Answer: No, mild carbonation of the oceans is beneficial to marine life.
The “evil twin” of global warming is said to be ocean acidification, endangering coral reefs and harming lobsters, crabs, oysters, and other shell-making creatures. It is allegedly causing “osteoporosis of the sea,” a term coined by Jane Lubchenko, Administrator of the National Oceanographic and Atmospheric Administration (NOAA) from 2009-2013. The oceans will be devastated “in a few decades,” predicts the 2009 Natural Resources Defense Council (NRDC) video Acid Test.
The ocean in fact is alkaline. A puddle of clean rainwater is 100 times as acidic.  Sea water has a natural local and regional variation in pH from 7.8 to 8.3 (neutral is 7.0). There is not enough carbon in all the currently usable carbon-containing fuels on earth to make the ocean acidic. Since the oceans contain 50 times as much CO2 as the atmosphere, adding all atmospheric CO2 to the ocean (in violation of Henry’s Law) would not make a measurable difference. Massive volcanic eruptions that resulted in ocean acidification some 252 million years ago released about 24,000 gigatons of carbon into the atmosphere, a total far exceeding today’s economically viable carbon-based fuel reserves of 3,000 GtC.
The figure below plots the effect of experimental pH reduction by adding CO2 or hydrochloric acid on calcification, metabolism, fertility, growth, and survival of various species.  A maximum decline of 0.09 to 0.17 in ocean pH by 2100 A.D. is a realistic projection of the effect of business-as-usual burning of carbon-containing fuels.  The UN Intergovernmental Panel on Climate Change (IPCC) makes a much more extreme prediction of a 0.3 to 0.5 pH unit. Results of all 1,103 studies of the effect of declines as great as a totally unrealistic 5.0 unit are available. 
Ocean carbonation also has the larger and more important effect of increasing photosynthesis. Thus, adding CO2 generally has a net positive effect on marine life. At least some shell-building animals (“calcifiers”) grow even faster than normal when transplanted to waters over natural volcanic CO2 vents. Photosynthesis can also raise the pH significantly.
Some experts predict that coral calcification will increase by about 35% beyond pre-industrial levels by 2100 because of rising seawater temperature. On the whole, the combination of rising temperatures and falling pH levels is beneficial, not harmful, to marine life, including corals. 
- Increasing the essential nutrient, CO2, enhances the growth of marine life.
- IPCC has exaggerated the potential maximal change in pH; moreover, life is resilient.
- Humans can stay warm, use coal-generated electricity, and drive gasoline and diesel-fueled vehicles without threatening to extinguish the life of shelled creatures in the oceans.
- Soon W. Acid Oceans, Osteoporosis of the Sea: the Failed Global Warming Scare. 28th Annual Meeting of Doctors for Disaster Preparedness. Orlando, FL; 2010. Available at: https://www.youtube.com/watch?v=6Xx2Jo12q0Q.
- CO2 Science. Ocean Acidification Data Base: Results and Conclusions. Available at: http://www.co2science.org/data/acidification/results.php.
- Tans P. An accounting of the observed increase in oceanic and atmospheric CO2 and an outlook for the future. Oceanography 2009;22:26-35.
4. Idso CD, et al. Climate Change Reconsidered II: Biological Impacts. Nongovernmental International Panel on Climate Change (NIPCC); 2014. Available at: https://www.heartland.org/_template-assets/documents/publications/full-report-ccr-ii-biological-impacts.pdf.
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