Note that we pick AMOC as a representative example of the wider ocean circulation impacts, about which uncertainty is important. The metric here can be rephrased more succinctly as SAI is under-effective by 50%. GHG-driven climate change causes a decrease in magnitude of negative heat flux in the North Atlantic, contributing to a weakening of the downwelling branch of AMOC. SAI can potentially mitigate this, along with other factors contributing to AMOC decline such as decreasing salinity and decreasing Arctic sea ice. SAI will likely "under-compensate" AMOC relative to global mean temperature, but unclear by how much. The tipping behavior (and hysteresis) of AMOC means this metric is sensitive to when SAI is deployed. There may be scenarios when a late deployment cannot restore an already "tipped" AMOC. Complex set of factors that impact AMOC make it harder to draw clear conclusions; future AMOC state has significant uncertainty without SAI. Response with SAI also depends on latitude(s) of deployment.
Metric
AMOC strength at 0.5C cooling remains closer (weaker) to where it would have been without SAI, than it is to the (historical) level when global mean temperature was the same (as the 0.5°C cooler world).
Uncertainty
Uncertainty is mostly derived from which SAI strategy is chosen and the magnitude of the benefit for AMOC.
Decision relevance
There is no evidence to suggest that (hemispherically balanced) SAI would decrease the strength of AMOC, the question is instead the extent to which it can help, and under which temporal pathways.