A major climate landmark has been crossed – for the first time in 4 million years

Carbon dioxide levels in the Antarctic just hit 400 parts per million (ppm) – making the polar region the final place on Earth to cross this climate threshold.

The South Pole Observatory breached 400 ppm for the first time on 23rd May, according to the National Oceanic and Atmospheric Administration (NOAA). The organization says this is the first time in 4 million years this level has been reached.

“The far southern hemisphere was the last place on Earth where CO2 had not yet reached this mark,” explained Pieter Tans, lead scientist at NOAA’s Global Greenhouse Gas Reference Network. “Global CO2 levels will not return to values below 400 ppm in our lifetimes, and almost certainly for much longer.”

The rise of CO2 levels

The remote location of the Antarctic observatory means it was the last place on Earth to register a 400ppm reading. As this chart from the NOAA shows, levels have been increasing year on year. Indeed, since observations began in 1958, there has been an increase every year in the global yearly average.

2015 was also the fourth consecutive year that the NOAA have recorded a rise of above 2ppm – with the global average reaching 399ppm last year, it looks set to be over 400ppm this year.

“Since emissions from fossil fuel burning have been at a record high during the last several years, the rate of CO2 increase has also been at a record high,” said Tans. “We know some of it will remain in the atmosphere for thousands of years.”

The global flow of carbon dioxide

Crossing the 400ppm threshold is a symbolic milestone, and a further reminder of our impact on Earth. A major driver of global warming, increasing carbon dioxide has significant implications for life on our home planet.

It’s been three years since the Mauna Loa Observatory in Hawaii first recorded a level above 400ppm. Since then other stations have slowly also crossed the threshold.

As Climate Central explained, this is because “there’s a lag in how carbon dioxide moves around the atmosphere.”

Most of the world’s CO2 originates in the Northern Hemisphere, where the population is concentrated. As the graphic above shows, this then circulates around the world.

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