McKibben: 400ppm is a grim climate landmark

By John Parnell

The latest data from the Mauna Loa observatory in Hawaii has recorded atmospheric CO2 concentrations of 400 part per million (ppm), a level not sustained for more than 3 million years.

The Keeling Curve data, named after the Scripps Institution of Oceanography’s Dave Keeling, has recorded CO2 levels since 1958 and was widely expected to hit 400ppm this month.

Scientists recommend a level closer to 350ppm in order to limit average temperature rises to less than 2°C. On May 9 it hit 400.03ppm.

Bill McKibben, founder of the 350 campaign group, which takes its name from the target, says some dramatic behaviour change will be required if it is to be any more than a pipedream.

“We’ve known for a long time that we’d pass the 400ppm mark; the trouble is, we’re passing it without any real national or international effort to slow down the production of CO2. So it’s an entirely grim landmark,” said McKibben.

“Before we can get back to 350 we actually have to stop increasing carbon concentrations. That’s a political task; it’s why we’re trying to build a movement strong enough to stand up to the fossil fuel industry.

“Their current business plans – their carbon reserves – take us to 600 or 700ppm, and they’re spending $675bn a year looking for yet more coal and gas and oil,” he added.

The Mauna Loa observatory on Hawaii has recorded data related to atmospheric change since the 1950’s

Writing on his blog, Al Gore said the milestone was an opportunity to redouble efforts to tackle climate change.

“This number is a reminder that for the last 150 years – and especially over the last several decades – we have been recklessly polluting the protective sheath of atmosphere that surrounds the Earth and protects the conditions that have fostered the flourishing of our civilization,” he said.

“We must summon the very best of the human spirit and draw on our courage, our ingenuity, our intellect, and our determination to confront this crisis.”


While the recommendation to pursue 350ppm has come from science, one leading climate scientist is unsure if the current growth can be arrested.

“The system is already adjusting to the change, but there is more to come, much more,” warns Professor Chris Rapley of University College London.

“In my lifetime the figure has increased by 100 units – the same change as during the 100,000 year rhythm over recent ice-age cycles – but to a level not visited by the planet for at least 3 million years,” he said.

Rapley is sceptical as to whether the 350ppm level can be reached through climate action.

“I don’t see how it is possible to do so. There isn’t the means or the interest,” he said adding that on balance, politicians are failing to base their policy on the science.

Writing for RTCC, Johan L. Kuylenstierna, executive director Stockholm Environment Institute (SEI) presented the landmark as an opportunity to increase action.

“We have been in the 390s for a while now, and although 400ppm is certainly worse, the world won’t plunge into chaos in May because we crossed that threshold,” he said.

“The new record is disheartening, but it can also help raise awareness of climate change, and help push mitigation higher up on the political agenda.

“If we use this opportunity, we can stimulate constructive discussions, focusing on solutions that will benefit the climate, the environment and people.”

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