Grave Early Warning Observational Signs for Pending Near-Term AMOC Ocean Circulation System Collapse
I delve into the details of a new paper on the risks of a pending AMOC (Atlantic Meridional Overturning Circulation) tipping from the present strong mode to a new weak mode. If the present AMOC shuts down and a new, weaker state is established there will be enormous consequences to society and Earth’s ecosystems.
I use Earth NullSchool and Climate Reanalyzer to examine to present state of the surface ocean currents and Sea Surface Temperature (SSTs) and examine recent scientific evidence that the AMOC is at its weakest state in 1600 years, and that there is observational evidence that the slowing in the last decade has accelerated, and we may in fact be on the brink of a system shutdown and reconfiguration.
When a highly complex nonlinear system approaches a tipping point threshold, the system variability often increases and there is a “critical slowing down” in the frequency components of the system. Essentially, the system loses elasticity and resiliency and becomes rigid and brittle, and then shatters or breaks and enters a new, often irreversible state.
We are seeing this increased variability and critical slowing down in both the sea surface temperature and sea surface salinity in the critical locations that drive the thermohaline circulation system. It seems that a tipping point to a new ocean circulation system, with slower ocean currents and lower latitude loops may occur in the near term future.
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Ref 1: A major Atlantic current is at a critical transition point, by Kara Norton. Feb 17, 2022
Around 15,000 years ago, the Earth began to transition from a state of heavy glacial coverage to a period of warming. As temperatures rose, large ice sheets that once blanketed much of North America and Europe thawed, and the oceans began to rise.
But after 2,000 years of warming, the Earth abruptly cooled to near-glacial conditions. And it stayed that way for more than a thousand years.
Scientists have long debated how this abrupt climatic event, which they call the Younger Dryas, occurred. This question has become an urgent one as some researchers think an abrupt climatic event could happen again and disrupt the Gulf Stream, the forceful ocean current that transports warm water from the Gulf of Mexico up North America’s Northeast coast.
An analysis published in the journal Nature Climate Change in August found that the larger system that the Gulf Stream is part of, called the Atlantic Meridional Overturning Circulation (AMOC), is approaching a tipping point.
Over the last century, this ocean circulation system has “moved closer to a critical threshold, where it may abruptly shift from the current, strong circulation mode to a much weaker one,” says study author Niklas Boers, a climate researcher at the Potsdam Institute for Climate Impact Research in Germany.
Ref 2: Climate crisis: Scientists spot warning signs of Gulf Stream collapse, 05 Aug, 2021
Climate scientists have detected warning signs of the collapse of the Gulf Stream, one of the planet’s main potential tipping points.
The research found “an almost complete loss of stability over the last century” of the currents that researchers call the Atlantic meridional overturning circulation (AMOC). The currents are already at their slowest point in at least 1,600 years, but the new analysis shows they may be nearing a shutdown.
Ref 3: Current Atlantic Meridional Overturning Circulation weakest in last millennium, Caesar, McCarthy, Thornalley, Cahill, Rahmstorf, 25 Feb, 2021
The Atlantic Meridional Overturning Circulation (AMOC)—one of Earth’s major ocean circulation systems—redistributes heat on our planet and has a major impact on climate. Here, we compare a variety of published proxy records to reconstruct the evolution of the AMOC since about AD 400. A fairly consistent picture of the AMOC emerges: after a long and relatively stable period, there was an initial weakening starting in the nineteenth century, followed by a second, more rapid, decline in the mid-twentieth century, leading to the weakest state of the AMOC occurring in recent decades.
Ref 4: Observation-based early-warning signals for a collapse of the Atlantic Meridional Overturning Circulation, Niklas Boers, 05 Aug, 2021
The Atlantic Meridional Overturning Circulation (AMOC), a major ocean current system transporting warm surface waters toward the northern Atlantic, has been suggested to exhibit two distinct modes of operation. A collapse from the currently attained strong to the weak mode would have severe impacts on the global climate system and further multi-stable Earth system components. 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.
Here, a robust and general early-warning indicator for forthcoming critical transitions is introduced. Significant early-warning signals are found in eight independent AMOC indices, based on observational sea-surface temperature and salinity data from across the Atlantic Ocean basin. These results reveal spatially consistent empirical evidence that, in the course of the last century, the AMOC may have evolved from relatively stable conditions to a point close to a critical transition.
Paul Beckwith, Climate System Scientist 