Except that Libertarian dogma holds that government regulations are detrimental to conservation, and that enlightened rational self-interest will prevent anybody from, for example, filling the air with carbon dioxide and pouring mercury into the rivers.

The Greens know that's a load of bullshit and requires totally ignoring all historical precedent, so any attempt to unite the two parties is doomed.

(Of course, that doesn't explain why, at least in the past, Greens advocated a maximum wage, taking businesses away from owners and giving them to the employees to run as collectives, a 100% tax bracket, etc.)