. . . the answer is man-made global warming.
Read this article and weep for the man's lack of scientific integrity and even intellectual coherence.
One of the cornerstones of the catastrophist scam is that global warming decreases the oceans' ability to absorb carbon dioxide.
Furthermore, warm waters encourage the growth of coral reefs, which is why they are concentrated in the tropics. Lastly, algae love soupy water.
So, Dr Jacob Silverman of the Carnegie Institute in Washington, why don't you just go away and play with yourself in private?