Climate change has been talked about for decades now, and very little actually seem to be done. What is something you would consider a number 1 that was fixed? (I guess the ozone layer hole was a relative success).
On the drawdown website, refrigeration seems to be #1. Afforestation is up there. Family planning too. But supposedly we have to be doing all of these things on massive scale.
I was considering saying "nothing ever gets fixed" and toned it down to what I wrote specifically because I remembered CFCs.