Over the last ~200 years, since the start of the industrial revolution, the increase in the burning of fossil fuels, cement manufacturing and changes to land use has increased atmospheric CO2 concentrations from ~280 to 385 ppm. These are the highest levels experienced on Earth for at least the last 800,000 years, possibly for the past 10’s of millions of years. The 2007 IPCC report on climate change predicts a continued rapid rise in atmospheric CO2 leading to significant temperature increases in the atmosphere and ocean in the coming decades, as well as other climate changes. The IPCC (2007) also reports, for the first time, that increasing anthropogenic CO2 will result in increased acidity of the world’s surface oceans. This process is already happening and further rapid decreases in ocean pH will occur this century, concomitantly with warming seas, creating multiple threats to the marine environment. The future addition of massive amounts of CO2 to surface waters will have a profound impact on ocean chemistry and could have an equally profound impact on biogeochemical cycles, marine organisms, ecosystems and the services they provide. ‘Ocean acidification’ is a strong additional argument to that of climate change for urgent and substantial reduction of CO2 emissions.