A delicate balance: rising acidity in our oceans is putting marine ecosystems at risk.

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Increasing ocean acidity is rapidly damaging marine ecosystems, and urgent action is needed to limit its effects, according to the world's top ocean scientists.

More than 150 leading scientific experts expressed their concern by signing the Monaco Declaration, a document calling for global action and outlining the efforts needed, released last Friday.

The Declaration is based on results from the Second International Symposium on the Ocean in a High-CO₂ World, held in Monaco last October, which emphasised the clear-cut ties between rising ocean acidity and rising carbon dioxide emissions.

"The ocean now absorbs about 30 per cent of the yearly emissions of carbon dioxide, which dissolves in water to form a weak acid that is increasing the acidity of the oceans...[and this] carbon dioxide uptake is occurring at a rate exceeding the natural buffering capacity of the ocean," explained Tasmanian oceanographer Will Howard, from the Antarctic Climate and Ecosystems Cooperative Research Centre in Hobart.

As such, unlike global warming, which is an indirect effect of greenhouse emissions, "ocean acidification is a direct impact from rising atmospheric CO₂ levels," said Ben McNeil, an Australian signatory of the Declaration from the Climate Change Research Centre, at the University of New South Wales in Sydney.

"[It] is yet another reason why it is in our best interests to stabilise atmospheric CO₂ levels by rapidly cutting our...emissions over the coming decades," he said.

Inhospitable reefs by 2050?

Controlling ocean acidity is fundamental to keeping marine environments healthy and functioning.

Acidification is currently reducing the availability of carbonate ions, for example, used for by a host of marine creatures, including coral, to grow and build shells.

Researchers are already observing changes in skeletal structures and coral growth rates as a result, and if atmospheric CO₂ continues to rise, ocean acidification could render most regions of the ocean inhospitable to coral reefs by 2050.

It could also lead to substantial changes in commercial fish stocks, threatening food security for millions of people, as well as the multi-billion dollar fishing industry.

Limiting future carbon dioxide emissions is the only way through which acidification can be controlled, the Declaration warns, and that it should not be considered "a peripheral issue".

"It is the other CO₂ problem that must be grappled with alongside climate change. Reining in this double threat, caused by our dependence on fossil fuels, is the challenge of the century," it reads.

Though solving the problem will require "a monumental world-wide effort", there remains hope, the scientists agree.

"[P]artial remedies already on the table, if implemented together, could solve most of the problem," the Declaration says, but "we must start to act now because it will take years to change the energy infrastructure and to overcome the atmosphere's accumulation of excess CO₂."

"I strongly support this declaration", said Prince Albert II of Monaco, whose environmental foundation provided support for the symposium. "I hope the declaration will be heard by all the political leaders meeting in Copenhagen in December 2009 [at the United Nations Climate Change Conference]."