[sixbrx]

That mirrors global average temperature in general for that time period. Apparently it was because we were pumping sulfates into the atmosphere at an amazing rate from the 1940's until the EPA was born. Sulfates block sunlight and so mask the overall warming, at the cost of polluting the atmosphere.

See for example: https://www.sciencenews.org/article/50-years-ago-scientists-...

[gary_0]

It has been proposed to intentionally resume injecting sulfates into the upper atmosphere in order to mitigate global warming[0]. (This is a horrible idea, but the jury's still out on whether it's better than the alternative.)

[0] https://en.wikipedia.org/wiki/Solar_geoengineering#Stratosph...