Climate Feedback

Gulf Stream revisited

cover_nature.jpgIt’s been quite a while since the Gulf Stream was last on the Nature cover. This week the old highlight is back.

Now that’s a topic which has caused an awful lot of confusion before. “How global warming will cause the next ice age”, stuff like that. So just to be clear: the Gulf Stream is the mostly wind-driven upper limb of the Atlantic meridional overturning circulation, which ceaselessly transports warm surface water from the Caribbean to middle and high latitudes on the other side of the Atlantic. Yes, ceaselessly. As long as the Earth keeps rotating there’s really nothing in the world (not even global warming) that could bring it to a halt.

It is common knowledge – and true – that the British Isles and Scandinavia enjoy a much warmer climate than Newfoundland or Labrador thanks to the Gulf Stream. But its climatic influence goes far beyond that, a US-Japanese team report in a paper in Nature this week.

They detected the Gulf Stream’s signature in the entire lower atmosphere – namely in air and cloud temperatures, rain bands, pressure fields and wind convergence – above its meandering cross-Atlantic course, and far inland in Europe.

That the influence of the Gulf Stream might penetrate deeply into the atmosphere has been previously assumed. Firm evidence that this is indeed the case, and vehemently so, comes from the combination of satellite observations, operational weather analysis and atmospheric circulation models which the team utilised for their study.

Very likely the Gulf Stream’s direct local effects on the atmosphere are tele-connected, via planetary atmospheric waves, with weather conditions in far-away regions. How frequent and pronounced these remote responses might be is not at all clear. But it seems at least as if Gulf Stream-driven atmospheric dynamics over the North Atlantic have a marked influence on hemisphere-wide climatology.

This, you’ve guessed it, adds another piece to the climate change puzzle. Come what may, the Gulf Stream will not ‘run dry’. But its strength does vary, and a possible weakening of the Atlantic overturning circulation, to which it belongs, is unlikely to leave the Gulf Stream unaffected.

A new ice age will not come over Europe because of that, but storm tracks and rainfall patterns could be affected in rather unpredictable ways.

Quirin Schiermeier

You can vote or comment on the importance of the new Gulf Stream paper in the Journal Club of Nature Reports Climate Change.

Comments

  1. Report this comment

    xefer said:

    “It is common knowledge – and true – that the British Isles and Scandinavia enjoy a much warmer climate than Newfoundland or Labrador thanks to the Gulf Stream.”

    This recent article claims that this is a common misconception and is in his words “absolutely wrong”:

    http://www.americanscientist.org/template/AssetDetail/assetid/51963

    The author shows convincingly that it is purely an artifact of airflow across the ocean, and that the same effect can be seen in the Pacific even though the Gulf Stream’s analogue, the Kuroshio Current, conducts almost no heat to that region.

    The author states: “The Gulf Stream indeed contributes to Europe’s warmth, but it is wrong to conflate the climate difference across the North Atlantic with the northward flow of warm water in the Gulf Stream. This erroneous logic leads to such statements as (from The Times of London): ‘The British Isles lie on the same latitude as Labrador on the East Coast of Canada, and are protected from a similarly icy climate by the Atlantic conveyor belt.’ Such claims are absolutely wrong.”

  2. Report this comment

    ArndB said:

    To test how much the “Gulf Stream-driven atmospheric dynamics over the North Atlantic have a marked influence on hemisphere-wide climatology”, one need only to go back to the winter 1918/19 when temperatures exploded suddenly at the Norwegian archipelagos Spitsbergen at ca 78 degrees North, and the winter warming sustained until winter 1939/40, in detail at: http://www.arctic-warming.com/. As the northern North Atlantic is ice covered from Iceland to Bear Island, except a narrow tongue along Spitsbergen up to the Arctic Ocean during the late winter season (see graph at reference website), the arctic warming 90 years ago, can only have been generated by the northern arm of the Gulf Stream that passes Spitsbergen in the West, and keep a small section of the sea ice free up to latitude 80 degrees North. Explaining the sudden warming would enhance understanding the role of the Gulf Stream on climate change issues during the last century. In a WMO Study from 1997 V.F. Zakharov (FN) asked very clear question concerning the Arctic Climate System: (1) Why are the maximum climate fluctuations confined to the Atlantic sector of the Arctic?” (2) Why are these fluctuations pronounced, first of all, right here?” (3) Should the Atlantic sector of the Arctic be considered as a centre of some kind, a source of climate changes over the Hemisphere?”. When will they be answered?

    (FN) Zakharov, V.F.; 1997, ‘Sea Ice in the Climate System’, Arctic Climate System Study, WMO/TD-No. 782, p. 70

  3. Report this comment

    Chip Knappenberger said:

    Perhaps your link to Bryden et al. should also have included a link to the follow-up which suggested that Bryden et al.‘s results were a bit premature. You wouldn’t want to leave your readers with a false impression as to the best science of what was really happening.

    -Chip Knappenberger

  4. Report this comment

    ArndB said:

    Reply to: #4, Maurizio Morabito

    (1) The claim that the Gulf Stream is wind driven is weak: Even wind with hurricane force does not have any direct effect lower than 50 metres below the sea surface.

    (2) The claim that the Gulf Stream does not provide milder weather to Northern Europe than North American regions at similar latitudes can easily be dismissed by comparing summer and winter temperatures, and when paying attention to the extraordinary Arctic Warming from winter 1918/19 to winter 1939/40, as explained at: http://www.arctic-warming.com

Comments are closed.