Sure there's about 6 billion people in the world but a lot of them don't go in the water. Of those that do go in, all don't wear sunscreen, and all aren't going in the water around coral reefs. Coral is pretty sensitive and can be damaged/killed by numerous things some of which can be attributed to human activity but I'm still not sold on sunscreen. There's about 330,000,000 cubic miles of ocean and I just don't see how sunscreen could be a factor. I could see how global warming, sediment, harbors, hotels, urbinization, boats....etc can kill the reefs. There are just too many factors that have to be accounted for to conclude sunscreen.