Acidity in seas to reach levels not seen in 14 million years

About 22 million tonnes of carbon dioxide is absorbed by the oceans every day. Picture: contributed

The world’s oceans will be more acidic by the end of this century than at any time in the past 14 million years due to the impact of human-induced climate change, according to earth scientists.

They say the scenario would pose a major threat to marine life, with the shells of some sea creatures already dissolving in increasingly acidic conditions.

Ocean acidification occurs when carbon dioxide from the atmosphere is absorbed by seawater, resulting in a lower pH.

New research led by Cardiff University has shown that ocean acidification is likely to hit unprecedented levels in the next few decades if greenhouse gases emission continue at current levels.

Around a third of the carbon dioxide released by burning coal, oil and gas gets dissolved into the oceans.

Since the beginning of the industrial era, around 525 billion tonnes has been absorbed.

That equates to around 22 million tonnes worldwide every day.

Study leader Dr Sindia Sosdian, from Cardiff University’s School of Earth and Ocean Sciences, said: “Our new geological record of ocean acidification shows us that, on our current business-as-usual emission trajectory, oceanic conditions will be unlike marine ecosystems have experienced for the last 14 million years.”

Co-researcher Professor Carrie added: “The current pH is already probably lower than any time in the last two million years.

“Understanding exactly what this means for marine ecosystems requires long-term laboratory and field studies as well as additional observations from the fossil record.”

In the study, the academics set out to reconstruct levels of ocean acidity and atmospheric carbon dioxide levels over the past 22 million years.

They did so by analysing the fossils of tiny marine creatures that once lived near the ocean surface, specifically using the chemistry of their shells to monitor the acidity of the seawater in which they lived.

Based on this information, the researchers were able to put their new records of pH and carbon dioxide levels in context of the range of future carbon emission scenarios that are recognised by the Intergovernmental Panel on Climate Change.

In a future where emissions continue at same rate as today, atmospheric carbon dioxide would be near 930 parts per million in the year 2100. Current levels stand at around 400 parts per million.

Similarly, the pH of the oceans would be less than 7.8 in 2100, compared to around 8.1 now.

This is very significant, they say, as the pH scale is logarithmic. It means a drop of just 0.1 pH units represents a 25 per cent increase in acidity.

The levels of atmospheric carbon dioxide and ocean acidity predicted have not been since the Middle Miocene Climatic Optimum period, around 14 million years ago, when global temperatures were around 3°C warmer than today as a result of the earth’s natural geological cycle.

The study was funded by the UK’s Natural Environmental Research Council.

Researchers from the University of St Andrews, the University of Southampton and the University of California also worked on the project..

The study is published in the journal Earth and Planetary Science Letters.