[bzxcvbn]

Good for you, but at least in the US, R600a (isobutane) is not used in AC units.

Besides, in the early XXth century, it was okay to vent CFC into the atmosphere. We didn't know that it destroyed the ozone layer. What makes you think that we won't discover something similar about isobutane in a few decades, besides wishful thinking?

[RL_Quine]

We study the greenhouse potential of gasses and have found r600a to have a potential of zero, in that it can not be ozone depleting.