Warming increased in 2020 when sulfur was eliminated from fuel for ships that cross the oceans, thereby reducing brightness of marine clouds.
Tianle Yuan and ten others
May 30, 2024

Funded by NASA, eleven US scientists examined the effects on low clouds over the oceans from the reduction in sulfur in ship fuels that began enforcement in 2020.  They concluded that, before 2020, sulfur in ship fuels significantly cooled the planet by injecting into the lower atmosphere cloud condensation nucleating sulfur particles which brightened marine clouds which reflected sunlight to space.  The above image shows the locations and relative magnitude of that cooling.  

The authors concluded that the rate of warming of the Earth significantly increased after 2020 to roughly double the rate of warming from1980 to 2020 and that the loss of the former cooling effect from sulfur in ship fuels caused about 80% of that increased rate of warming.

This study suggests that, if we can mount equipment on ships that again puts cloud condensation nucleating particles into ship exhaust, it will significantly slow global warming. Research is underway to determine if those particles can simply be sea salt taken from the ocean.  Sea salt particles are normally in the air over the oceans and they constantly blow onto the land.  The trick is to sufficiently increase the number of particles of the right size and loft them high enough.

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