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Sea Levels to Reach Pliocene Levels

Current climate predictions resemble a new reconstruction of carbon dioxide fluctuations from the Pliocene epoch around three million years ago, when the Earth was most recently warmer than today. The new data, published in Nature, was used to estimate the sensitivity of climate to increasing levels of carbon dioxide.

“We are headed towards a climate like the Pliocene, where there is a mean warming of around 2.5 to 3 degrees,” said Prof Eelco Rohling of The Australian National University. “The scary bit is that Pliocene sea level stood at least 9 metres higher than today.”

During the Pliocene, atmospheric carbon dioxide levels were around 350–400 parts per million, similar to levels reached in recent years. “Our current study finds that modern climate is as sensitive to carbon dioxide change as the Pliocene climate,” Rohling said. “Therefore, we may expect ice-sheet retreat and sea-level rise to continue toward similar values over centuries to come.”

The study deduced carbon dioxide levels by examining boron levels in microfossils sampled from the ocean floor. Changes in ocean acidity affect the ratio of boron isotopes that various marine organisms take up in their shells.

“Today the Earth is still adjusting to the recent rapid rise of carbon dioxide caused by human activities, whereas the longer-term Pliocene record documents the full response of carbon dioxide-related warming,” said joint lead researcher Dr Gavin Foster of the University of Southampton.

Rohling said that sea level rises will depend on delayed response of the ice sheets to the sudden rise in carbon dioxide. “This is a game that plays over centuries; it does not stop at the much-debated year 2100,” he said.

“It’s inevitable. It could take the Earth 200,000–300,000 years to clean up the carbon we’ve emitted.”