I’m afraid the term "Republican environmentalist" has become an oxymoron. For example, John McCain has reasonable environmental credentials. However, he is also the head of the Bush re-election campaign in Arizona. If McCain contributes to a Bush victory in Arizona, and hence nationally, this will negate any positive contribution to the environment that McCain may have made as senator.
This isn’t your daddy’s Republican party, either, and environmentalists shouldn’t support it. Economic libertarians and religious fundamentalists have taken over the GOP. Their agenda is a cornucopia of astoundingly inconsistent positions, but doesn’t include any meaningful protection for the environment.