 One of the most significant features of our planet is the fact that 70% of its surface is covered by an ocean. In raw economic terms, the goods and services provided by oceans represents more than 20 trillion US dollars each year. Coral reefs are one of the jewels of the ocean. Despite representing less than 0.1% of the Earth's surface, coral reefs generate 29.8 billion US dollars each year in terms of net benefits and support an estimated 850 million people, many of whom depend on reef organisms for their daily protein. But the biological bounty of our oceans is dependent on the temperature and concentration of carbon dioxide. As you will see, what appears to be small changes in ocean acidity, as measured in pH units, in combination with rising temperatures, can have a huge impact on ocean ecosystems, which ultimately affect millions of people. As humans have added carbon dioxide to the atmosphere, an increasing amount has been absorbed by the upper layers of the ocean. This has caused a phenomenon known as ocean acidification. So far, around 30% of the carbon dioxide emitted into the atmosphere by humans has been absorbed by the ocean. Once carbon dioxide dissolves in the ocean, a number of chemical reactions take place. Up front, there's an increase in hydrogen ions, which manifests itself as a reduced ocean pH. Then some of those hydrogen ions react with carbonate ions to form bicarbonate ions, thereby reducing the concentration of carbonate ions. Now carbonate ions are important for calcification, the process by which marine animals and plants build their skeletons and shells. Hence any decrease in carbonate ions makes calcification much more difficult. So adding carbon dioxide to the atmosphere decreases the pH and the concentration of carbonate ions and then this then leads to a decrease in calcification and a range of other negative effects on the calcium carbonate balance of coral reefs. Another part of the chemistry associated with ocean acidification is the fact that it takes tens of thousands of years to reverse. The only way the ocean can get less acidic is from the erosion of materials from rocks on land that are washed into the ocean. It's sobering to think then that the bad decisions that we are making today when it comes to ocean acidification will have consequences for at least the next 300 generations of humans. How are we so sure that the ocean is acidifying? Well, the theoretical chemistry behind the effective carbon dioxide on oceans has been known for at least 100 years. Based on carbon dioxide levels in the atmosphere, ocean pH should have decreased by 0.1 units since the beginning of the industrial period. This may seem like an impossibly small amount of change but the pH scale is exponential. A 0.1 decrease on the pH scale translate to about a 26 percent decrease in carbon ion concentrations dramatically changing the availability of this important iron. Ocean acidification has been confirmed by measurements taken by oceanographers. Here is just one dataset confirming those chemical changes in the ocean as a result of rising carbon dioxide. Carbon dioxide in the ocean, shown in blue, is rising as carbon dioxide in the atmosphere, shown in red, is increasing. Ocean pH, shown in green, is steadily decreasing. This is what science has predicted. Studies of past ocean pH are also giving us some interesting insights. Ocean pH, it turns out, has been stable for a long time but there have been periods in Earth's history when it was lower than it is today. This is a figure that pulls together our understanding of how ocean pH has varied over the past 400 million years. The green and the blue lines are from the past with the decrease being due to high levels of CO2 in those earlier atmospheres. When you compare those periods with values from today, shown in gray, you can see how different the world's oceans were at those earlier times. Note however that the red line shows where we are headed if we continue on the current carbon dioxide emission trajectory. Talk about back to the future. It's also crucial to note that the rate at which we're changing ocean chemistry is extremely high. There is now overwhelming evidence that the current rate of change in ocean pH is faster than any other time in the past 65 million years if not the past 300 million years. Now given the well-known sensitivity of marine life to changes in pH and carbon at iron concentration, this represents a serious challenge to the biology of life in the ocean. And this is a challenge that we've been exploring at the University of Queensland. In an experiment with Associate Professor Sophie Dove and our research team on Heron Island, we've exposed small sections of coral reefs growing under different scenarios of the future. That is under different amounts of change with respect to temperature and carbon dioxide. Some of our tanks were exposed to a reduced emissions future, others to conditions consistent with the business as usual future that we're currently on. We've also looked at what would happen if we had not polluted the atmosphere with carbon dioxide in the first place and this treatment we refer to as the pre-industrial treatment. This is essentially the world that Darwin and other early scientists saw. We compared each of these treatments to present-day treatments. This is corals growing under current conditions. Take a look at these videos to see what happened in the four treatments over the course of several months at Heron Island. Well as you see the top two conditions are pre-industrial and present-day treatments maintained healthy corals and other organisms. The bottom two conditions however reveal a complex set of changes. With mild increases in carbon dioxide and temperature, typical of a reduced emissions future, only a few corals and other organisms survived. It's not pretty but reefs like this may well be able to recover if we stabilize ocean conditions in the long run. In the business as usual future, in the bottom right however, where carbon dioxide and temperature increase dramatically, no corals survive. This is a future where the marine resources that support people today will have largely disappeared. Looking back over the geological record it's apparent that corals have survived periods of Earth's history when conditions were warmer and more acidic than today. Now this can lead to the myth that things are okay because coral reefs were eventually returned. However this is very misleading. It ignores the fact that recovery after a mass extinction event takes a very long period of time. For example the last mass extinction event that took out the dinosaurs also affected corals so strongly that it took coral reef ecosystems about 10 million years to recover. 10 million years is about 40 times the length that our species has been in existence on this planet. Many scientists believe that humans are driving another mass extinction event from which it will also take a similarly long time to recover. So try telling that to the tour guides on the Great Barrier Reef that there's no need to worry about climate change because coral reefs will eventually come back in a few hundred generations. So in summary there are real concerns about ocean certification based on real-time experiments models and lessons from the past. Given this it's very puzzling why some people focus on the name ocean acidification in order to distract from the issue. This particular myth says that because the ocean is not acidic and that it is not going to get acidic anytime soon ocean acidification must be a lie. This myth is a misrepresentation of the situation. To understand this distraction let's have a look at the pH scale. As you can see basic or alkaline conditions range from 14 down to 7 on the pH scale and acidic conditions range from 7 down to 0. The pH of the ocean is approximately 8.1 so it's correct to say that the ocean is not acidic. However we know from direct measurements of the ocean that the pH is decreasing which is referred to as acidification. We are essentially taking an alkaline ocean and are moving it in the direction of acidity. Now this is just like adding cold water to a hot bath and calling it cooling but the bath will still be warm even though we've cooled it with cold water. Consequently saying that ocean acidification is a lie is a misrepresentation. It focuses on semantics rather than the physical reality of ocean becoming more acidic as carbon dioxide floods into it from the atmosphere and this completely ignores the fact that ocean acidification is a really big issue. While we have much to learn the evidence shows that the changes that we're inflicting on the ocean and its biology and the hundreds of generations of people to follow are potentially very serious and represent an experiment that we should not be conducting on ourselves let alone our planet.