Scientists have known for decades that when carbon dioxide mixes with ocean water it creates an acid, but only recently did they begin to realize what this growing quantity of acid would mean for ocean life. As you can see in the film, this new understanding has some of the world's leading ocean scientists quite freaked out.
What they can say with assurance is that if we continue burning fossil fuels as we are now, we will double the ocean's natural acidity by the end of the century. What's less clear is how damaging that will be for ocean life.
Scientists believe many organisms may not survive so radical a shift in chemistry. And some of those organisms -- plankton and corals, for instance -- form the foundation of the ocean food web.
If they perish, what happens to the hundreds of thousands of species further up the chain?
Scientists just don't know. But their fear is summed up in the film by Dr. Ken Caldeira of the Carnegie Institution: "We're moving from a world of rich biological diversity, essentially into a world of weeds."