Ocean acidity Q&A: scientists warn of growing threat to life

The acidity of the world’s oceans is increasing at an “unprecedented rate”, scientists say, warning that seawater will be 170 per cent more acidic by 2100 if current trends continue.

The study was led by the International Biosphere-Geosphere Programme, and follows a meeting of 500 of the world’s leading experts on ocean acidification last year. Their findings will be formally presented in Poland next week.

What is happening?

The BBC reports a fundamental change in the chemistry of the world’s oceans, which have become 26 per cent more acidic since the start of the industrial revolution. Earlier this month, the International Programme on the State of the Ocean found that the rate and speed of change in the ocean was greater than previously thought, and warned that some seawater will become uninhabitable for some organisms within decades.

Why are acidity levels rising?

The authors of the State of the Ocean report say, with “very high confidence”, that acidification is being caused by carbon dioxide emissions resulting from human activity. They say these changes are already measurable, and that the legacy of fossil fuel emissions will be felt for centuries.

Why is increasing acidity a problem?

Acidification matters not just because it changes the pH level of the ocean, but also because of the impacts it would have on the ecosystem. Many shell-forming marine organisms are very sensitive to changes in pH, while acidification also harms marine creatures that rely on calcium carbonate to build coral reefs. An expert quoted by the BBC said that molluscs would struggle to survive at the pH level predicted for 2100. Professor Jean-Pierre Gattuso of the French national research agency CNRS warns that changes to tiny organisms and molluscs can have a “cascading impact on the whole food chain.”

What are the potential consequences?

Professor Gattuso says some of the effects of rising acidity are already being seen in pteropods – sea snail-like organisms – in the Southern ocean, which have suffered shell erosion. The Arctic and Antarctic are currently suffering most from rising acidity, since cooler waters there hold more carbon dioxide. By 2020, scientists expect that species which build their shells from calcium carbonate will retreat from the polar regions. By 2100, the predicted acidity levels would affect tropical coral reefs as well as colder waters. The authors of the State of the Oceans study say the knock-on economic effects could be huge. Ban Ki-moon, the Secretary General of the UN, has described oceans as “integral to all of humanity” and said that their degradation would influence virtually all aspects of life on the planet.

What is the evidence for these predictions?

Scientists can predict what might happen if a certain level of acidity occurred by studying areas – such as those near CO2 vents and volcanoes – that already have raised levels of acidity. Research at these deep sea vents suggests that around 30 per cent of the ocean’s biodiversity could be lost by the end of this century if this pace of change continues.

What can be done to address the problem?

Scientists say that reducing CO2 emissions is “the only way to minimise long-term, large-scale” risks associated with acidification. Wendy Broadgate, the deputy director of the International Geosphere-Biosphere Programme, told website Science Daily that reducing other “stressors” such as pollution and overfishing, could help to reduce the impact of ocean acidification by building resistance into the ecosystem. Experts say that attempts to reduce ocean acidity by adding large volumes of crushed limestone to the water would be expensive and impractical on the necessary scale. The UN says that there is currently “no global international instrument specifically dedicated to addressing ocean acidification”, but that the Convention of the Law of the Sea requires states to protect and preserve the marine environment. · 

The Week, 14 November 2013. Article.

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