Planet-warming carbon dioxide in Earth’s atmosphere — at its highest level in three million years — is poised to lock in dramatic temperature and sea level rises over a timescale of centuries, scientists warned this week.

The last time that CO2 hit 400 parts per million (ppm) Greenland was ice free and trees grew at the edge of Antactica.

It was long thought that today’s greenhouse gas levels were no greater than those 800,000 years ago, during a period of cyclical planetary warming and cooling that would have likely continued but for manmade emissions.

But analyses of ice cores and ocean sediments in the coldest place on Earth have now revealed that 400 ppm was last surpassed three million years ago during the Late Pliocene, when temperatures were several degrees Celsius higher, and oceans at least 15 metres deeper.

At the same time, state-of-the-art climate modelling by experts at the Potsdam Institute for Climate Impact Research (PIK) have correlated directly with the CO2 levels found in these Antarctic samples.

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