The world's oceans are becoming warmer and more acidic. This will lead to mass extinctions this century, even if carbon dioxide emissions are cut.
The oceans are more acidic now than at any point in the last 300-million years. The blame lies firmly with human emissions of carbon dioxide from burning fossil fuels. The mass extinction of species in the ocean could already be inevitable as a result.
These are the findings of a report by the International Programme on the State of the Ocean. "State of the Ocean Report 2013" was published in the peer-reviewed journal Marine Pollution Bulletin.
It warned: "The risks to the ocean and the ecosystems it supports have been significantly underestimated. Marine degradation is happening much faster than previously predicted." It revised previous predictions, saying that the scale of impacts would be larger and the timescale much shorter than previously thought. The report is published every two years.
"This is unprecedented in the Earth's known history. We are entering an unknown territory of marine ecosystem change, and exposing organisms to intolerable evolutionary pressure. The next mass extinction may have already begun," it said.
Alex Rogers, one of its authors and a professor of biology at Oxford University, said, "The health of the ocean is spiralling downwards far more rapidly than we had thought. The situation should be of the gravest concern to everyone since everyone will be affected by the changes in the ability of the ocean to support life on earth."
Pledges by world governments
The current pledges by world governments to cut carbon emissions – a binding agreement will only go into effect in 2020 – will not be enough to save many of the world's reefs. The increased acidity dissolves the calcium carbonate that creates coral. It also kills phytoplankton, which produce 40% of the oxygen in the atmosphere.
Because there is a time lag between carbon emissions and the impact on the oceans, the effects will be felt slowly at first and will be hard to stop once the change has begun, it said. Carbon emissions have to peak at a maximum of 450 parts per million and then go down, warned the report.
"For the most part, the public and policymakers are failing to recognise, or choosing to ignore, the severity of the situation and are not taking the action necessary to address it," the report said.
The less obvious changes are equally serious. As the chemical composition of the ocean changes, so species are unable to adapt quick enough. Those that use chemical signals to help them understand their surroundings are now having problems finding prey and hunters.
Co-chair of the programme Trevor Manuel said that if the Intergovernmental Panel on Climate Change (IPCC) report was a wake-up call on climate change then the International Programme on the State of the Ocean is a deafening alarm bell on humanity's wider impact on the global oceans.
As the world's population increases to nine-billion people, the oceans would be critically important to feeding people.
If nothing is done, there will be a profoundly negative impact on prosperity and wellbeing. "Governments must respond as urgently as they do to national security threats. In the long run, the impacts are just as important," he said.
The report also found that the oceans are under serious threat as a result of human activity, with 70% of the world's fish populations overexploited. By 2100 the oceans would have also lost 7% of their oxygen content.
Last week's IPCC report found that the oceans have absorbed a third of the carbon that humans have emitted. This has slowed the impact on the earth but the change is "progressive and relentless".