The Gulf Stream - Is It Collapsing?

I know I tend to sound a bit like a Cassandra about Climate Change, but everything I have talked about (okay almost everything) is either happening or beginning to happen. The current freakout is hitting news this week all over. You might have seen it (otherwise a quick google search will take you to it).

One of the worst things, and I have talked about this before, is the possible collapse of the Gulf Stream (part of the Atlantic Meridional Overturning Circulation). Here is a map of the Gulf Stream and why it may be civilization changing if it collapses altogether.

The Gulf Stream takes very warm water from Caribbean ( starting actually off the coast of tropical Africa before the Gulf of Mexico) and moves it up the East Coast of the United Staes, delivering relatively warm water to Western Europe. This effects many things:

1. It keeps most of Northwestern Europe habitable. This includes the British Islands, France, the low countries, Denmark and Norway - even Iceland - where the Gulf Stream raises temperatures of the ocean, which effects the land.
2. It keeps the Atlantic Provinces of Canada relatively warm (relative to their latitude).
3. It keeps hurricanes moving both up the Atlantic Coast and in the Caribbean.
4. It supports fisheries in the European North Atlantic and the North Sea.

So if the Gulf Stream slows down - as predicted and now beginning to occur - we will see some major changes. 

We have already seen hurricanes lasting longer, because they are pushed along less by the slower current. As the hurricanes move more slowly up the east, devastation is worse. Also, since the Gulf waters move slower, the water gets warmer allowing hurricanes to gain much more strength and water. We saw the effect of this in major Houston flooding a few years ago. Warm air lets more water vapor to be held (and then dropped). If the Gulf Stream doesn't move water out of the Caribbean and Gulf of Mexico as quickly, the Gulf and Caribbean waters heat up more.

The effect on weather in Europe is a much more complex system. Cooler, slower water means less ocean heat to Northern Europe, but it is offset - in ways we don't understand yet - by warmer air currents on the continent.

There are many reasons the Gulf Stream is slowing, most we don't understand. As CNN said, you can't to a study on the Gulf Stream because we don't have another Gulf Stream to compare the steady state against. We tend to only see the effects either as they occur or afterwards.

One major effect that we can predict however is less a current "slowing" and more of an abrupt end. That would happen (and might be happening now) if Greenland starts to melt much quicker. As the snow and glaciers melt quicker, they release more cold water, That water travels south (via currents) to the Gulf Stream from the East and West sides of Greenland. This will cool the water, damping the effect of the Gulf Stream via two paths.

First, the cold water will slowly cool the Gulf Stream by diluting it with very cold fresh water water. This is obvious, and may effect Europe over time.

Second, and less obvious, the temperature differential now keeps the warm  Gulf Stream current above the colder deep Atlantic water. This temperature differential allows it move the warm water relatively quickly over the much colder lower Atlantic ocean. But once cold Arctic Fresh water is allowed to mix, the Gulf Stream sinks deeper into the Atlantic and moves slower.

And we are seeing Greenland melt occurring more rapidly each year. It may hit a "tipping point" where the lose of white snow, replaced by temporary lakes or newly dry land, increases the melt speed exponentially. (Glaciers reflect a lot more snow than land or lakes.) 

We know this will, in the United States, increase the power of hurricanes, while slowing them down and drenching areas quickly. It will also increase the heat in Atlantic Seaboard states.

The answer is definitely to try and reduce carbon emissions, but since we are too late to stop most changes, we will have to build for more intense hurricanes and a sea level rise. US sea levels will rise not only because of expanding water, but back up in moving this water away from the United States.