Melting glaciers. Disappearing coastlines. Extreme weather. Climate scientists have been warning for years about the possible effects of global warming -- and have a long list of future horrors in store for mankind.

Some effects of climate change, however, are more difficult to see. And with representatives from around the world currently gathered in Cancun, Mexico in yet another attempt to forge an international agreement on how best to tackle the climate problem, the United Nations on Thursday released a study pointing to one of those less visible catastrophes: the state of the world's oceans.

According to the report, released by the UN Environmental Program (UNEP), the chemistry of the oceans is changing at a rate not seen for 65 million years. Should the rate of change continue unaltered, our oceans could be 150 percent more acidic by the end of this century, the study says.

"We are seeing an overall negative impact from ocean acidification directly on organisms and on some key ecosystems that help provide food for billions," said Carol Turley, the lead author of the new report, in a press release. Furthermore, according to the study, an increase in acidification could have a devastating effect on coral reefs, which provide a home for 25 percent of all marine species and provide food and jobs to some 500 million people around the world.

(Source: Oceans Threatened by Rising Acidity and Overfishing [Der Spiegel])