When I took my first graduate level physical chemistry class many years ago, I had a professor who spent several lectures demonstrating how the human emission of carbon dioxide through the burning of fossil fuel could not contribute to the accumulation of greenhouse gases in the atmosphere and cause atmospheric temperatures to rise. His chemical equations showed how ocean water reacts with carbon dioxide in the atmosphere and essentially removes it. The chemical equations for this exchange are actually very simple and quite well known. Carbon dioxide, which is CO2 (carbon and oxygen), reacts with water, which we know is H2O (hydrogen and oxygen), to form carbonic acid (H2CO3). Carbonic acid then further reacts with ocean water to produce bicarbonate (HCO3) and free hydrogen ions.
You’re thinking, we’re saved! We don’t have to worry about those carbon dioxide emissions from power plants and cars anymore. Let’s pump more oil and gas out of the ground and to heck with driving a Prius. Where’s my Hummer?
Well not so fast. My physical chemistry professor forgot to explain to us what happens to the ocean after this chemical exchange. What do we remember about free hydrogen ions? They are a measure of acidity. Remember pH? It is a scale of measurement from 1 to 14 where 7 is neutral. Anything below 7 is acidic and anything above 7 is basic. The pH of a solution is simply a measure of free hydrogen ions. The more free hydrogen you have, the more acidic your solution. So when the ocean reacts with carbon dioxide from the atmosphere, it is becoming more acidic. This is what is known as ocean acidification.
The pH of the oceans range from 7.8 to 8.4. So right now seawater is mildly on the basic side. The pH of the oceans is something scientists have been measuring for a long time. The change in the pH of the ocean can also be calculated based on man’s carbon dioxide emissions. Scientists have made an inventory of greenhouse gas emissions dating as far back as the start of the industrial age. Such inventories are not your most accurate of measures, especially when you are looking at emissions from several hundred years ago, but if anything they are probably undercounting emissions. The International Panel on Climate Change in their 2013 Report “The Physical Science Basis” states that currently the amount of total carbon dioxide from human emissions being stored in the ocean is 30 %. According to calculations using such inventories there has been a 0.08 decrease in pH in the ocean’s surface water between 1765 and 1994.
Direct measurement of pH taken since 1991 in the North Atlantic and North Pacific have shown a steady decrease ranging between ‾0.0014 and ‾0.0024 per year. These numbers reflect regional variations in pH decreases. The IPCC report states the variability in the decline of pH is a reflection of high latitude oceans not as effectively absorbing carbon dioxide.
The pH decreases seem tiny don’t they? But think about this. Oceans cover almost three-fourths of our planet; that is a lot of water. The fact that carbon dioxide emissions can change the pH of the entire surface water of the ocean every year by even these tiny amounts is phenomenal. Say you took the mid-range of this yearly decrease (‾0.0019) and multiply it by 1000 years. You would be looking at almost a pH decrease of 2 by the year 3016. You would be going from slightly basic ocean water to slightly acidic ocean water, just from human carbon dioxide emissions.
On the short term there are a lot of scientific researchers who are studying the impacts that these slight yearly decreases may be causing. None other than the National Academy of Sciences has weighed into the impacts of ocean acidification by developing “A National Strategy to Meet the Challenges of a Changing Ocean (2010).” Ocean Acidification is a big concern of scientists, after all humans are changing the very chemistry of the earth’s oceans.