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Lessons From History on Ocean Acidification

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Part of my job involves fielding worried emails and phone calls about alarming-sounding science news, especially when it relates to ocean acidification. Recently a study in Science made a big splash, generating headlines like “Ocean acidification caused the largest mass extinction ever” and “Acidic oceans helped fuel extinction.” And those are some of the calmer headlines. Naturally, people are saying, “This is scary stuff! Are we going to see the same thing?” Let’s take a look.

When studying major global changes like warming, ocean acidification, or ocean oxygen loss, scientists often look back in the geological record to see what happened when Earth experienced similar conditions before. That helps scientists put global change in the proper perspective.

In past geological ages when volcanic activity has been high, atmospheric carbon dioxide levels have risen and dramatically changed the Earth’s climate and ocean chemistry. Last week’s Science study focuses on one of these periods—the Permo-Triassic (P-T) boundary. It’s one of the most “rapid” releases of volcanic carbon dioxide to the atmosphere, taking 60,000 years. As slow as that seems, it’s fast for the Earth—60,000 years out of a 4.5 billion year old planet’s life is like half a day of a 100-year-old person’s life. All this volcanic carbon dioxide drove rapid ocean acidification towards the end of the P-T boundary, and a major extinction of ocean life followed. Marine life with calcified shells and skeletons, like corals, shellfish and calcifying algae, were pretty much wiped out.

This science study offers insight into what extreme, unchecked ocean acidification could look like. The rate of carbon dioxide release to the atmosphere that drove acidification during the P-T boundary was about the same as today’s. However, the P-T boundary isn’t exactly like today. The total amount of carbon released then was nearly five times as large as ALL the fossil fuel reserves on Earth. Also, ocean pH dropped by up to 0.7 pH units during the P-T boundary, but ocean pH has only decreased today by 0.1 units, with another 0.2-0.3 units expected by 2100. Most scientists agree we probably won’t see wholesale extinction of shelled animals and corals from today’s ocean acidification. But if we even just put a dent in marine populations over mere moments of the Earth’s life, that’s pretty scary. To the Earth, the 200 years we’ve been emitting carbon dioxide is like two minutes of a 100-year-old’s life.  We’ve made huge changes to the ocean in a small amount of time.

What are our options? To avoid repeating geological history, mankind needs to cut carbon dioxide emissions swiftly and decisively. Nations are pledging to do this in preparation for this year’s United Nations Conference of the Parties (COP 21) meeting. Researchers are exploring how to do this in ways that will lead to overall socioeconomic benefits in the short and long terms. Some programs, like the long-running U.S. Energy Star program, have already shown that citizens can benefit financially while saving energy. Meanwhile, local and regional governments are seeking ways to cut their own carbon dioxide emissions. Maine and Maryland have recently called for reductions in carbon emissions as one of several steps they’ll take to combat ocean acidification, echoing Washington State’s resolve. West Coast states and British Columbia are working on this collaboratively. At the same time, businesspeople are finding ways to adapt to, or stave off, some of the worst effects of ocean acidification. But since humans depend on marine life of all types, calcified or not, protecting creatures in the ocean is actually in our own self-interest. Formally committing to cut our carbon dioxide emissions, which every country can do at this year’s COP 21 meeting, is a big but needed next step to protect the oceans and ourselves.

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