Carbon dioxide levels in the atmosphere will overtake those seen 3.3 million years ago by 2025, predicts study

During the warmest phase of the Pliocene epoch, it had between 380 and 420 parts per million carbon dioxide circulating in the atmosphere, which is close to the current estimate of 415 parts per million


                            Carbon dioxide levels in the atmosphere will overtake those seen 3.3 million years ago by 2025, predicts study
(Getty Images)

The Earth is witnessing a part of its history repeat itself. The current levels of the heat-trapping gas — atmospheric carbon dioxide — has reached those seen 3.3 million years ago. And over the next five years, the figure is likely to surpass this record, leading to conditions unobserved in the last 15 million years, according to a new study.

The historical period falls under the Pliocene epoch. During its warmest phase, it had between 380 and 420 parts per million carbon dioxide circulating in the atmosphere, which is close to the current estimate of 415 parts per million. By 2025, the value will exceed those seen 3.3 million years ago, according to researchers from the University of Southampton.

The Pliocene epoch gives us a glimpse of the potential future world, Dr Chalk, the co-author of the study, told MEA WorldWide (MEAWW). "We find that carbon dioxide levels now are likely close to the highest levels found in the mid-Pliocene warm period. This period is associated with sea levels of 10-30m higher than the modern and global temperatures of 3-4 deg C warmer," he added. Dr Elwyn de la Vega, who led the study, said: "Knowledge of carbon dioxide during the geological past is of great interest because it tells us how the climate system, ice sheets, and sea-level previously responded to the elevated CO2 levels." 

To measure the carbon dioxide levels of the Pliocene epoch, the researchers studied fossil remains of plankton that lived before the era took off. Planktons are the primary producers in the aquatic food chain. Because it lived in the surface water, researchers said that the fossil could have gathered records of past atmospheric conditions.

The composition of fossilized zooplankton shells has enabled the reconstruction of past pH and CO2 (University of Southampton)

By studying the shells of the fossil, the team reconstructed the past carbon dioxide conditions. They learned that our current levels mirror that of the Pliocene era.  "Having surpassed Pliocene levels of CO2 by 2025, future levels of CO2 are not likely to have been experienced on Earth at any time for the last 15 million years, since the Middle Miocene Climatic Optimum, a time of even greater warmth than the Pliocene," Dr de la Vega said.

Despite the similar carbon dioxide levels, the Pliocene epoch was warmer and had higher sea levels. The Earth will take some time to adapt and catch up with the rising levels of the greenhouse gas, according to researchers.

 Once Earth adapts to the higher carbon dioxide levels, the temperatures and sea-level rise could resemble the Pliocene epoch. "Of course, this has large ramifications for coastal communities around the globe, expansion, and contraction of different environments as well as the melting of polar ice caps. All these changes will have profound impacts on human settlement and the potential for large scale displacement," Chalk explained.

The study provides details on long-term states of climate. A key limitation of the study is that it does not give us information on the consequences of short-term change in emissions before the Earth adapts to rising carbon dioxide levels. "The rate at which it is changing in the atmosphere now is unprecedented in the last 15 million years," Chalk added.

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