Well if it's going to take several trillion dollars to deal with effects of climate change, then however much money we thought we had saved by going with fossil fuels over cleaner but more expensive energy sources was actually overstated by several trillion dollars. I don't think that covers all economic growth though. And if a manufacturer pollutes the crap out of a river and gets people sick, I would deduct the costs borne by the people downstream from the profits of the company, at least when counting "economic growth". I suspect in terms of GDP it's a positive, because of the business created for doctors and lawyers.