Initially, because of the large amount of water vapor injected into the atmosphere, the Tonga eruption was seen as a warming event, but now it appears because of the aerosols in the stratosphere, there will be net cooling.
This happened in the Southern Hemosphere so it will take time for the effects to reach here.
I don’t know how this will shake out, and I doubt anyone else does either. It will depend on which lasts longer, the water vapor or the aerosols. In the long run, oceans are cooled or warmed by changes in radiation, not air temperature, so in the long run I suspect this will reset us downward, dwarfing CO2 effects, for decades.
But the effects on clouds are the real wild card.
Tidewater News and Opinion Forum 
Very interesting article, I had not heard that it was so large. Its effects appear to be mainly in the southern hemisphere, even after a year. Will be interesting to see how sea water temperatures that are routinely tracked change based on this.
However, even the article says: “Even after the spring of 2023, we can count on continued noticeable effects on temperature and agriculture at least into 2025.” So maybe not decades.
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