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Will the melting of the Polar Ice Caps affect the Gulf Stream?

We are all obviously very concerned about global warming in this country and I understand that one of the effects may be the melting of the Polar Ice Caps. Will this melting affect the Gulf Stream which gives the UK a warmer climate than countries on similar latitudes and will the resultant cooler climate mitigate any affect from the increase in temperature from the sun by the increase in greenhouse gases?
Christopher Jones from Greater London (Age 45-54)

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3 Responses

  1. There is considerable uncertainty surrounding this issue. The input of melted ice from the Arctic is very unlikely to have much impact on the Gulf Stream, but it could affect the North Atlantic Drift (which is the current that brings warm waters from the Gulf Stream ovver towards the UK). Whether it will affect the NAD enough to cause a localised cooling over north-west Europe is unclear.

    At the moment, I think the current research suggests that even if this does happen, it will only be enough to partially offset the warming that results from the higher mean global temperature, and probably only temporarily. It would be foolish to rely upon this scenario for helping the UK to cope with whatever climate change we face in the next couple of centuries, as at best it would probably only be temporary, and most likely followed by a sudden warming once the ice flows abated.

    Ian Simpson, PhD student, Climatic Research Unit of the University of East Anglia

  2. The short and simple answer is yes, however it’s not really quite that simple or short!
    There is a lot more to the Gulf stream than many people realise, it is influenced greatly by the thermohaline circulation – which is a world wide movement of water that depends on heat and salinity.
    Thermohaline circulation could be disrupted if the ocean surface gets a layer of fresh water.
    This might result from changes in Arctic winds that move sea ice from Arctic Ocean through Fram Strait into the North Atlantic.
    Sea ice in Arctic Ocean is fresh. When ice moves south through Fram Strait it melts to create a layer of fresh water. This is less dense than saltwater and so tends to stay on top of the ocean.
    This discourages the normal process of sinking at high latitudes that supports thermohaline circulation – makes it harder to move the warm water north from the equator.
    This stagnation process happened over a period of years in late 1960’s and early 1970’s (the great salinity anomaly).
    Additionally during winter the Arctics atmosphere is very cold, in comparison the ocean is much warmer
    Sea ice cover separates atmosphere and ocean preventing heat exchange. Another way in which sea ice helps to keep the Arctic cold.
    But heat escapes well from areas of thin ice and especially from small openings in the ice cover (leads and polynyas).
    Approx half the heat exchange between Arctic Ocean and atmosphere occurs through openings in the ice
    With thinner ice and more leads and poynyas the sea ice cannot efficiently insulate the ocean from the atmosphere.
    The Arctic then warms which influences circulation of atmosphere.

  3. Water at the surface of the ocean in the North Atlantic is cold and relatively salty, and this makes it dense, so that it sinks to the bottom of the ocean, forming what is known as North Atlantic Deep Water. This sinking leaves a gap behind it, and that gap helps to draw the Gulf Stream north so that it flows past the UK and gives us our relatively warm climate.

    If the Greenland ice cap starts to melt due to rising temparatures, a lot of fresh (not salty) water will pour into the North Atlantic. This will make the surface water in the North Atlantic less dense, and it will be less inclined to sink. Less sinking means the Gulf Stream will not be drawn north as strongly.

    There is evidence that the formation of North Atlantic Deep Water has weakened in the past as climate changed, and the effect is also shown in computer models of both past and future climate. However, the climate system is so complex that it is currently hard to say what will happen for definite, but the weakening or complete shutdown of North Atlantic Deep Water formation is certainly a possibility.

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