I think people would have figured out a way to make sustainability ridiculously profitable a lot earlier in the game. And then they would have spent the money on coke and ridiculously expensive krill-based nouvelle cuisine. Imagine a cross between "The Greening Of America" and "American Psycho" and you're getting the picture.
Seriously, though: I've always believed that environmentalism has been crippled by all the weird bullshit attached to it. Sustainability and Native American rights have fuck-all to do with one another, for example, but you would have gotten lynched if you'd suggested that to hippies in the 70s. (I'm not minimizing Native American rights, of course, but you take my point.) Environmentalism has traditionally been handcuffed to the most ridiculous aspects of post-60s Leftism.
We've been changing that in this new century, thanks in large part to people like you and Big Bruce Sterling (and, to a much lesser extent, um, me). But if Carter had been elected? Was the hyper-capitalism of the 80s connected entirely to Reaganism? I like to think my first statement would have been the case. There's a lot of money to be made in cleaning up the environment, and the best part -- if you'll forgive my cynicism -- is that much of it comes from fat government contracts.
I think you would have seen a weirder form of socialist-capitalism emerge. And I do think that we'd be a good deal less consumerist as a society.
And the fiction writer in me deeply digs on the image of an alternate Gordon Gecko, in an Armani suit woven from renewable bamboo fiber and Nia Peeples yuppie glasses made from recycled pressed sunflower seeds, moving billions of dollars between coal-pollution suppression firms and multinational reforesting conglomerates.
Green is good. Green is right. Green works.