What is Ocean Acidification?
Since the beginning of the industrial revolution, human activities have accelerated the release of carbon dioxide (CO2) into the atmosphere. Scientists estimate that the carbon dioxide in the air has increased 30% over the last 200 years, from approximately 280 parts per million to 385 ppm. This means that the concentration of atmospheric carbon dioxide is now higher than it’s been on Earth for almost a million years. Just as significant, the speed at which this CO2 is increasing is faster than anything experienced before. Based on mankind’s current use of fossil fuels, the amount of carbon dioxide in the atmosphere is only expected to increase, and scientists are becoming concerned that this increase will cause significant changes to our climate and to life on Earth in the coming decades.
During this time the oceans have been absorbing approximately 30% of the carbon dioxide we’ve released. This absorption has reduced the amount of CO2 in the air and probably minimized some of the terrestrial impacts of climate change such as global warming. However, carbon dioxide does not just disappear once it enters the water; it significantly affects the chemistry of the seawater itself. One of the biggest effects it causes is a change in the seawater’s pH. As carbon dioxide mixes with water, the two molecules combine to become carbonic acid which makes the seawater slightly more acidic. As billions of molecules combine and go through this process, the overall pH of the oceans begins to change. This phenomenon is called “ocean acidification”.
In the last century, the pH of ocean surface waters has already decreased from an average pH of 8.2 to 8.1. Even slightly lowering the pH of the seawater can be hard on marine organisms and affect processes such as growth, metabolism and reproduction. A reduction in ocean pH also reduces the availability of carbonate ions in the water, which are important for shell formation in many marine organisms. Animals like corals, snails, urchins, and shellfish pull carbonate out of the water to calcify their hard parts; thus, as the concentration of those materials decreases in acidified water it gets harder to create a shell. For some organisms, carbonate structures can even start dissolving when the water chemistry becomes too unfavorable.
The Intergovernmental Panel on Climate Change (or IPCC) has predicted that atmospheric CO2 levels will continue to go up over the next century - from today’s already elevated level of 385 parts per million to perhaps as high as 1000 parts per million by the year 2100. Scientists are rapidly developing research programs to study what these predictions mean for marine organisms, ecosystems and biogeochemical cycles. Currently, little is known about what this increase of CO2 will do to life in the oceans. But the knowledge that these climate changes are happening raises grave concerns with policy makers, scientists, and citizens worldwide.