More than a quarter of the carbon dioxide we release into the atmosphere every year is soaked up by the oceans. Initially, this may appear to be a good thing, tempering global warming, but there is a downside. As more carbon dioxide dissolves into the oceans, the more acidic the seawater becomes. Over the next century, ocean acidification has the potential to alter many marine ecosystems so that sea life is affected as well as fisheries – a basic food source on which many rely.