Coral, shellfish and thousands of other species are in danger because the sea is becoming increasingly acidic, scientists warned today.

A Royal Society report said carbon dioxide (CO₂) emissions are making the oceans increasingly acid, a similar reaction to that which causes acid rain.

The report said the oceans are now on an irreversible path which will mean that by 2100 seawater will be more acidic than for hundreds of millennia.

The report authors said it was further evidence for world leaders meeting at the G8 Summit in Scotland next week to cut emissions to less than half what they are today – which is well beyond the scope of the Kyoto protocol.

Oceans act as a giant sponge, taking up carbon dioxide from the atmosphere which dissolves and forms an acid in seawater.

Over the next hundred years, the oceans will become more acidic by 0.5 of a Ph unit on the 14-point scale, according to the report.

Sea creatures such as corals, shellfish, sea urchins and starfish will suffer most because acidity levels will make it harder for them to form their skeletons and shells.

By 2050 corals could be rare on tropical and sub-tropical reefs including the Great Barrier Reef, with knock-on effects for hundreds of thousands of species and people.

The worst effects are expected to be in the Antarctic Ocean where tiny shelled plankton which cover vast areas could be the first victims, causing problems for the animals that feed on them.

High CO₂ levels may also make it harder for fish and other large marine animals to obtain oxygen from seawater.

Squid will be worst affected because of their energy-demanding method of swimming.

Professor John Raven, chair of the Royal Society working group on ocean acidification said: “Our world leaders meeting at the G8 Summit must commit to taking decisive and significant action to cut carbon dioxide emissions.

“Failure to do so may mean that there is no place in the oceans of the future for many of the species and ecosystems that we know today.

“Basic chemistry leaves us in little doubt that our burning of fossil fuels is changing the acidity of our oceans.

“The rate change we are seeing to the oceans’ chemistry is a hundred times faster than has happened for millions of years and we just do not know whether marine life, which is already under threat from climate change, can adapt to these changes.”

Since the Industrial Revolution the oceans have absorbed about half of the carbon dioxide produced by humans burning fossil fuels. They are currently taking up one tonne of CO₂ emissions for each person on the planet every year.

The report looked at the feasibility of adding limestone to the oceans to make them more alkaline, reversing the effect of fossil fuel burning.

But it found that the vast quantities involved made the suggestion impractical.

Scientists are continuing to investigate the possibility of carbon capture and storage – which would see CO₂ emissions collected at source and then stored for thousands of years, possibly in liquid form, on the seabed in the deep oceans or underground.

Professor Andrew Watson, who sits on the Royal Society working group, said that to alleviate the situation CO₂ emissions needed to be cut to less than half today’s levels by 2100, well beyond Kyoto levels.

• scotsman.com