One Man Nearly Fried Us All

CFC, the refridgerant that is reponsible for holes in our ozone layer, and is now banned, was the discovery of one man. In 1930 fridges used toxic chemicals, and Thomas Midgely (who also put came up with the idea of putting lead in petrol) decided to find an alternative, non-toxic substance:

...Midgley began with the periodic table. A quick survey of known refrigerants showed that they all were compounds of hydrogen, carbon, nitrogen, oxygen, sulfur, and the halogens. Within this set of compounds, flammability decreased from left to right on the table, while toxicity decreased from bottom to top. The two trends pointed to fluorine as a promising candidate.
americanheritage.com

The rest is history, but it could have almost been every living thing on the planet that was history:

Indeed, back in 1930, Thomas Midgley might as easily have chosen bromine instead of chlorine as his active ingredient. Had he done so, the ozone hole would today cover the planet.

"More by luck than wisdom this catastrophic situation did not develop," said Nobel laureate, Paul Crutzen.
climatechange.ie