What causes ocean acidification?
Ocean acidification is mainly caused by carbon dioxide gas in the atmosphere dissolving into the ocean. This leads to a lowering of the water's pH, making the ocean more acidic.
Many factors contribute to rising carbon dioxide levels. Currently, the burning of fossil fuels such as coal, oil and gas for human industry is one of the major causes.
Deforestation results in fewer trees to absorb the gas. Also, when plants are cut down and burnt or left to rot, the carbon that makes up their organic tissue is released as carbon dioxide.
Some parts of the ocean are naturally acidic, such as at hydrothermal vent sites - underwater 'hot springs'.
In the past, ocean acidification occurred naturally but over much longer periods of time. It is occurring faster now than in the last 20 million years.