Acidification of the oceans

The oceans absorb around a third of the 20 billion tonnes of carbon dioxide produced each year by human activity. While the process helps to slow global warming by keeping the gas from the atmosphere, in sea water it dissolves to form carbonic acid - rising levels of which cause carbonates to dissolve.

Aragonite is a vital mineral for corals and other marine organisms needed to grow their skeletons. Aragonite is particularly susceptible to carbonic acid. Without it, corals become brittle and are unable to grow and repair damage caused by fish, snails and natural erosion. Unfortunately, human activities, including those associated with global warming, are threatening this precious environment. Increasing sea temperatures stress corals and cause damage, including bleaching.

Some scientists from Britain, the US and Australia, working with teams from the UN and the World Bank have voiced concerns that 98% of the world's reef habitats are likely to become too acidic for corals to grow by 2050.

The loss of big coral reefs would have a devastating effect on communities, many of which rely on fish and other marine life that shelter in the reefs. It would leave coastlines unprotected against storm surges and damage often-crucial income from tourism. Among the first victims of acidifying oceans will be Australia's Great Barrier Reef, the world's largest organic structure.