Wednesday, January 9, 2008

Could Global Warming Lead to the Next Ice Age? - Shutdown of Thermohaline Circulation

(Special Report) - If you’ve seen The Day After Tomorrow or read The Coming Global Superstorm, you probably have heard of ‘thermohaline circulation’. Okay. Maybe you haven’t heard it named, but if you’ve seen the movie or read the book then you know what it is. Unconsciously. Trust me.

Basically the central theory of both mediums is that the melting ice caps will affect the salinity (AKA the amount of salt) of the oceans and currents of the world, specifically the North Atlantic Current. The North Atlantic Current is part of the Gulf Stream, which carries heat up to East North America and West Europe. And what is the North Atlantic Current (and the Gulf Stream) powered by? Thermohaline circulation. The danger is that with a desalinated current, the current could slow or even stop, and an ice age could ensue.

Okay, that’s not likely. But global warming is going to cause thermohaline circulation to slow down. This brings us to our question:

Why will global warming cause the slowdown or shutdown of thermohaline circulation?

The answer isn’t simple. I mean, it took me a whole half an hour to even begin to comprehend. How can I expect you, the anonymous reader, to understand this in the slightest?

I’ll humor you.

To understand why global warming could cause the partial shutdown of thermohaline circulation, we first have to understand how thermohaline currents work. Thermohaline currents are NOT powered by heated convection currents, unlike most currents. But we won’t get into that. Thermohaline circulation is density driven.

You have to imagine this in 3D. The current moves north along the top of the Atlantic Ocean with less density. As it moves further north, it begins to become denser. Why does it become denser? First of all, the water cools as it gets closer to the North Pole. Cold stuff is denser than hot stuff. Second, it becomes saltier as sea ice forms. Sea ice isn’t salty, so the salt gets left behind in the water. Salt, obviously, is denser than water. So now it’s denser.

And then it sinks.

Remember, this part of the current (the north flowing current) is on the top of the Atlantic. It sinks and starts heading south. All of its dense buddies are down south, and everyone wants to be at the party, right? Strange, but true. As it moves south, it loses salinity and becomes warmer. It rises, and the cycle begins again.

Can you see the problem yet?

Global warming melts the ice caps, which are made of fresh water. Fresh water means no salt, which means less dense. The fresh water will make parts of the current less dense, slowing down the current, slowing the transportation of heat. If that makes sense.

Basically, global warming will desalinize thermohaline circulation, slowing it down.

Scientists still don’t know how much of an effect the desalinization will have. Most likely it will only lead to lesser warming in far Western Europe, but further research is still needed.

But don’t worry that there’ll be an ice age. We’ve already delayed that (well technically, if ...).