How AMOC Slowdown Greatly Reduces Carbon Uptake Accelerating GHG & Global Warming Costing $Trillions
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Max Planck Institute for Meteorology: Weaker ocean circulation could cost trillions
https://mpimet.mpg.de/en/communication/news/weaker-ocean-circulation-could-cost-trillions
Climate Visualization Laboratory YouTube: Following the upper and lower limbs of the AMOC (Atlantic Meridional Overturning Circulation)
With large incoming solar radiation in tropical regions, upper layers of the Atlantic Ocean gain heat at low latitudes. Ocean currents are set in motion to re-distribute heat to higher latitudes, warming up the atmosphere along their path and contributing to mild weather conditions over Europe. This corresponds to the upper limb of the Atlantic meridional overturning circulation - AMOC.
At high latitudes, the cooled and densified surface waters go deeper and return back south, making up the lower AMOC limb. We can track water movement by visualizing particles. Length of particle trails is proportional to the velocity of the ocean current and their color to the ocean temperature. Vigorous warm currents flow North along the western Atlantic boundary. The North Brazil Current, breaks up into strongly rotating circular eddies, then feeds flow into the Caribbean. Away from boundaries, particle trails are shorter, meaning weaker velocities. Gulf of Mexico current makes a sharp turn into the Florida Straits adding to one of the largest current systems in the World: the Gulf Stream. Energetic eddies rotate for a long time around their centers. Some currents escape the eddies and flow east, continuing in the Azores Current and some move North. Further north, the Gulf Stream continues as the weaker less defined North Atlantic Current.
Some flow continues to Nordic Seas then partially recirculates in the subpolar north Atlantic, into the Labrador Sea. Surface waters lose some of the heat and become cold thus dense. In the Labrador Sea, harsh winter conditions make the surface water even colder and denser so it is heavier than water below so it sinks deeper. Once at depths around 1000 to 2000 meters, it encounters water of similar densities and flows south. Below 2000 meters depth the so-called Deep Western Boundary Current forms lower AMOC limb, starting at the southern tip of Greenland following the continental slope. At the exit of the Labrador Sea, it goes around Flemish Cap and enters region below the Gulf Stream.
Flow in upper layers is so strong that currents deeper than 2000m feel movement and are entangled into eddies. Directly at the boundary, currents progress slowly southwards. Flow below 2000m south from Gulf Stream eddy region is mostly confined to continental slope and follows bottom topography. Along South America, the continental slope is interrupted by large underwater promontories which the Deep Western Boundary Current circumvents. Meanders and eddies are generated; flow gets unstable. Flow is disrupted into eddies and no longer flows as a well-defined current. Lower limb of the AMOC becomes dominated by ocean eddies.
Video link: https://www.youtube.com/watch?v=U9cal-dFjx0
Peer-reviewed scientific paper: Weakening AMOC reduces ocean carbon uptake and increases
the social cost of carbon
Abstract
A weakening of the Atlantic Meridional Overturning Circulation (AMOC) has been found to be globally beneficial by economic assessments. This result emerges because AMOC weakening would cool the Northern Hemisphere, thereby reducing expected climate damages and decreasing estimates of the global social cost of carbon dioxide (SCC). There are, however, many other impacts of AMOC weakening that are not yet taken into account. Here, we add a second impact channel by quantifying the effects of AMOC weakening on ocean carbon uptake, using biogeochemically-only coupled freshwater hosing simulations in the Max Planck Institute Earth System Model. Our simulations reveal an approximately linear relationship between AMOC strength and carbon uptake reductions, constituting a carbon cycle feedback that leads to higher atmospheric CO2 concentrations and stronger global warming. This AMOC carbon feedback, when incorporated into an integrated climate-economy model, leads to additional economic damages of several trillion US dollars and raises the SCC by about 1%. The SCC increase is similar in magnitude, but of opposite sign, to the SCC effect of Northern Hemisphere cooling. While there are many other potentially relevant economic impact channels, the AMOC carbon feedback alone could thus flip the consequences of AMOC weakening into a net cost to society.
https://www.pnas.org/doi/pdf/10.1073/pnas.2419543122
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