Background: What is the Conveyor

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Background What is the Conveyor

• Warm currents travel north, cooling and thus
  becoming denser.
• The denser water sinks, and the force of the
  sinking causes the water to run under the surface
  towards the equator.
• This process heats much of the Northern
  Hemisphere.
• Thermohaline Circulation is bistable, meaning it
  can switch between an on position and an off
  position

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Could the Ocean Conveyor Come to a Halt?
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How Could it Stop?

• Enough fresh water must enter the ocean until it
  hits a critical desalinization point.
• The Ocean Conveyors overturning is based on
  density
• As we know, the density is based on the waters
  salinity and temperature, so an influx of fresh
  water could stop the overturning.
• This fresh water would come from melting glaciers
  and river runoff
• Fresh water has increased in the North Atlantic
  by 4,000 cubic kilometers since the 1960s--what
  does this mean for the Ocean Conveyor?

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• IPCC
• No evidence that there has been a change in the
  meridional overturning circulation
• There has been significant freshening in the
  North Atlantic, which can be attributed to
  melting sea ice however, not enough freshening
  to halt the ocean conveyor
• Response to experiment by Harry Bryden
• Bryden probed the ocean at a period of relatively
  low circulation
• Found a 30 decrease in overturning rate
• Scientist Quirin Schiermeier writes in Nature
  magazine that there is inconclusive evidence for
  a shutdown of the circulation
• RAPID will help us to detect changes in the
  future and build evidence
• RAPID
• RAPID is a new program that measures changes in
  the rate of overturning in the North Atlantic
• Can it shut down?
• Scientists believe there would need to be 4-5
  degrees of global warming temperature increase to
  cause enough melt to halt the circulation
• Ice continues to melt at faster rates
• If this continues, we are looking at a slowdown
  of the conveyor
• 25 slowdown by the end of the 21st century

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Effects on Europe

• Abrupt Climate Change in the past caused by
  Thermohaline Circulation shutdown Younger Dryas
• Temp. in Europe dropped around 10 degrees Celsius
• This time it wouldnt be as drastic because
• -Less ice cover in Canada and Greenland
• -Higher global temperature
• (Broecker 1999)

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Effects on New York

• In the event of a THC shutdown, New York would
• -Experience flooding
• -Have to cope with water and food rationing from
  megadroughts
• -See vastly depleted wetlands
• (Marsh 2004)
• (Schwartz and Randall 2003)