Shutdown of circulation pattern could be disastrous, researchers say

Dec 13, 2004

If global warming shuts down the thermohaline circulation in the North Atlantic Ocean, the result could be catastrophic climate change. The environmental effects, models indicate, depend upon whether the shutdown is reversible or irreversible.

“If the thermohaline shutdown is irreversible, we would have to work much harder to get it to restart,” said Michael Schlesinger, a professor of atmospheric sciences at the University of Illinois at Urbana-Champaign and a co-author of a report to be presented at the American Geophysical Union meeting in San Francisco, Dec. 13-17. “Not only would we have the very difficult task of removing carbon dioxide from the atmosphere, we also would have the virtually impossible task of removing fresh water from the North Atlantic Ocean.”

The thermohaline circulation is driven by differences in seawater density, caused by temperature and salinity. Like a great conveyor belt, the circulation pattern moves warm surface water from the southern hemisphere toward the North Pole. Between Greenland and Norway, the water cools, sinks into the deep ocean, and begins flowing back to the south.

“This movement carries a tremendous amount of heat northward, and plays a vital role in maintaining the current climate,” Schlesinger said. “While shutting it down due to global warming would not cause an ice age, as was depicted in a recent blockbuster movie, ‘The Day After Tomorrow,’ eastern North America and western Europe would nevertheless experience a shift in climate.”

Paleoclimate records constructed from Greenland ice cores have revealed that the thermohaline circulation has, indeed, shut down in the past and caused regional climate change. As the vast ice sheet that covered much of North America during the last ice age finally receded, the meltwater flowed out the St. Lawrence and into the North Atlantic.

“The additional fresh water made the ocean surface less dense and it stopped sinking, effectively shutting down the thermohaline circulation,” Schlesinger said. “As a result, Greenland cooled by about 7 degrees Celsius within several decades. When the meltwater stopped, the circulation pattern restarted, and Greenland warmed.”

Since the system has previously shut down by itself, “it is not unlikely that it will do so again, especially with our help in pouring greenhouse gases into the atmosphere,” Schlesinger said. “Higher temperatures due to global warming could add fresh water to the northern North Atlantic by increasing the precipitation and by melting nearby sea ice, mountain glaciers and the Greenland ice sheet. This influx of fresh water could reduce the surface salinity and density, leading to a shutdown of the thermohaline circulation.

Schlesinger and his team simulated the potential effects with an uncoupled ocean general circulation model and with it coupled to an atmosphere general circulation model. They found that the thermohaline circulation shut down irreversibly in the uncoupled model simulation, but reversibly in the coupled model simulation.

“The different results occurred because of a crucial feedback mechanism that appeared only in the coupled model simulation,” Schlesinger said. “Enhanced evaporation increased the salinity and density of the ocean surface, offsetting the effects of additional fresh water.”

“The irreversible shutdown of the thermohaline circulation thus appears to be an artifact of the model, rather than a likely outcome of global warming,” Schlesinger said. “But, because the possibility of an irreversible shutdown cannot be excluded, suitable policy options should continue to be explored. Doing nothing to abate global warming would be foolhardy if the thermohaline circulation shutdown is irreversible.”

Coauthors are U. of I. graduate student Jianjun Yin, research specialist Natasha Andronova, research programmer Bin Li, and Princeton University researcher Sergey Malyshev. The National Science Foundation funded the work.

Source: University of Illinois at Urbana-Champaign

Explore further: CubeSat instruments to demonstrate NASA firsts

add to favorites email to friend print save as pdf

Related Stories

Polar storms spur ocean circulation

Dec 16, 2012

Though it seems like an oxymoron, Arctic hurricanes happen, complete with a central "eye," extreme low barometric pressure and towering 30-foot waves that can sink small ships and coat metal platforms with ...

Eddies drive section of thermohaline circulation

Jul 06, 2012

(Phys.org) -- Giant currents that traverse the world’s oceans may not be as stable as previously thought after researchers found a branch of one of these global currents was powered and steered entirely ...

How the Pacific Ocean leaks (w /Video)

Apr 17, 2012

A state-of-the-art ocean model has been used in a new study to conduct the first detailed investigation of oceanic water flow between the Pacific and Indian Oceans via the south of Australia. 

Recommended for you

Time in space exposes materials to the test of time

3 hours ago

Much like that pickup truck rusting in your backyard thanks to time, rain and the elements, extended stays in the brutal environment of space can take its toll on spacecraft, satellites and space stations. ...

Image: Hubble captures the Egg Nebula

5 hours ago

This colourful image shows a cosmic lighthouse known as the Egg Nebula, which lies around 3000 light-years from Earth. The image, taken with the NASA/ESA Hubble Space Telescope, has captured a brief but dramatic ...

Earth's orbit around the sun

6 hours ago

Ever since the 16th century when Nicolaus Copernicus demonstrated that the Earth revolved around in the Sun, scientists have worked tirelessly to understand the relationship in mathematical terms. If this ...

How can we search for life on icy moons such as Europa?

6 hours ago

Our solar system is host to a wealth of icy worlds that may have water beneath the surface. The Cassini spacecraft recently uncovered evidence of a possible ocean under the surface of Saturn's moon, Mimas.

CubeSat instruments to demonstrate NASA firsts

7 hours ago

The Dellingr six-unit CubeSat, which is taking its developers just one year to design, build and integrate, won't be the only potentially groundbreaking capability for NASA. Its heliophysics payloads also ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.