1. 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 Background: What is the Conveyor

2. Could the Ocean Conveyor Come to a Halt?

3. How Could it Stop? Enough fresh water must enter the ocean until it hits a critical desalinization point. The Ocean Conveyor’s overturning is based on density As we know, the density is based on the water’s 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?

4. 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 21 st century

5. 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 wouldn’t be as drastic because: -Less ice cover in Canada and Greenland -Higher global temperature (Broecker 1999)

7. 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)