I find this to be somewhat unlikely - it seems very strange to me that we could lose 40% of phytoplankton without there being disastrous effects fairly soon in terms of oxygen, sea life, etc. Conditionally, I'm calling this one sketchy and assuming something is not well understood here. That's not to say I don't think we've hashed it; just to say that I'm not sure we would be alive right now if we'd hashed it that bad. One thing I am certain of is that the Earth and life will outlast humans. There are a lot of things on this planet much more resilient than us naked apes. That's not much comfort, but I think it must be kept in mind when thinking about ecological disaster. Ultimately, we have to think in terms of our survival being dependent on maintaining an earth much like what has existed for the past 10,000 years. Sadly we're still stuck in the extraction mentality for the most part.