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shutting down the ocean conveyor

Page history last edited by PBworks 16 years, 9 months ago

It spoke of global warming "shutting down the ocean conveyor" - the process by which the gulf stream is carried over the north Atlantic to western Europe. The judge said that, according to the Intergovernmental Panel on Climate Change, it was "very unlikely" that the conveyor would shut down in the future, though it might slow down.

 

THE TRANSCRIPT

 

Earth's Climate is an Engine

 

The earth climate is like a big engine for redistributing heat from the equator to the poles, and t does that by means of ocean current and wind current. They tell us, the scientists do, that the earth climate is a non-linear system. It's a fancy way they have of saying that the changes are not all just gradual. Some of them come suddenly in big jumps. On a world wide basis the annual average temperature is about 58 degrees Fahrenheit. If we have an increase of 5 degrees, which is on the low end of the projections, look at how that translates globally. That means an increase of only 1 degree at the equator but more than 12 degrees at the poles. So all those wind and ocean current patterns that have formed since the last ice age and have been relatively stable, they are all up in the air and they change.  And one of the ones they are most worried about where they have spent a lot of time studying the problem is in the North Atlantic where the Gulf Stream comes up and meets the cold wind coming off the arctic over Greenland and evaporates the heat out of the Gulf Stream and the steam is carried over to western Europe by the prevailing winds and the Earth's rotation, but isn't it interesting that the whole ocean current system is all linked together in this loop. They call it the ocean conveyor. And the red are the warm surface currents, the Gulf Stream is the best known of them, but the blue represents the cold currents running in the opposite direction. We don't see them at all because they run along the bottom of the ocean. Up in the North Atlantic, after that heat is pulled out, what's left behind is colder water and saltier water, because the salt doesn't go anywhere so that makes it denser and heavier. That cold, dense heavy water sinks at a rate of 5 billion gallons per second. That pulls that current back south.

 

Disruption of the Ocean Conveyor

 

At the end of the last ice age as the last glacierwas receding from North America, the ice melted and a giant pool of fresh water formed in North America, and the Great Lakes are the remnants of that huge lake. An ice dam on the eastern border formed, and one day it broke. And all that fresh water came rushing out, ripping open the St. Lawrence, there. It diluted the salty dense cold water, made it fresher and lighter so it stopped sinking. And that pump shut off and the heat transfer stopped, and Europe went back into an ice age for another 900 or 1000 years. And the change from conditions like we have here today to an ice age took place in perhaps as little as 10 years time, so that's is a sudden jump. Of course that's not going to happen again, because the glaciers of North America are not there. Is there any big chunk of ice anywhere near there? Oh yeah, (pointing at Greenland). We'll come back to that one.

 

 

 

THE JUDGMENT

 

 

3. Shutting down of the "Ocean Conveyor".

In scene 17 he says, "One of the ones they are most worried about where they have spent a lot of time studying the problem is the North Atlantic, where the Gulf Stream comes up and meets the cold wind coming off the Arctic over Greenland and evaporates the heat out of the Gulf Stream and the stream is carried over to western Europe by the prevailing winds and the earth's rotation ... they call it the Ocean Conveyor … At the end of the last ice age … that pump shut off and the heat transfer stopped and Europe went back into an ice age for another 900 or 1000 years. Of course that's not going to happen again, because glaciers of North America are not there. Is there any big chunk of ice anywhere near there? Oh yeah pointing at Greenland". According to the IPCC, it is very unlikely that the Ocean Conveyor (known technically as the Meridional Overturning Circulation or thermohaline circulation) will shut down in the future, though it is considered likely that thermohaline circulation may slow down.

 

COMMENTARY

William:

 

The IPCC assess that it is very unlikely that the “ocean conveyor” (also known as the “meridional overturning circulation” or “thermohaline circulation”) will undergo a large abrupt transition this century, although it is very likely to slow down. Most scientists would regard talk of an imminent ice-age as speculation.

 

Gore talks about this, again in a prediction-free way intended to imply trouble, but I forget his words (see para 27). The guidance is correct; Gore was probably misleading.

 

Gavin:

 

For THC, I maintain that it is something that is worth discussing, even

though I don't think it likely to stop abruptly. Gore was correct to

discuss it and frankly, at the time the movie was filmed it was not

clear that all the AR4 models only showed slowdowns. He did not say that

it would happen, nor that it was likely, merely possible.

 

mt:

 

            Again there's a problem in that the snippets come from many presentations. He discusses the Greenland ice sheet in detail but never ties it back to the THC within the movie.  So the pointing at Greenland was perhaps sloppy. Here, though, you can't find any factual error in what he said, and as Gavin says, the emphasis seems appropriate to the context.

 

 

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