Charlot, our Oceans campaign assistant, passed on this Power Point style presentation (in PDF format) by Jeremy Jackson. When it comes to credentials Dr. Jackson is no lightweight, and he does a great job of making things understandable. Lots of easy to interpret graphics.
Take a few minutes to flick through, and you'll have a good overview of the enormity of the crisis we're facing - or just skip ahead to slides 5 and 6, which speak volumes on their own.
A video version is available on the Harvard University website.
(And yes, I think Dr. Jackson has been giving this presentation for some years now, but I hadn't seen it before.)