Thermohaline circulation in the world's oceans. Graphic: Earth Institute

By Renee Cho
6 June 2017

(Earth Institute) – The 2004 disaster movie, The Day After Tomorrow, depicted the cataclysmic effects—superstorms, tornadoes and deep freezes— resulting from the impacts of climate change. In the movie, global warming had accelerated the melting of polar ice, which disrupted circulation in the North Atlantic Ocean, triggering violent changes in the weather. Scientists pooh-poohed the dire scenarios in the movie, but affirmed that climate change could indeed affect ocean circulation—could it shut down the Gulf Stream?

The many ocean currents and wind systems that move heat from the equator northwards towards the poles then transport the cold water back towards the equator make up the thermohaline circulation. (Thermo refers to temperature while haline denotes salt content; both factors determine the density of ocean waters.) It is also called the Great Ocean Conveyor, a term coined in 1987 by Wallace Broecker, Newberry Professor of Geology in the Department of Earth and Environmental Sciences at Columbia University and a scientist at Lamont-Doherty Earth Observatory. Broecker theorized that changes in the thermohaline circulation triggered dramatic changes in the North Atlantic during the last ice age. […]

As the planet warms, more and more fresh water is entering the system. In 2016, the extent of Greenland’s melting sea ice set a new record low. That May, the Arctic lost about 23,600 square miles of ice daily, compared to the long-term average loss of 18,000 square miles per day. A study by Marco Tedesco, a research professor at Lamont-Doherty specializing in Greenland, and colleagues suggested that a reduction in the temperature difference between the polar and temperate regions (the Arctic is warming twice as fast as the rest of the planet) pulled the jet stream air currents northwards. The warm moist air it carried hovered over Greenland, causing the record melting.

So far this year, Tedesco said, “The melting in Greenland is within the mean, but it’s still above the average of what was happening 20 years ago…The snow melt from Siberia has also been melting sooner, there’s been more fresh water from Greenland, there’s more fresh water from sea ice in the Arctic Ocean and more fresh water from North Canada which has been melting at an increasing rate. All these factors are pointing in the direction of increasing the freshwater discharge in the North Atlantic section of the Arctic. It’s very likely going to have an impact.” [more]

Could Climate Change Shut Down the Gulf Stream?

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