As executive secretary of the Convention on Biological Diversity Ahmed Djoghlaf recently observed, "Climate change has become one of the greatest drivers of biodiversity loss." Indeed, the latest assessment by the UN's Intergovernmental Panel on Climate Change concluded that 20 to 30 percent of species would likely face an increased risk of extinction if globally averaged temperatures rise 1.5-2.5ºC above 1980-1999 levels, and that 40 to 70 percent of species could be rendered extinct should temperature increases exceed 3.5ºC, a temperature scenario that is becoming increasingly possible by the end of this century. A large portion of the species that are imperiled inhabit the world's oceans, including fish, marine mammals, corals reef ecosystems, and plankton.
The vast majority of oceanic climate research in recent years has focused on the potential impacts of increasing temperatures on ocean ecosystems as a consequence of rising levels of anthropogenically-generated carbon dioxide and other greenhouse gases, including methane, nitrous oxide, and chloroflourocarbons. However, there is growing evidence that the gravest peril for ocean species may be posed by what Victoria Fabry of the Pacific Marine Environmental Laboratory has termed "the other CO2 problem"-acidification of the world's oceans as a consequence of the influx of carbon dioxide generated by human activities.
This article assesses the threat posed by ocean acidification during this century and beyond. It outlines the science associated with ocean acidification, assesses the likely impacts of ocean acidification on species and ecosystems over a horizon of the next 300 years, and lays out an agenda for future research.