There’s always room for one more post about oceanic acidification. Even Sheril Kirshenbaum understates the threat that it poses to the planet’s ecosystems and civilization when she describes it a “huge deal.” First, let’s get one thing straight:
Falling pH levels in the seas do not constitute global warming’s “evil twin.” That would imply that global warming is oceanic acidification is global warming’s good twin. Both are evil. The malapropism was used in a paper published earlier this year in Trends in Ecology & Evolution by a trio of researchers from Spain and Australia, but it’s been around a lot longer than that, and should be put to rest immediately.
That paper, Paleo-perspectives on ocean acidification, is however, a good introduction to the subject. Here’s the abstract, which boils it all down to the essentials (emphasis mine):
The anthropogenic rise in atmospheric CO2 is driving fundamental and unprecedented changes in the chemistry of the oceans. This has led to changes in the physiology of a wide variety of marine organisms and, consequently, the ecology of the ocean. This review explores recent advances in our understanding of ocean acidification with a particular emphasis on past changes to ocean chemistry and what they can tell us about present and future changes. We argue that ocean conditions are already more extreme than those experienced by marine organisms and ecosystems for millions of years, emphasising the urgent need to adopt policies that drastically reduce CO2 emissions.
Why is it a problem? Because many of the tiny critters at the base of the marine food web — the one on which a couple of billion people rely for their protein — have evolved to thrive in a narrow window of pH values. Yes, they can adapt to changes, and pH values have risen and fallen by significant amounts over the eons, just not nearly as fast as they’re changing now. Some organisms build their shells from molecules that won’t be available if pH levels fall too much. That much is well known. But there are many other impacts.
For example, as a recent paper in PNAS points out, Others won’t be able to smell their way around their environment, and these “olfactory cues” are essential for some species if they want to successfully breed:
…elevated CO2 and reduced seawater pH that could occur early next century in the world’s oceans can dramatically affect the behavioral decisions of marine organisms during critical stages of their life-history.
That research involved rearing clownfish in relatively acidic water, an environment with a pH level of 7.60 or 7.80. Today the average oceanic pH is about 8.07, which is about 0.1 lower than pre-industrial levels, but a new paper in Geophysical Research Letters,”Influence of mitigation policy on ocean acidification,” by a trio of British researchers estimates the expected future pH by the end of the century will be as low as 7.67.
Looking closer at the mitigation-effects paper show just how serious things are. The authors conclude that even if we find a way to get off the fossil-fuel train, emissions peak by 2016 and fall by 5% a year thereafter (a scenario most would call wildly optimistic), oceanic pH would still fall to 8.02, which represents “slightly less than a doubling of the change in pH since the pre‐industrial era.”
If, however, we do nothing (the IPCC’s “A1FI” scenario) or only a little (A1B) the effects would be even more dire.
We find that an A1FI scenario would further decrease pH to 7.67 [7.74-7.57] by 2100 (where the square brackets indicate the 10th and 90th percentile values). For A1B pH would reach 7.81 [7.86- 7.71]. These pH minima during the next century are 3.9 to 5.4 times the current change in ocean pH since 1750 and are likely without precedent in the last 21 million years [Pearson and Palmer, 2000], a period over which many
oceanic organisms have evolved to survive in a narrow range of pH.
It’s also worth pointing out (for the umpteenth time) that most geoengineering schemes involve only technologies designed to counter the effects of fossil-fuel emissions, not reduce actual emissions. Around half the CO2 we emit ends up in the oceans, so the oceans would continue to experience falling pH levels. Add that to the list of consequences that geoengineering would not mitigate.
Bernie, D., Lowe, J., Tyrrell, T., & Legge, O. (2010). Influence of mitigation policy on ocean acidification Geophysical Research Letters, 37 (15) DOI: 10.1029/2010GL043181