The other CO2 problem is in our oceans

Climate change is fundamentally a story about water. Whether it’s prolonged droughts, severe floods, changing rain and snowfall patterns, or melting glaciers and ice caps — the ways in which humanity will experience and suffer most from climate change is most related to how rising greenhouse gas emissions will impact Earth’s water resources.

In the ocean, the negative impacts are already dramatic and undeniable. The ocean is getting warmer and sea levels are rising. These changes can only occur on a global scale if the planet is warming up significantly. But rising carbon dioxide levels pose another massive threat to the health of the ocean — a phenomenon known as ocean acidification.

When carbon dioxide (CO2) is emitted into the atmosphere it doesn’t just stay there — about 25 per cent of emissions are absorbed into the ocean. Scientists once thought this was beneficial as that carbon dioxide would otherwise accelerate global warming even more. However, it turns out we have instead created an entirely new problem. That’s because as CO2 builds up in the ocean, it causes alkaline seawater to acidify. An ocean increasing in acidity is not a very friendly place for a wide range of creatures, many of which play critical roles in marine food webs and are vital sources of human food.

I recently travelled to Italy and across North America investigating how ocean acidification could impact marine life. While I like to remain hopeful in most things, what I learned has made me very worried about the future of the ocean. Whether I was talking to shellfish farmers in the Pacific Northwest who have already lost millions of dollars from die-offs in their hatcheries or meeting scientists studying the dissolving shells of tiny creatures called pteropods, it soon became evident that ocean acidification is not some far off event — it’s happening right now.

When CO2 enters the ocean it reacts with seawater to form a chemical compound called carbonic acid. The more carbonic acid, the more hydrogen ions get released into seawater, thus increasing its acidity. A confusing aspect of this issue, which requires some counterintuitive thinking, is that the ocean is not acidic. Seawater will always remain alkaline but as more and more CO2 enters the ocean, the pH of seawater is lowering, causing it to become less alkaline or increased in acidity.

But hydrogen ions don’t just increase acidity; they also attach themselves to a chemical compound called calcium carbonate, which is the vital building block for the strong shells of marine organisms from oysters and clams to lobsters, snails, sea urchins and corals. If you eat seafood, most of what you eat either needs to absorb calcium carbonate into their body or preys on something else that does.

For most of human history, ocean pH has been fairly stable. Yet, since the industrial revolution, humans have emitted approximately 375 billion tons of CO2 into the atmosphere, a quarter of which has been absorbed into the ocean. This excess CO2 has caused the average pH of the surface ocean to decrease from 8.2 to 8.1 units, which unfortunately translates into a 30 per cent increase in acidity!

Using business as usual rising emission trends, scientists have estimated that by the end of the century the surface waters of the ocean could be nearly 150 per cent more acidic. This would be very bad news for shelled organisms, most importantly corals who require calcium carbonate to build their skeletons and form reefs, habitats that support 25 per cent of all marine life and for us.

But you don’t need a shell to be disturbed by ocean acidification. Recent studies have shown that even fish and squid are affected by acidification because they have organs in their bodies made of calcium carbonate. Of course, not all species will suffer. Organisms like jellyfish are virtually unaffected by changes in seawater chemistry and many ocean plants and seaweeds absorb CO2 so they should mostly do just fine. Unfortunately, not many humans are scrambling to eat jellyfish and seaweed sandwiches.

While it is still difficult to predict exactly how marine life will cope as our oceans continue to acidify, we know it won’t be good because this phenomenon has happened before. During two extinction events that took place millions of years ago, ocean acidification was one of the major factors responsible for extinctions of marine life, including during the Permian Triassic Extinction event when 96 per cent of all life in the ocean died out. The big difference now is that our current ocean acidification event is occurring at least 10 times faster than it did during those extinction events, or any other time in the last 300 million years.

So what do we do about it? Actions like reducing overfishing and marine pollution will help restore marine habitats and help organisms adapt to this level of change. It has been suggested that spreading algae and seaweed farming on a massive scale to produce biofuel could help absorb excess CO2 in coastal waters and slow acidification. But there really is only one effective measure if we want to prevent possible extinctions of marine life and that is to dramatically reduce our CO2 emissions.

There are not a lot of reasons to be optimistic about the future of our acidifying oceans, but one ray of hope I get from this issue is that I truly believe that ocean acidification can be used to convince climate deniers that there are consequences to carbon pollution. Ocean acidification can only happen because of increased CO2 concentrations in the ocean and this process can only be explained by irrefutable principles of chemistry. While it is impossible to pinpoint any particular violent storm or individual weather pattern on atmospheric CO2 concentrations, with acidification there can only be one explanation. So next time you hear someone expressing doubt about the dangers of climate change, let them know about ocean acidification.

Alex Mifflin, The Huffington Post, 15 May 2015. Article.

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