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Geology - North Atlantic Current shutdown

Expert: Keith Patton - 11/4/2009

Question
QUESTION: How much ice would need to melt and flow into North Atlantic to shut down the North Atlantic Current? What effect would the shutdown of the North Atlantic Current have on the world climate (and on Europe in particular)? How much would this raise sea level? Could the impact of an asteroid (a small one, not a big world-destroying one) in Greenland be a reasonable cause for the melt, as opposed to global warming?

I know the effect would be nothing like in the movies. I'm writing a story where European civilization collapses before Columbus sails to the Americas, and I need a scientifically plausible cause for the demise of European society but not other societies. Thanks!

ANSWER: I don't know how much ice would have to melt, the mathmatics are beyond me. The current could be disrupted by the influx of fresh water diluting the hypersaline water flowing south which would upset the Gulf Stream fed North Atlantic current which keeps N. Europe warm.

One look at a map of the world with an eye to the northern latititudes should tell you what would happen to N. Europe should the current be disrupted. Great Britain is on the same latitude as Hudson Bay. France is on the same latitude as the Dakota's and Montana. Norway and Findland...forget about it. Large areas of the most productive agricultural land in W. Europe would see massive temperature drops, and areas that usually have ice free ports year round would start to freeze up. Almost all of most populous areas of W. Europe are on the same latitude as Montana and S. Canada. There is a reason most of the Canadian population lives within 300 miles of the U.S. border. N. Canada turns into a deep freeze in winter. I have seen -30F below zero in the Montana flatlands in November.

I answered this same question for a screen writer about 7-8 years ago. The movie the Day After Tomorrow came out the next year. He sped the time line up from about 10,000 years to several weeks for dramatic impact. The big storms were a fiction too.

Assuming that all the ice caps melted, 80 meters (240 feet) is the accepted estimate in the rise of sea level. Greenland alone would account for only a modest 6.5m (20 foot) rise in seal level.
Antarctic is the monster with almost 30 million km3 of the worlds' glacial ice. It would result in a 73m (219 feet) rise.

A meteor impact would melt ice and break up the ice sheet speeding up the melting process, but that would be short term. In fact, the disruption of the current would lead to a plunge into a cooling cycle.

http://pubs.usgs.gov/fs/fs2-00/

Your on the right track. I should think that the a meteor impact which could cause a rapid melting if only temporary surge of fresh water could cause a major albeit temporary disruption of the current, leading to a series of horrible winters, leading to ice bound ports, destruction of fishing fleetes (the Basques were fishing the New Foundland cod banks during this time feeding the insatiable hunger of Christian Europe for fish for their religious observances. (See Mark Kurlansky's Cod: The fish that changed the world for more background info)

This breakdown of systematic order could lead to a wave of chaos like that seen during the 100 years war and during the black death. Remember too that people would be forced inside for warmth as would their nemisis the rat, leading most likely to outbreaks of the Black Death and Scrub Typhus as refugees crowded into the cities as crops failed and live stock died. Religious zealotry would also take hold as opportunistic "prophets" spread the word of the second coming and end of days stuff like occurred during the times of plague. There might also be another incursion of nomadic invaders from Central Asia as they also migrated in search of warmer and more fertile grass lands on which to graze their horse herds.

There would be a domino effect of sorts that could last for a number of years.
Here is the article I referenced to the other writer published in the Atlantic Monthly on the disruption of the Atalantic current:

http://williamcalvin.com/1990s/1998AtlanticClimate.htm

---------- FOLLOW-UP ----------

QUESTION: Hi, I thought of a few followup questions I hope you can help me with. Where in Greenland would be the best location for a meteor impact so as to allow meltwater to drain off and interfere with the North Atlantic Current? I was thinking somewhere along the eastern coast, but I don't know exactly where. The Scoresby Sund is the biggest fjord in the world, so hitting an ice dam there might be good, if perhaps a little too coincidental. I know you don't have the specific numbers, and the damage would depend on the size of the meteor (which can change as needed), so I'm just looking for an educated guess.

Rather than a continual melting as is occurring now with global warming, the impact would produce a relatively brief flood of meltwater. If this were to interfere with the thermohaline circulation, would it result in an unstoppable chain reaction type effect, shutting down the North Atlantic Current? Is it possible for the current to be disrupted or slowed temporarily (say for a few years) before restoring itself? The Calvin article states that "local failures can occur without catastrophe," but I don't know what would be the relative scale of a failure caused by impact meltwater. I assume if the NAC shuts down entirely, we might have a situation similar to the Younger Dryas, and I don't want that to happen.

If the NAC is disrupted briefly (maybe a few years to a decade), I know this will have a significant impact on northern and western Europe, but what about further inland? Would eastern Europe (including European Russia) and southern Europe also have similarly bad winters? I'm also concerned about the potential effects of this situation outside of Europe. Would other areas of the world be significantly affected if the NAC disruption is only brief? Basically, I'm trying to reach a happy medium in which Europe is crippled by abnormally cold weather but in which other areas of the world are relatively unaffected.

Thank you so much for your help!

Answer
North East or Central. The drainage of Greenland appears to to to the east, but a large impact would really stir things up. Looking at the diagrams in the article, it looks like a large influx of fresh water from the large fiord would disrupt the hypersaline south bound loop between Greenland and Iceland. So that would work I think. The placement isn't that important as an impact would melt ice and the runnoff would go to the south and east. An impact in the central part of the continent would be in the area of the thickest ice so you'd expect a larger volume of melt water cascading to the east.

See here for a nice thickness map:

http://en.wikipedia.org/wiki/Greenland_ice_sheet

The thickest ice is just west of the large fiord and almost central to the continent.

I think greater Europe would be affected that is the Ukraine and parts of eastern Russia, but that would not be on the scale of Europe with such a dense population. I should think N. America and the tropics would not be affected much if at all except the cascade effect on the global economy...what would we do without french cheese and wine and german bier!!??

Certainly the effects would last a generation or more before anything like the Younger Dryas kicked in. We are talking hundreds to thousands of years here. The impact would probably be pretty rapid as the ports froze up and the weather- the mean annual temperatures plunged in the Western European countries. Ireland and England started seeing perenial ice fields forming in the highlands as does Spain and S. France. Glaciers started to advance in the Alps, Norway and Scandinavia. Project what you see in N. Canada to the same latitudes in Europe. the impact on Great Britain, Norway, Sweden, Denmark, Netherlands (no more tulips!) and Belgians (a return to the dark ages for the monks which might help their production of belgian ales if they can get grain!) The North Sea and Baltic would become ice bound not fully breaking up after winter.
The ice hazard and conditions would impact oil and gas production in the N. Sea and raise the cost of production, like in the Barent Straits, curtailing the funds from oil production when Great Britain, Norway and others need it the most. Civil unrest in Great Britain would escalate as a lower and middle class used to being taken care of by the socialist system rebels due to soaring heating and food costs. The ice would do what the Nazi submarines failed to do in WWII, cut off the islands from the rest of the world.

I think you's see the European Union break up as those less impacted would not want to bear the burden of those hardest hit. Old nationalism would raise its head. Weakened authority might see opportunistic factions..radical Muslims in France and Spain...take advantage.

The rest of the world might see lower oil prices if the demand in Europe was curtailed by crisis.
You cold see factions in W.Russia, Poland sabotage pipelines for delivery to oil and gas to W. Europe as panic gripped those areas and fear that they shouldn't be sending "their" oil and gas away when they might indeed need it themselves.

I generally thing you can find your happy medium, since no one really knows the rapidity such events would take. I am sure you can find ways that Europe becomes isolated. The US might have to start actually producing a lot of stuff at home rather than importing it. Or we shift the trade to Asia or revert to isolationism as politics at home force our government to pull back from Europe as things cascade out of control.

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