Image courtesy of NASA. Someone sent me these NASA images. The top one shows change in surface temperature. The bottom, change in phytoplankton productivity. Overall, warmer surface temperatures meant less productive phytoplankton. True, towards the poles there will probably be some increase in productivity, but the overall effect is negative.
Why should we care? From the NASA website:
Every day, more than 100 million tons of carbon dioxide are drawn from the atmosphere into the ocean by billions of microscopic ocean plants called phytoplankton during photosynthesis. In addition to playing a big role in removing greenhouses gases from the atmosphere, phytoplankton are the foundation of the ocean food chain.
“Rising levels of carbon dioxide in the atmosphere play a big part in global warming,” said lead author Michael Behrenfeld of Oregon State University, Corvallis. “This study shows that as the climate warms, phytoplankton growth rates go down and along with them the amount of carbon dioxide these ocean plants consume. That allows carbon dioxide to accumulate more rapidly in the atmosphere, which would produce more warming.”
That is to say: more CO2 = warmer oceans = less productive phytoplankton = more CO2 and less food for marine life.