Thread by @geoengineering1

🚨Can aeosols counter AMOC collapse?

A NEW study suggests Stratospheric Aerosol Injection (#SAI) could help prevent the decline of the Atlantic Meridional Overturning Circulation (#AMOC), but only if aerosols are injected in the appropriate latitude & hemisphere.

DETAILS🧵1/12

2/ The AMOC is a key component of Earth’s climate system, transporting heat and nutrients across the Atlantic.

Its decline, already underway, is projected to accelerate under global warming, possibly approaching a tipping point this century.

3/ Using CESM2(WACCM6), Bednarz et al. ran sensitivity experiments with SO₂ injections at latitudes from 45°S to 45°N.

Each scenario injected 12 Tg-SO₂/yr (2035–2069) to test how SAI location affects AMOC stability.

4/ Results

SAI in the Southern Hemisphere produced little impact on AMOC, despite achieving global cooling.

Equatorial injections stabilized AMOC at nearly constant strength.

Northern Hemisphere injections restored AMOC to 2020 levels by 2070, counteracting GHG-driven decline

5/ The mechanism lies in North Atlantic surface processes.

Northern Hemisphere SAI enhances heat loss from the ocean to the atmosphere, cooling surface waters and making them denser.

This promotes deepwater formation and strengthens the overturning circulation...

6/ By contrast, Southern Hemisphere injections do not alter North Atlantic densities sufficiently, leading to weak or absent AMOC recovery.

7/ Furthermore, this study show that different processes play different roles in determining the AMOC response between the initial (∼10–15 years) and longer timescales.

8/ In the early years (~10-15yrs), AMOC responds mainly to SAI-induced direct cooling. Less sunlight reaches the surface, oceans lose more heat to the atmosphere, and extra sea-ice forms. These processes make North Atlantic waters denser, boosting overturning circulation.

9/ Over decades, the AMOC itself becomes a driver. Once circulation strengthens or weakens, it reshapes salt transport and ocean heat flow.

These feedbacks “lock in” the new AMOC state, keeping it relatively stable across different NH injection latitudes.

10/ But study cautions that injecting aerosols in only one hemisphere is inadvisable, as it may disrupt monsoons and create dangerous interhemispheric imbalances.

11/ These experiments were idealized, designed to isolate mechanisms, not to propose strategies.

They show SAI could in principle help avoid some tipping points, but outcomes depend strongly on how SAI is done. A deeper, process-based understanding remains essential.

For more details, read the study entitled "Stratospheric Aerosol Injection Could Prevent Future Atlantic Meridional Overturning Circulation Decline, But Injection Location is Key" here:


🧵12/12 #geoengineering #SAIagupubs.onlinelibrary.wiley.com/doi/10.1029/20…

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