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.
"Ocean acidification is yet another red flag being raised, carrying planetary health warnings about the uncontrolled growth in greenhouse gas emissions," said Achim Steiner, the executive director of UNEP. "It is a new and emerging piece in the scientific jigsaw puzzle, but one that is triggering rising concern."
Oceans absorb some 25 percent of global CO2 emissions, but once they do so, the carbon dioxide is transformed into carbonic acid, which accounts for the precipitous fall in pH levels found by the study. It is unclear, however, what exactly the effects of the increase in acidity might be for ocean life, but scientists are concerned that the change may harm many shell-building organisms at the bottom of the food chain.
"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.
But its not just global warming that is damaging fish stocks in the oceans. According to a separate report released on Thursday by the University of British Columbia in Canada, the total global catch quintupled between 1950 and 1987, primarily the result of a rapid and expansive increase in fishing grounds. Since then, however, expansion has slowed and the total catch has levelled off, and even dropped slightly from the peak of 90 million tons per year.
The study found that a third of the world's oceans and two-thirds of coastal waters are now being exploited, with the only frontiers left being relatively unproductive waters on the high seas and the coastal regions of the Arctic and Antarctic, both difficult to access. The study concludes that, if fish is going to remain a major part of the global diet, sustainable methods must be rapidly introduced to counteract the natural limits that may now have been reached.
"The decline in spatial expansion since the mid-1990s is not a reflection of successful conservation efforts but rather an indication that we've simply run out of room to expand fisheries," said study author Wilf Swartz in a press release.
Co-author Enric Sala adds: "The era of great expansion has come to an end, and maintaining the current supply of wild fish sustainably is not possible."