of the previous "Big Freeze" was possible because a huge store of water was released nearly instantaneously. There is no plausible way the the Greenland ice sheet could melt that rapidly independent of some other cataclysmic event.

[Nederland]

9. Agreed (nt)

[joshcryer]

11. I can't find numbers for the amount of water released during the Big Freeze, anyone have the info?

Thanks in advance if you have it. I looked at the wikipedia page but it didn't indicate.

I found this but can't access it at the moment: http://www.sciencemag.org/cgi/content/summary/312/5777/1146

[Dead_Parrot]

12. Lots

Freshwater outbursts to the oceans from glacial Lake Agassiz and their role in climate change during the last deglaciation

During this period, the three largest cooling events in the Northern Hemisphere closely followed 4 of the 5 largest outbursts from Lake Agassiz: (1) the Younger Dryas, which was preceded by a release of 9500 km³, (2) the Preboreal Oscillation, preceded by releases of 9300 km³ and 5900 km³, and (3) the “8.2 ka cold event”, preceded by a 163,000 km³ outburst; these are, respectively, fluxes of 0.30 Sv, 0.29 Sv, 0.19 Sv, and 5.2 Sv if released in 1 year. Because the influx of freshwater reaching the North Atlantic Ocean can inhibit thermohaline circulation, partly depending on whether the ocean was in a glacial, interglacial, or transitional mode of circulation, we believe that at least these large outbursts from Lake Agassiz may have provided the triggers for changes in ocean circulation and, in turn, for widespread climate change.

[joshcryer]

13. OK that's a factor of over a 100 times what is released annually from Greenland.

So theoretically in a century you could see the effects, but yeah, unless Greenland starts accelerating to 20 times what it is now we would never see it in our lifetimes.

[Viking12]

14. It's not just the total quantity, it was also the rate.

The sudden freshwater influx dramatically altered salinity in the North Atlantic messing with the currents. The same amount of water over a century would have little impact on salinity.

[Dead_Parrot]

15. Now THERE'S some famous last words...

:hide:

[Nederland]

18. To be more precise, ~836 times more

Assuming the sheet currently loses 195 km3 of water a year:

http://www.sciencedaily.com/releases/2008/09/080930081355.htm

[joshcryer]

20. The Younger Dryas is actually a factor of 48.

[Dead_Parrot]

16. There's a few unknowns, though.

We know that a sudden release of 9500 km³ killed the THC. What we don't know is where the cut off is: Would 5000 km³ have done it? 3000 km³? 500 km³? No idea.

The other unknown - and this cuts both ways - is we don't know the strength of the THC at the time compared to todays THC. Was it well established and stable? Already weakened? Again, no idea.

I'm open to anyone filling in the gaps here, BTW.

[Viking12]

19. Fair enough but frankly I think it's way at the bottom of the list of concerns.

I have a file folder of peer-reviewed articles I collected for my classes right after The Day After Tomorrow was released -- I'll see if I can dig it up. I think some of the answers to your questions are, indeed, out there.

[Dead_Parrot]

22. Thanks, it would be interesting to see some numbers... nt

[Viking12]

24. I found one of the sources online

http://www.nature.com/nature/journal/v439/n7074/full/439256a.html

The reference list provides guidance to more detailed figures. I have a few others in print versions but can't find them online.

See also:
http://www.realclimate.org/index.php/archives/2005/05/gulf-stream-slowdown/
http://www.realclimate.org/index.php/archives/2005/11/decrease-in-atlantic-circulation/
http://www.realclimate.org/index.php/archives/2006/01/atlantic-circulation-changes/

[Dead_Parrot]

25. Cheers, will do some reading... nt

[joshcryer]

21. That's a good point.

Didn't think of it that way. I am unsure now about the density vs flooding argument. I thought it had to do with overall salinity, rather than a surge of freshwater. If it is a surge, though, your point is interesting. We need a model of what it would take to do it, to get a lower bound.

500 km^3 is definitely within the realm of plausibility.

[Dead_Parrot]

23. Oh, and just to pile the doom on...

...don't forget that melting permafrost increasing flow down the Siberian & Canadian river systems. Not sure of the numbers, but +25 km³ should be in the ball-park. :)

But...

IIRC, the mechanism affected is the cooling (and evaporative salination) of the warm stream as it hits the high latitudes: fresh(ish) water sits on top of the normal salt water, acting as an insulator and preventing it from becoming more dense and sinking to the sea floor for the return leg.

The Agassiz breaches are going to be more effective at causing this, as you've got a coherent mass of water suddenly sitting on the ocean in the right place. Gradual melt from diffuse sources will be less effective as there's more time for the water to mix in: The overall salinity decreases (which drops the density and slows the current), but it's much less likely to bung a cork in the system overnight. There's a possibility that we'd get a shutdown via this route, but it's a different process which I think would take decades rather than months or weeks.

All with the caveat that I'm trying to model the fluid dynamics of the Atlantic from memory in my head, and might have missed something. :)