The Atlantic Ocean’s current system, an engine of the Northern Hemisphere’s climate, could be weakening to such an extent that it could soon bring big changes to the world’s weather, a scientific study said on Thursday.
The new study by Niklas Boers, published on Thursday in Nature Climate Change, suggests the Atlantic Meridional Overturning Circulation (AMOC) may have been losing stability in the course of the last century.
The study is part of the European TiPES project, coordinated by the University of Copenhagen, Denmark, and the Potsdam Institute for Climate Impact Research, Germany.
The European TIPES project (Tipping Points in the Earth System project) is a multidisciplinary effort to clarify and explain the dynamics and thresholds of climate change tipping points.
northward flow of water in the upper layers. The filled orange circles in the Nordic and
Labrador Seas indicate regions where near-surface water cools and becomes denser,
causing the water to sink to deeper layers of the Atlantic. This process is referred to as
“water mass transformation,” or “deep water formation.” In this process, heat is released
into the atmosphere. The light blue curve denotes the southward flow of cold water at
depth. Image courtesy of NOAA
Changes in the Atlantic Meridional Overturning Circulation (AMOC)
The AMOC is the key circulation system of the Atlantic Ocean. Like an engine, it moves heat from the Tropics below the equator to the Northern hemisphere by transporting warm water masses northward at the ocean surface and returning as a cool current southward at the bottom of the ocean. The Gulf Stream off the Atlantic Coast of the U.S. is part of the AMOC.
Climate models and climate records suggest the AMOC can be in two distinct modes: A strong mode, which is currently the case – and an alternative, substantially weaker mode of operation.
And based on this information, it is possible that abrupt transitions from one state to another are entirely possible. Going further, the new study suggests a collapse of the Atlantic’s current system, which is considered to be in a strong mode, would have a severe impact on global climate and weather.
However, according to the study, “Observations and recently suggested fingerprints of AMOC variability indicate a gradual weakening during the last decades, but estimates of the critical transition point remain uncertain.”
“The difference is crucial. Because the loss of dynamical stability would imply that the AMOC has approached its critical threshold beyond which an abrupt and potentially irreversible transition to the weak mode could occur,” says Boers.
“To understand this in-depth we need to find ways to improve the representation of the AMOC and polar ice sheets in comprehensive Earth system models and to better constrain their projections. I hope that the results presented here will help with that!” Boers concludes.
