Health of oceans in trouble

A BBC science report tells that the oceans may be in for a mass extinction. While the oceans have been absorbing CO2, they have been helping shield us from the effects of climate change. But as they absorb CO2, the ocean’s pH lowers.

Previous extinctions seem to have been caused by rising temperatures, lower pH, and less oxygen. With similar things happening now, how long until we reach a tipping point?