It’s not precisely global. Throughout the world it correlates best by far with the year that a given country, state, or region phased out leaded gasoline. I.e.

It’s not precisely global. Throughout the world it correlates best by far with the year that a given country, state, or region phased out leaded gasoline. I.e. declines did not start in same year in every country. They almost entirely began 18-30 years after phase-out of leaded gasoline.