Acidification of our oceans: unprecedented rate in past 300 million years

Ahmed, Nafeez. 2017. Failing States, Collapsing Systems BioPhysical Triggers of Political Violence. Springer.

As climate change is accelerating, so is the acidification of the oceans. The two processes are causally related. Oceans are becoming more acidic because the vast bulk of global warming due to climate change is absorbed into the oceans, both in terms of the increase in temperatures, and in terms of actual carbon dioxide emissions. The massive increase in CO 2 levels in the oceans means that ocean pH levels are dropping dramatically. In a high emissions scenario—which characterizes our current business-as-usual trajectory—scientists cannot rule out further mass extinctions of marine life (Azevedo et al. 2015).

If this trend continues at current rates, before the end of the century, the scale of ocean acidification will threaten vast interconnected webs of marine life on which millions of people are dependent for their food supply and livelihoods. A major study in this regard notes that fully 80% of animal protein consumed in the world comes from fish. Yet at current rates, by 2100, an estimated 98 % of the oceans will be affected by a combination of deleterious climate impacts including acidification, low oxygen, and high temperatures. “These results highlight the high risk of degradation of marine ecosystems and associated human hardship expected in a future following current trends in anthropogenic greenhouse gas emissions,” conclude the study authors (Mora et al. 2013b).

Ocean acidification has also been discovered to be a prime driver of the largest mass extinction event in the history of the planet, the Permian-Triassic extinction event. The rate at which carbon was released during that event is similar to the rate of modern carbon emissions (Clarkson et al. 2015).

Hönisch, Bärbel, et al. 2 Mar 2012. The Geological Record of Ocean Acidification. Science vol 335 #6072 1058-63.

This paper looks at the last 300 million years of acidification of oceans (beyond that it’s hard to find evidence) and concludes that the rate we’re acidifying the ocean is unprecedented, which makes it hard to predict the outcome.

Extinctions in the past were caused by both warming and consequent oxygen depletion as well as acidification from volcanic eruptions.   Our burning of fossil fuels is causing a faster release of CO2 than past volcanic eruptions– faster than any of the 5 mass extinctions in the past, so we can’t predict how soon and what magnitude the next extinction will be.  But it may be of a magnitude unparalleled by any extinction in the past.  The Permian extinction killed up to 95% of ocean life.

References

Azevedo, Ligia B., An M. De Schryver, A. Jan Hendriks, and Mark A.J. Huijbregts. 2015. Calcifying Species Sensitivity Distributions for Ocean Acidification. Environmental Science & Technology 49(3): 1495–1500.

Clarkson, M.O., S.A. Kasemann, R.A. Wood, T.M. Lenton, S.J. Daines, S. Richoz, F. Ohnemueller, A. Meixner, S.W. Poulton, and E.T. Tipper. 2015. Ocean Acidification and the Permo-Triassic Mass Extinction. Science 348(6231): 229–232.

Mora, Camilo, , et al. 2013b. Biotic and Human Vulnerability to Projected Changes in Ocean Biogeochemistry over the 21st Century. PLOS Biol 11(10): e1001682.

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