PLANETARY LIMIT #4 OCEAN ACIDIFICATION: 3 THINGS YOU NEED TO KNOW ABOUT CO2 EMISSIONS AND OUR OCEANS
By Jane Fiona Cumming
1. What is ocean acidification?
Increasing CO2 in the atmosphere due to human activities not only affects the climate; it also has direct, chemical effects on ocean waters with the formation of carbonic acid increasing the acidity (lower pH) of the surface seawater. In the past 250 years’ ocean pH has decreased by about 30%. If we continue emitting CO2 at the same rate, by 2100 ocean acidity will increase by about 150%. 
2. What are the effects of ocean acidification?
Currently oceans absorb ~25% of human CO2 emissions, ocean acidification reduces the capacity of oceans to do this.
Ocean acidification poses a challenge to marine biodiversity. It results in the loss of calcifying marine organisms with serious impacts on the productivity of coral reefs and ripple effects up the food chain. Phytoplankton are the foremost link in the food chain, supporting simple marine life, right up to the blue whale. 
Through photosynthesis, phytoplankton absorb carbon dioxide to produce nearly 50% of the oxygen we breathe, thereby playing a fundamental part in our battle against climate change. But phytoplankton are however under threat. In parts of the oceans, populations of these microscopic organisms are plummeting. This decline is related to increasing sea surface temperatures and ocean acidification (the pH of the oceans has shifted to 8.1 from 8.2 and could drop to 7.8 by the year 2100). 
3. What can corporates do?
Ocean acidification is a massive threat to plankton, and therefore marine animals and ultimately the Earth itself. Over the past 5 years as we have tracked how the world’s largest companies are measuring their impacts on Planetary Limits only one company has reported measuring activity relating to ocean acidification, so this must be considered within the wider scope of climate change efforts.
In 2019, 79% of the companies reported emissions associated with their wider value-chain (scope 3) emissions, which combined represented 10.7bn tonnes CO2e, over five times the amount of their Scope 1 and 2 emissions. Crucially, only 21% of companies had set targets to reduce their scope 3 emissions although they account for an enormous carbon footprint in comparison to scope 1 and 2 emissions.
For the corporate sector to play its part in the achievement of global climate change targets it must address its real impact on the planet’s resources and base reduction targets on what the world needs them to do.
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 Ocean Acidification Programme 2016. See more at: http://www.whoi.edu/ocean-acidification/#sthash.x7UVklCr.dpuf
 Gattuso et al 2014