McCain got 0%. Turns out he failed to show up for any of the key environmental votes this year.
In at least one of the votes clearly key to the fight against global warming, he could have been the pivotal vote to change the outcome: "The provision to repeal billions of dollars in tax breaks for oil companies and put the funds toward clean, renewable energy fell one vote short of the 60 votes needed in the Senate." (LCV website)
In case you're wondering, Clinton and Obama both voted for that provision, and have scores of 73% and 67% respectively.
I guess McCain is just blowing hot air when he talks about his environmental principles.