Could an Ice Age depicted in the 2004 movie “The Day After Tomorrow” be soon upon us?
According to a new study by researchers at the Potsdam Institute for Climate Impact Research, we are witnessing a slowdown of the great ocean circulation that drives the Gulf Stream current off the US east coast.
What does it mean and how could it affect us? Let's find out.
The Global Conveyor Belt
Connecting the oceans of the world is a deep-water current known as the global conveyor belt. This flow (see notes) is driven by the density difference in the water and is sometimes referred to as the thermohaline circulation because the movement of water is dependent on its temperature (thermo) and salinity (haline).
In the case of the Gulf Stream, warm water from the tropics travel along the Gulf of Mexico, up the eastern shores of the US, and eventually veers off eastward to split into what is called the North Atlantic current. It carries warm waters to the western shores of Europe acting as a heat pump to lessen the intensity of the cold in Europe. Eventually, when the current encounters cold water from melting polar ice caps, the cold salty water sinks because of its density and travels back southward.
But this flow may be changing.
The key to the North Atlantic current is the fact that cold salt water is denser than warm water and it sinks. However, global warming is increasing the glacial melt in the North Pole and Greenland. The increase in freshwater would dilute the salinity of ocean water -- making it less dense and reducing its tendency to sink. Too much more of melting can eventually shut down the circulation.
The slowdown in the circulation will result in rising sea levels. Especially vulnerable are cities such as New York and Boston. This is because warm water tends to expand, and this is true of the Gulf Stream flowing northwards along the US East Coast. And indeed, researchers have found a 4-inch rise in sea level along the US East Coast in 2009 and 2010.
Joining the Dots
To help them explain their hypothesis, scientists reconstructed sea surface temperatures in the North Atlantic. They noticed surface temperatures began weakening around 1970, but temporarily recovered in the 1990s.
Meanwhile, global temperatures have been on the rise during the past few winters around the world. The region on the North Atlantic just south of Greenland, between Canada and Britain has actually been becoming colder – an indicator of less northward heat transport. And though circulation has weakened by about 15 to 20 percent, nothing like this has happened in over 1000 years!
While scientists have worried about polar ice melting and its effect on sea level rise, its pace has been faster than previously expected. One thing scientists know of sure -- shutting down of this circulation will almost certainly affect global weather, maybe not dramatic enough to cause an Ice Age.