One frequently neglected consequence of rising global concentrations of carbon dioxide is increasingly acidic oceans (though it has been mentioned here before). Since the Industrial Revolution, the world ocean has absorbed about 118 billion tons of anthropogenic CO2: half of total human emissions. Every day, another 20-25 million tonnes are being absorbed.
Before the Industrial Revolution, oceanic pH was about 8.179. Now, it is at 8.104. By 2100, it is projected to be 7.824. Because pH is a logarithmic scale, that is a bigger change than it seems to be. At the projected 2100 concentration, the shells and skeletons of corals, molluscs, and phytoplankton with aragonite shells begin to dissolve within 48 hours. James Orr et al, writing in Nature provide many more details:
In our projections, Southern Ocean surface waters will begin to become undersaturated with respect to aragonite, a metastable form of calcium carbonate, by the year 2050. By 2100, this undersaturation could extend throughout the entire Southern Ocean and into the subarctic Pacific Ocean. When live pteropods were exposed to our predicted level of undersaturation during a two-day shipboard experiment, their aragonite shells showed notable dissolution. Our findings indicate that conditions detrimental to high-latitude ecosystems could develop within decades, not centuries as suggested previously.
The effect of more acidic oceans on aragonite is part of why the Stern Review projects that coral reef ecosystems will be “extensively and eventually irreversibly damaged” at less than 450 ppm CO2 equivalent and less than 2Â°C of warming. Given how critical coral reefs are to overall oceanic ecosystems – including key commercial fish species – this should be of concern to everyone.
It is very hard to project what the consequences of all this will be. As with so many other climatic phenomena, the net impact for human beings probably has to do with the relative strength of positive and negative feedbacks and the corresponding resilience of ecosystems. What is certain is that the only way to prevent acidification is to signficantly cut CO2 emissions.