Ocean acidification

The first assignment I give my students in Environmental Modeling class is to calculate the mass of the oceans versus the mass of the atmosphere and the “living” soil. They quickly determine that the oceans are by far the largest compartment on Earth, and so it is with some trepidation they realize humans are changing the content of something so incredibly immense. But, indeed, we are.

Ironically, the acidity emanates from a “weak acid” (carbon dioxide) injected into the global atmosphere at a rate of almost 50 billion metric tons per year. That is about 7 t for every man, woman, and child in the world! But it is not coming equally from every person—the U.S. still leads the planet (by far) in emissions per capita. Each time we fill our car with 10 gallons of gasoline, another 190 pounds of carbon dioxide is emitted into the air. The net effect: we take oxygen from the atmosphere and return loads of heat-trapping exhaust without ever having to pay a cent for the service. That is an externality. When the gases exchange with the oceans, they raise the dissolved carbon dioxide concentration and increase the acidity.

Still, the story seems incredible to my students, and I think the idea that we are acidifying the entire ocean is totally lost on the public. The oceans are well buffered, so it would seem they should resist acidification. With a high ionic strength of 0.7 M and a large alkalinity concentration of 2.3 mmol/kg, it is astonishing that the pH of the entire surface ocean has changed from about 8.2 to 8.08 in only 50 years or so. That may not sound like cause to worry, but it represents an increase in acidity (hydrogen ion concentration) of 30%! Such a change shakes the survival of coral reefs, diatoms, certain microcrustaceans, and zooplankton—the very base of the planetary food chain.

What’s more sobering is that the problem is getting rapidly worse. Global emissions continue to soar, while the buffer intensity of the ocean is declining. It follows from a massive disruption of natural geochemical cycles on earth. We are burning (oxidizing) carbon compounds which took millions of years to store in the earth’s crust, and releasing the gases to be stored in a relatively small atmosphere. It is out of balance, and the blow-down from so much oxidation is the inevitable surplus of the reaction products, carbon dioxide, and acidity.

I do not worry about “peak oil” wreaking havoc on prices and the economy. We have plenty of fossil fuels, and they are still priced far too cheaply. And do not let anyone tell you that we are running out of fossil fuels. We are not. Rather, we are running out of space in the atmosphere to store all our heat-trapping exhaust. I’m anxious for the date of “peak emissions” when humans will first level-off greenhouse gases and begin their requisite downward trajectory to a more sustainable climate and ocean chemistry. That will be a day for global celebration.

This editorial is a call for papers on “Ocean Acidfication: its Causes, Consequences, And Cures”. Our Managing Editor, Matt Hotze, and I will produce a special virtual issue, ES&T Select, on this crucial subject. We pledge to review your manuscripts promptly and publish the best ones in ASAP and ES&T with all the fanfare and publicity we can bring. We soon will be providing more information on “Ocean Acidification: Causes, Consequences and Cures”, an ES&T Select. Please check the journal homepage in the coming weeks for submission deadlines and instructions.

As a young chemical engineer in the early 1970s, I remember discussing the horrors of sulfur and particulate pollution from steel mills, smelters, and power plants. I remember Lake Erie “dying” and the Cuyahoga River catching fire. But I never would have believed that mankind could change the chemistry of the entire ocean so dramatically in my lifetime. It is not the same as a burning river, but it should cause concern about our future even more.

Schnoor J. L., 2013. Ocean acidification. Environmental Science and Technology 47(21):11919-11919. Article.


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