A study led by Sergei Petrovskii, Professor in Applied Mathematics from the University of Leicester's Department of Mathematics, has shown that an increase in the water temperature of the world's oceans of around six degrees Celsius -- which some scientists predict could occur as soon as 2100 -- could stop oxygen production by phytoplankton by disrupting the process of photosynthesis.
https://www.sciencedaily.com/releases/2015/12/151201094120.htm