IF you could fix the environment completely, what would be the first step?
Exclude advocacy and education, this hypothetical is that everyone's already on board.
My first step: Focus on the ocean because it creates more of our oxygen than anything else.
Step1: Further regulate shipping lanes making sure they come no where near coral reefs.
Step 2: Set up foundations where college kids to earn credits for classes or for their doctorates degree they get trained to scuba dive, where after they will be tasked with defending ocean kelp fields from an over populations of sea urchins.
I would join in on your idea. Starting with the Ocean would be the best start. I would after those first two steps,
Step 3: Have organizations about the world monitor chemical levels in their own oceans to see where the highest concentrations of certain chemicals are coming from
Step 4: Taper down on Ocean fish for food like Tuna, Sharks, and Whales. Of course that would impact tens of thousands of jobs so we would first try to train and hire them in projects that we created to protect the ocean first so we didn't put people out of work.