Covering more than 70% of the earth’s surface, the oceans contain 99% of the living space on our planet. But this vast body of water is being altered by our actions on land and in the air. Carbon dioxide (CO2) emissions from the combustion of fossil fuels, industrial processes and large-scale changes in land use are contributing to global change in the terrestrial and marine biospheres. Currently we’re adding an extra 36 billion tonnes of CO2 to the atmosphere every year.
The oceans are in balance with the atmosphere and act like a giant sponge, absorbing CO2 from the air. Since the beginning of the Industrial Revolution, they have absorbed approximately one-third of all human CO2 emissions. Although this helps to remove CO2 from the atmosphere and so reduce greenhouse gas effects such as warming, CO2 in the oceans creates other problems. Once in sea water, CO2 dissolves like gas in a fizzy soft drink. We all know that fizzy soft drinks are acidic and can corrode our teeth. This same chemical process is happening in our oceans. When we record the pH (a measure of acidity) in our oceans now, we can see that they have become more acidic by 0.1 units. This may not sound like much, but pH is measured on a logarithmic scale, so a difference of 0.1 units actually means this extra CO2 has already made the oceans 30% more acidic than they were 250 years ago. This process is called ocean acidification.
Right now, ocean chemistry is changing 100 times faster than at any period in the past 650,000 years. Projected changes in ocean pH are greater and far more rapid than any experienced in the past 24 million years and possibly the past 300 million years. If we continue our business-as-usual CO2 emissions, in just 85 years – at the end of the century – the oceans will be 100–150% more acidic than they were before the Industrial Revolution.
Giant clams can weigh up to 300 kilograms. Sue-Ann is trying to predict how they will fare as our oceans become more acidic in a warming world, creating a hostile environment for animals that have calcium carbonate shells.