Weakening ocean currents system may have disastrous climate consequences over coming decades

Published by Niall Sargent on

July 29th, 2018

Irish climate scientists have warned that the expected weakening of the ocean current circulation system that gives Ireland its mild climate may have disastrous climate consequences in coming decades.

The weakening of the Atlantic Meridional Overturning Circulation (AMOC) system could lead to “accelerated global surface warming” according to a letter published in Nature by scientists from the Irish Climate Analysis and Research Unit (ICARUS) at Maynooth University.

The letter written by Dr Gerard McCarthy and Professor Peter Thorne comes just days after a team of international scientists found that climate change doubled the likelihood of the current heatwave in Ireland.

Traditionally, strong ocean circulation is associated with higher temperatures. The letter, however, points to new research on the potential influence of weakened circulation on the surge in already rising global temperatures.

The ICARUS letter examines a recent study by Prof Xianyao Chen of the Ocean University of China and Prof Ka-Kit Tung of the University of Washington on variations in the AMOC ocean currents system.

The AMOC system stretches across the Atlantic Ocean, with one of its currents, the Gulf Stream, playing a big hand in protecting Ireland from extreme weather and gives us our wet, mild climate.

The research from Prof Chen and Prof Tung contends that a strong AMOC can store half of the heat arising from greenhouse gas concentrations in the deep waters of the North Atlantic, reducing overall global warming.

They argue, however, that a weak AMOC will result in a period of rapid global surface warming that could last for more than two decades. This is worrying according to ICARUS’s Dr McCarthy as the AMOC is very likely to weaken in the coming decades.

“[This] could have disastrous outcomes for the global climate and make navigating the challenges of global climate change even more difficult,” he warned.

The Atlantic Ocean has already experienced “muted rises in surface temperature relative to the global ocean” in the past few decades. “This relative lack of warming has been interpreted as a fingerprint of AMOC decline,” he said.

“Whether AMOC observatories will document the predicted decline remains to be seen, but they have already observed that the AMOC is in a weakened state and the Atlantic is surprisingly cold suggesting that it is not effectively storing heat in its lower levels.”

McCarthy and Thorne argue that Professors Chen and Tung’s research may also hold the key to explaining the 15 year hiatus period between 1999 and 2013 where the steady rise in global surface temperatures over the previous 20 years slowed before accelerating rapidly again between 2014 and 2017.

The AMOC was “robust and increasing in strength” during the hiatus period and could effectively transfer heat far beneath the ocean, and may explain the reduction in global warming, the ICARUS team argues.

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Niall Sargent

Niall is the Editor of The Green News. He is a multimedia journalist, with an MA in Investigative Journalism from City University, London