The oceans cover more than two-thirds of the planet earth. This vast body of water absorbs about one third
of human-generated carbon dioxide (CO2), thus, a smaller amount of this greenhouse gas remains
in the atmosphere and global warming is slowed. However, in the ocean the carbon dioxide reacts to
form carbonic acid. The water turns more acidic and becomes a threat to big and small marine organisms.
Since the Industrial Revolution of the mid-19th century, the human population has released around 440 billion tons of carbon dioxide (CO2) into the atmosphere from the burning of fossil fuels such as coal, natural gas and crude oil – equivalent to 440 million return flights from Germany to Australia!
|The global carbon dioxide budget for the years 1990 to 2000 (blue) and 2000 to 2009 (red), expressed in
gigatons per year. Graph: Katharina Marg, formkombinat.
Plants process this invisible and odourless gas into oxygen through photosynthesis. The oceans also act as "CO2
sinks" by binding carbon dioxide. If these natural stores on our planet did not exist, it would heat up much more
and much faster than what we observe today. Carbon dioxide is a dangerous greenhouse gas: Once it gets into
the atmosphere, it reflects heat radiated from the earth and the climate starts to heat up.
The oceans slow down this global warming, however, the CO2 from the atmosphere reacts with seawater to form carbonic acid. As a result, the pH of the water decreases – it becomes more acidic.
Experiments and numerical model calculations clearly indicate that increasing carbon dioxide concentrations and the resulting ocean acidification have consequences for marine life: Corals, sea urchins, mussels and snails, as well as smaller organisms that build their skeletons and shells from calcium carbonate, will not be able to develop as they did before. In the Antarctic Ocean, researchers have already discovered plankton, whose shells are 35 per cent lighter than comparable specimens recovered from sediment cores dating back to times prior to industrialisation. These microscopic organisms will be the first ones affected by ocean acidification. Plankton sits at the base of the food chain and serves as food for fish and other larger animals. In addition, their metabolism influences important chemical processes in the ocean. Ocean acidification disturbs the balance in these systems. It is still unclear what this means for our climate and our environment, therefore, scientists are working hard to better understand the process of ocean acidification and to better estimate its consequences.