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Effect of Global Warming on World’s Ocean Circulation – an unknown quantity

A single Atlantic Ocean current system accounts for up to a quarter of the planet’s heat flux.

For now, everyone awaits more data to see whether the AMOC is slowing down and, if so, what that will mean for the planet

How Climate Change Could Jam The World’s Ocean Circulation, 06 SEP 2016: ANALYSIS Scientists are closely monitoring a key current in the North Atlantic to see if rising sea temperatures and increased freshwater from melting ice are altering the “ocean conveyor belt” — a vast oceanic stream that plays a major role in the global climate system.

Environment 360, by nicola jones Susan Lozier is having a busy year. From May to September, her oceanographic team is making five research cruises across the North Atlantic, hauling up dozens of moored instruments that track currents far beneath the surface. The data they retrieve will be the first complete set documenting how North Atlantic waters are shifting — and should help solve the mystery of whether there is a long-term slowdown in ocean circulation. “We have a lot of people very interested in the data,” says Lozier, a physical oceanographer at Duke University.

A similar string of moorings across the middle of the Atlantic, delving as deep as 3.7 miles from the Canary Islands to the Bahamas, has already detected a disturbing drop in this ocean’s massive circulation pattern. Since those moorings were installed in 2004, they have seen the Atlantic current wobble and weaken by as much as 30 percent, turning down the dial on a dramatic heat pump that transports warmth toward northern Europe. Turn that dial down too much and Europe will go into a deep chill. 

Researchers have been worried about an Atlantic slowdown for years. The Atlantic serves as the engine for the planet’s conveyor belt of ocean currents: The massive amount of cooler water that sinks in the North Atlantic stirs up that entire ocean and drives currents in the Southern and Pacific oceans, too. “It is the key component” in global circulation, says Ellen Martin, a paleoclimate and ocean current researcher at the University of Florida. So when the Atlantic turns sluggish, it has worldwide impacts: The entire Northern Hemisphere cools, Indian and Asian monsoon areas dry up, North Atlantic storms get amplified, and less ocean mixing results in less plankton and other life in the sea.

If the North Atlantic current slows dramatically, then the entire Northern Hemisphere would cool; a complete collapse of the current could even reverse global warming for about 20 years. But the heat that ocean currents fail to transport northwards would make parts of the Southern Hemisphere even hotter. And a cooler north isn’t necessarily good news.

The jury is still out. Weakening is a possibility, but it hasn’t been proven yet,’ says one scientist.

Should the AMOC shut down, models show that changes in rainfall patterns would dry up Europe’s rivers, and North America’s entire Eastern Seaboard could see an additional 30 inches of sea level rise as the backed-up currents pile water up on East Coast shores.

But to pin down what the AMOC is going to do, researchers need to better understand what it’s doing right now. And that is proving tricky. ………

September 9, 2016 - Posted by Christina Macpherson | 2 WORLD, climate change