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Case Study

Global Warming and Ocean Acidification

Figure 5.19
This graph shows the relationship between ocean water pH and the amount of CO2 dissolved in ocean water, both in the past and projected for the future. (Source: Pearson Prentice Hall)

You’ve probably heard the term “global warming” in the news a lot lately. Basically, this term refers to the recent accelerated warming of Earth’s atmosphere and is thought to largely be the result of humans adding carbon dioxide to the atmosphere by burning fossil fuels. Some CO2 in the atmosphere is a good thing – it acts as a “blanket” that keeps the Earth’s surface at livable temperatures. But too much CO2 begins to act like layers upon layers of blankets, making the Earth’s surface very warm. The concentration of CO2 in the atmosphere has risen dramatically in the past 100 years.

As we discovered earlier in this module, gases can be exchanged fairly easily between the oceans and the atmosphere. In regards to CO2, the oceans and atmosphere are in equilibrium with one another. This means that as CO2 in the atmosphere rises, CO2 concentrations also rise in the oceans through their exchanges. In fact, it is estimated that the oceans have taken in more than half of the CO2 that humans have added to the atmosphere!

Your text describes the process by which additional CO2 in the oceans acts to lower the oceans pH – making it more acidic – a process called dissociation. This is done through a series of chemical reactions, each of which release hydrogen ions. But, the oceans have a built-in buffering system – if the water becomes too acidic, the process shown in figure 5.18 in your text reverses itself and takes hydrogen ions out of the water.

Buffering is a bit hard to understand, especially when it involves complex chemistry equations. Think of buffering in this way: Say you decide to enter into a poker tournament with several friends. Because you know you are not very good at poker, you decide to take your rich uncle along to help finance you. In the beginning of the game, you are losing money, but your uncle keeps giving you more so you can stay in the game. Towards the end, you start to get the hang of things, and you start winning money, some of which you give your uncle to pay him back. In this way, your uncle acted as a buffer – he kept you from losing everything you owned in the game!

The problem, scientists believe, is that this buffering process only works well with lower levels of CO2. When the oceans get higher levels of CO2, their ability to buffer is severely diminished. Much like your poker game, if you kept losing and kept losing, you might eventually drain your uncle of money! The result is that the oceans start to become acidic as more and more hydrogen ions are added through the dissociation of CO2.

For a more in-depth look into ocean acidification, check out this fact sheet:
The Dangers of Ocean Acidification.
You are not required to read this document as part of the module content, it is optional.

And acidification, as you can imagine, can have detrimental effects on marine life. Most marine organisms are used to the relatively stable pH of the oceans, and any change in this could upset their biological balance. Scientists are only beginning to research the effects of acidification, but already have determined that it could seriously effect both corals and shelled species. This is because both make their protective coverings with calcium carbonate – a substance that would easily dissolve in acidic waters.

Of course, this is just one of many of the effects of increasing CO2 in the atmosphere – and the global warming it causes – on our oceans. We will discuss climate change more in later modules and also use the case studies to examine some of these effects in more detail.

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