The levels of carbon dioxide in the atmosphere would be much higher if oceans did not absorb the amount they do, but this has led to their rising acidity levels, according to a new United Nations-backed study. Approximately one quarter of the emissions resulting from human activities � including deforestation and the burning of fossil fuels � are taken in by oceans. Without absorption by oceans, atmospheric concentrations of carbon dioxide would be far higher, amplifying the effects of climate change worldwide. But as a result, the chemical balance of oceans has changed dramatically, with scientists predicting acidification will occur at a rate 100 times faster than any change in acidity experienced in the marine environment over the past 20 million years. The rapid pace has left little time for evolutionary adaptation within biological systems. "Substantial damage to ocean ecosystems can only be avoided by urgent and rapid reductions in global emissions of carbon dioxide," said Ahmed Djoghlaf, Executive Secretary of the UN Convention on Biological Diversity. Some 70% of cold water corals, which serve as a feeding ground for commercial fish species, will be exposed to corrosive waters by 2100, the study found.