I feel like any such discussion must address the fact that, globally, phytoplankton has declined by 40% in the past century. That's 40% of the base of the food pyramid for all ocean life. That's 20% of the plant life in the world, and accounts for 20% of the oxygen we breathe. Whatever is causing it, something significant is happening to the ecosystems of earth.

http://wormlab.biology.dal.ca/ramweb/papers-total/Boyce_etal...