Ocean Acidification – The Other CO2 Problem

By Jim Thrall

The public is generally aware of climate change, or, as it is more commonly known, global warming. Despite the efforts of the climate deniers, largely funded by the oil, gas, coal and auto lobbies, rational and informed members of the public understand that the major cause of climate change is our continual addition of carbon dioxide (CO2) to the atmosphere, through the use of fossil fuels to power our industrial society. As discussed below this increase in CO2 has two separate effects on the earth that we should be concerned about. One is climate change the other is acidification of the ocean.
The cause of these two phenomena is relatively simple to understand. Carbon is one of the essential elements of life that our planet recycles between the biosphere, the atmosphere, and the ocean. Over millennia, large amounts of carbon were put into long term storage in the form of coal, oil, gas and limestone. However, in just the last 150 years or so, our use of coal, oil and gas to power industrial society has released massive amounts of this stored carbon into the atmosphere in the form of CO2. The rate of release is such that the atmospheric concentration of CO2, which fluctuated between 180 to 300 parts per million (ppm) over the last 800 thousand years, has risen, in what is the geological equivalent of the blink of an eye, to today’s level of just under 400 ppm. If an increase of 100 ppm seems a small number, keep in mind that this is the concentration in the entire atmosphere. In 2008 the total world emissions of CO2 due to human activity was almost 30 billion metric tons. Because the natural cycling of carbon due to photosynthesis and respiration involves the annual movement of nearly 800 billion tons of CO2 per year this again may seem like a small amount. However, this addition of a “small additional amount” into the carbon cycle occurs each and every year. And, there are only two places this excess CO2 can go, the atmosphere or the oceans. Thus we see the rapid and constant rise in atmospheric CO2. This increase would be even greater had the oceans not absorbed a significant portion of the excess. In fact, the oceans have absorbed about one half of all the CO2 released by human activities. Currently the oceans are absorbing about 30 million tons of CO2 per day. This has reduced the rate of global warming somewhat, but only at the expense of acidifying the sea. So we have two effects to be concerned about

The first, and better effect is known as global warming. The sun heats up the earth’s surface by day and this heat is re-radiated during the night. As a greenhouse gas, CO2 reflects this heat back down towards the earth so less is lost to space. More CO2 in the atmosphere equals more trapped heat. This addition of heat energy to the system affects weather patterns (more frequent and severe storms, droughts and floods) and warms the oceans and the atmosphere, contributing to the accelerated melting of glaciers and ice fields (increased sea levels, coastal flooding).

The second effect, of which many people are not aware, is the increase in the concentration of hydrogen ions in the waters of the oceans (ocean acidification). Again, the cause of this acidification is increased CO2 concentration in the waters of the ocean.Without getting too far into the chemistry, acidification of ocean waters is the result of this additional CO2 reacting to form more carbonic acid. An analogy would be the acidity of bottled sodas, caused by the CO2 injected to provide the fizz. The oceans are generally slightly basic, historically exhibiting pH levels of around 8.2 to 8.3. However, since the beginning of the industrial revolution, some 150 years ago, the average pH of the ocean‘s surface layer has declined by about 0.12 pH units, to a value of around 8.1. This may not sound like a big change until you realize that the pH scale is logarithmic and this equates to a 30% increase in the concentration of hydrogen atoms (acidity). Moreover, in geological terms this is a rate of change that is orders of magnitude faster than those that normally occur. As discussed below, marine life has not experienced such a major shift in millions of years and, excluding cataclysmic events such as major outbreaks of volcanism or collisions with asteroids, probably never one that has happened so rapidly. And we are currently doing little to slow this process. Recent estimates show that if we continue to use fossil fuels at current rates atmospheric CO2 levels could reach 500 ppm by 2060 and ocean surface water pH could drop to 7.7 or 7.8, an increase in acidity of 150 %.

Why is this important? First of all, increased acid levels act like a tax levied on most marine life. Most species will be forced to expend more energy simply to maintain the acid balance within their cells, at the expense of growth and reproduction. This is clearly a tax from which they receive no benefits and one which, if it is too high for too long a period will result, at best, in significant decreases in productivity and at worst in the biological equivalence of bankruptcy – death.

In addition, many marine species build skeletons, shells or tests of calcium carbonate. These include the well known corals, the basis for some of the most diverse and spectacular ecosystems in the world. However, many other equally important, if less well known, marine organisms also require calcium carbonate structures. These include many species of marine algae and zooplankton (the food base for many other organisms), most mollusks including one group of small mollusks, the pteropods, which should be of particular interest to Alaskans who like to catch, sell or eat fish. Also known as sea butterflies, these lentil sized sea snails are an abundant and important food source for salmon, herring and cod (and for some whales) in Arctic waters.

Pteropods also are important as a food for many species of fish, whales and penguins in Antarctic waters. A major reduction in numbers or the loss of pteropod populations would have serious effects on our salmon populations as well as on other important species. Recently when scientists subjected some pteropods to pH levels predicted to occur by 2100 their shells showed notable signs of dissolution (Nature. Vol. 437, pp 681-686. 20 September, 2005). Loss or reduction in this group, to say nothing of many other species of calcium dependent phytoplankton and zooplankton that form the very base of the food chain would have effect not only the fish, but the marine birds and mammals of the Arctic sea that depend on fish and other marine life for their existence.

Pteropods, along with the many other calcium carbonate dependent species in the oceans are subject to the negative effects of acidification. The more acidic the water becomes, the harder it becomes for these organisms to build and maintain their skeletons or shells. Recent analyses indicate that Arctic waters are especially susceptible to the negative effects of acidification, with potentially major ecosystem effects if atmospheric CO2 levels are not kept below 450 ppm. As we are currently approaching levels of 400 ppm and with no evidence of a decrease in the rate of CO2 emissions we are dangerously close to the brink in terms of major system disruptions to this area of the ocean including significant loss of fisheries resources.

Perhaps even more disturbing is the evidence from past geological ages when major extinctions occurred. Towards the end of the Permian era, some 250 million years ago (MYA) the largest extinction event of marine life known from the geological record occurred. Some 95% of all marine species disappeared and the seas regained their diversity only after eons had passed. There is increasingly more evidence coming to light that increased CO2, apparently linked to unprecedented levels of volcanic activity leading to massive fires in Canadian coal fields. (see: http://www.eurekalert.org/pub_releases/2011-01/uoc-rfs012111.php ) . During this extinction event, marine organisms with calcareous skeletons or shells were among the most affected species.

Does this mean that we will see a similar extinction event in our near future? No one knows for sure what will happen if we do not address our current rate of increase in atmospheric CO2. However, the evidence we see for acidification that has already taken place and the projected increase in acidity in the near future should be cause for very serious concern. Almost all of the past extinction events that we are aware of, including the Permian event and separate events of 55 and 65 MYA are believed to be linked to major perturbations in the carbon cycle. In each, ocean calcifying organisms were among the species that were most affected.

While past extinction events may not have been solely due to increased CO2 levels and it is possible that multiple factors contributed to these extinctions, neither are we dealing with only one problem in our oceans today. In addition to absorbing significant amounts of the CO2 we are producing, the ocean also is absorbing a lot of the heat. This is one reason the climate effects we have witnessed to date are not more pronounced. However, again this buffering action comes with a cost. Warming of the surface waters of the ocean strengthens the thermal barrier separating nutrient poor surface waters from the fertile layers of deeper water, reducing productivity. Pollution from runoff and discharge of agricultural and industrial wastes effect many marine organisms, and we are now seeing areas of anoxic waters or “dead zones” increasing in size. Overfishing is placing stress of many fish stocks and removal of some keystone species has resulted in major faunal changes, for the most part changes that are not positive in terms of our use of the ocean as a food source.

Some of these problems (overfishing, pollution) are issues we know how to address and it should be simple and non controversial matters for action by our political leaders. The CO2 related problems of warming and acidification, driven as they are by our addiction to fossil fuels, present a challenge of an entirely different order of magnitude. Until the public understands the serious nature of the threat we face it will be difficult to overcome the efforts of the 2,300 or so highly paid lobbyists who seem to have convinced many o f our political leaders that there is no problem . This will require that the public take action. As we have learned over and over again, strong political leadership usually appears only after the politicians see unequivocal evidence that the public is fed up. Once that happens they rush to the front of the parade to lead the charge.

So that is the bad news. However, in an attempt to imitate the extremely effective technique used by Lester Brown (but with no intent to equate my communication abilities or expertise with his) I would like to present a positive pathway for people to consider. Thus, in a follow up article I hope to discuss a number of things we can (and must) be doing to affect the current course we find ourselves on.

Finally, to learn more about the current state of the oceans I recommend that you click HERE.

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Jim Thrall is the Group Coordinator for the Anchorage Chapter of the Citizens Climate Lobby, a non-partisan volunteer citizens lobby group dedicated to creating the political will to achieve a stable climate ( www.citizensclimatelobby.org ).  He is a semi-retired aquatic ecologist with 35 + years experience in preparing environmental assessments, impact statements and mitigation and enhancement plans for resource development projects worldwide, including water resource, mining, and timber harvest developments.  Currently he is continuing to provide consulting services to the Alaska Energy Authority, primarily in assisting them in maintaining their existing hydroelectric projects in compliance with their license conditions.

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