Scientists have suggested that ocean acidification may hit levels never seen before if we continue on the current trend of carbon emissions.

Publishing their research in the journal Earth and Planetary Science Letters, the team from Cardiff University in Wales reconstructed levels of ocean acidity and atmospheric CO2 over the last 22 million years. And they found we may be approaching levels that have not been seen for millions of years.

"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," Dr Sindia Sosdian, lead author of the study, said in a statement.

Ocean acidification is the result of CO2 from the atmosphere being absorbed by seawater, lowering the pH of the water. About a third of all CO2 released from burning fossil fuels gets dissolved in the ocean, resulting in about 525 billion tons being absorbed since the dawn of the industrial age, or 22 million tons a day.

Looking at the fossilized shells of small marine creatures, the team were able to trace back the levels of acidity in seawater. They noted that the pH of ocean water today was about 8.1, but by 2100 – if CO2 levels rose to 930 from 400 parts per million today and if the current trend continued – this would drop to 7.8. Each drop of 0.1 corresponds to a 25 percent increase in acidity.

The last time Earth’s oceans were this acidic was in the Middle Miocene Climatic Optimum period, which occurred about 14 million years ago when Earth was roughly 3°C (5.4°F) warmer due to natural changes. It’s important to make clear that is not the case this time around. Human activity is causing a rapid warming of Earth’s climate as more carbon dioxide is released.

"The current pH is already probably lower than any time in the last 2 million years,” Professor Carrie Lear, a co-author on the study, said in the statement. “Understanding exactly what this means for marine ecosystems requires long-term laboratory and field studies as well as additional observations from the fossil record."

And that poses all sorts of problems. Ocean acidification directly affects coral reefs, causing them to grow more slowly or even dissolve. Last year, meanwhile, an eight-year-long study found that all marine life will be impacted by ocean acidification, either directly or as a result of impacts to their habitat or food.