When Cuba lost their fossil fuel pipeline when the Soviet Union collapsed in 1990. Overnight they had no choice, they had to transition to clean energy, they didn't have any fuel to burn, and they also had to transition to a healthy food system, an organic system - their economy is crashing, this was not a planned transition. This was a crisis, but a crisis nonetheless, in which pollution went away. And it's very instructive to see what happened to their health.
