CO2-Caused Ocean Acidification – Causes and Consequences

“The CO₂ problem” has traditionally been understood as the fact that excessive CO₂ produces global warming. But near the end of the 20th century, scientists started talking about a second CO₂ problem, “ocean acidification”. Ocean acidification results from the fact that about 30 percent of our CO₂ emissions have been absorbed by the ocean. This absorption keeps down the warming of the atmosphere that would otherwise be produced by these emissions. Ocean acidification involves the ocean’s pH, changes in which make the water become either more alkaline or more acidic.

Tests have shown that “for more than 600,000 years the ocean had a pH of approximately 8.2.” But since the industrial revolution, the ocean’s pH has dropped by 0.1 unit. That may not sound like much, “but pH is a logarithmic scale, so the decline in fact represents a whopping 30 percent increase in acidity.” Moreover, the IPCC has said that if business as usual continues, the pH may drop down to 7.8, which “would correspond to a 150 percent increase in acidity since pre-industrial times.”

Why is acidification destructive?

When carbon dioxide is combined with water, it produces carbonic acid – which is the ingredient that, besides giving soft drinks their fizz, also eats out limestone caves. Its relevance here is that it does this to animals with chalky skeletons – that is, ones that calcify – “which make up more than a third of the planet’s marine life.” Elevating the percentage of carbonic acid will make it increasingly difficult for calcifying organisms to make their skeletons – organisms such as plankton, corals, sea butterflies, molluscs, crabs, clams, mussels, oysters, and snails.

Most of us are, of course, especially interested in the ones we like to eat. More important for the cycle of life, however, are two tiny organisms, corals and plankton, which are at the base of the marine food web.

Phytoplankton

There are two basic types of plankton: phytoplankton, which are microscopic plants, and zooplankton, which are microscopic animals. The most basic type is phytoplankton, because they are capable of photosynthesis and are thereby the food for zooplankton (which in turn provide food for bigger animals). Besides providing about half of the biosphere’s oxygen, phytoplankton also account for about half of the total organic matter on Earth, so they provide “the basic currency for everything going on in the ocean.” We do not, of course, feast directly on phytoplankton, but they “ultimately support all of our fishes.”

Therefore, a reduction in the ocean’s phytoplankton is extremely serious: A major study in 2010 has already indicated that there has been an astounding reduction: 40 percent since the 1950s. “A 40 percent decline,” said Worm (one of the study’s coauthors), “would represent a massive change to the global biosphere.” Indeed, he said, he could not think of a biological change that would be bigger. Referring to this 2010 study, Joe Romm said: “Scientists may have found the most devastating impact yet of human-caused global warming.” Explaining the importance of the study, its lead author, Daniel Boyce, said that “a decline of phytoplankton affects everything up the food chain.”

In 2013, additional studies suggested that phytoplankton are very sensitive to warmer water. In one study, scientists at the National Oceanic and Atmospheric Administration reported on the normal spring surge of phytoplankton, which provides food for various types of fish when they are producing offspring. In the spring of 2013, the North Atlantic’s water temperatures were “among the warmest on record” and the springtime plankton blooms of northern New England were well below normal, “leading to the lowest levels ever seen for the tiny organisms.”

Corals

Corals form coral reefs, which have been called the “rainforests of the sea,” because they play host to much of the oceans’ life. Already threatened by bleaching, which is caused by global warming, they are now further threatened by global warming’s evil twin. Corals form their skeletons by means of calcium carbonate in the sea water. As the water becomes more acidic, it is harder for the corals to calcify. In the past 30 years, calcification rates of corals on the Great Barrier Reef have declined by 40 percent. “There’s not much debate,” said Professor Ove Hoegh-Guldberg of the University of Queensland, “about how [the decline] happens: put more CO₂ into the air above and it dissolves into the oceans.“

This decline has not only occurred off Australia. A 2013 study of coral reefs in the Caribbean found that many of them “have either stopped growing or are on the threshold of starting to erode,” due to difficulty in accumulating sufficient calcium carbonate. The amount of new carbonate being added to the reefs was found to be far below historical rates, in some cases 70 percent lower.

And yet the accumulation of carbonate is necessary for the reef to grow vertically, which is essential, given the rising sea level; coral reefs need to be close enough to the surface for sunlight to reach them. The leader of the study said: “Our estimates of current rates of reef growth in the Caribbean are extremely alarming.”

A World without Seafood

Acidification, which threatens both phytoplankton and corals, has speeded up. Professor Timothy Wootten of the University of Chicago reported in 2008 that the pH level was “going down 10 to 20 times faster than the previous models predicted.” The more it goes down, the more difficult it will be for organisms such as corals and phytoplankton to calcify. CO2 in the atmosphere is now at about 400 parts per million. If it reaches roughly 500 ppm, according to Ove Hoegh-Guldberg, “you put calcification out of business in the oceans.”

If and when this occurs, phytoplankton and corals will die, and their death will mean that crabs, clams, oysters, and scallops will disappear. And they are already disappearing, faster every year. In the Pacific Northwest and British Columbia, the waters have become so acidic that the once-thriving shellfish industry there is on life support.” In 2014, scallop growers in a location near Vancouver, B.C., reported that 10 million scallops over the past two years had died, with the mortality rate hitting between 95 to 100 percent.

The disappearance of the phytoplankton will also lead to the death of sardines, which are just above them in the food chain. And “the sardine population from California to Canada is vanishing,” resulting in starving sea lion and seal pups, and brown pelicans are showing signs of starvation, not raising any chicks in the past four years. Eventually, the disappearance of phytoplankton and corals will mean that all fish will go, as emphasized by a film subtitled Imagine a World without Fish. “Continued rise in the acidity of the oceans,” the script forewarns, “will cause most of the world’s fisheries to experience a total bottom-up collapse.”

A world without fish and other kinds of seafood is hard to imagine. It would be even harder for the planet’s people to live without seafood: Besides being the world’s largest source of protein, with over 2.6 billion people depending on it as their primary source of protein, the ocean also serves as the primary source of food for 3.5 billion people.

How would we survive if three and a half-billion people can no longer rely upon what has always been their primary source of food? “Global warming is incredibly serious,” said Hoegh-Guldberg, “but ocean acidification could be even more so.”

Conclusion

Nevertheless, although the world’s governments have been warned about acidification for many years, already in 2010 the oceans were “acidifying 10 times faster today than 55 million years ago when a mass extinction of marine species occurred.” CO₂-caused climate changes have already made the planet’s food shortage worse. Over the next three decades, climate changes will make it still worse. These shortages will be further exacerbated by the reduction of seafood because of CO₂-caused ocean acidification.

Note: This excerpt has been published from Prof. David Griffin’s book Unprecedented: Can Civilization Survive the CO₂ Crisis which is available at this link.