Why the 400ppm CO2 Milestone is so Important

Charles David Keeling began recording CO2 levels at Hawaii’s Mauna Loa Observatory in 1958, back when concentrations hovered at around 315 parts per million. Five decades later and that number has soared to 400ppm and his son told Yale Environment 360 we’re unlikely to stop it from rising any time soon. Director of the Scripps CO2 Program in California, which is designed to make climate change science accessible to the lay person, Ralph Keeling said that the number 400 is a milestone mostly because it’s a nice round number that people can grasp.

“So this is really a moment for human awareness,” he said, “just like passing a 50th birthday.”

“This is a point to think about where we are in the course of the rise of carbon dioxide. It feels a little bit like we’re moving into another era, in that somehow between 350 and 400 parts per million feels like a certain kind of range of CO2, and now we’re moving into a different range.”

He said that in order to keep levels from surpassing 400ppm, we would have to reduce fossil fuel consumption by up to 60 percent, right now, something that is essentially not going to happen.

Not only would it be virtually impossible to get the whole planet behind the idea, it would be financially crippling.

As a result, we are on track to reach 450ppm in the next 20 to 25 years and further exponential escalations thereafter.

Keeling estimates that the earth’s CO2 concentration last reached 400ppm between two and four million years ago during the mid-Pliocene era.

Combining methane and other heat-trapping gases with CO2 emissions, Keeling told Yale Environment 360 that we are probably going to double pre-industrial levels of greenhouse gas concentrations by the middle of this century.

Reluctant to present himself as a problem solver, Keeling suggests that adopting more fossil fuels and eliminating unrealistically low energy prices might take us one step closer to averting the worst.

:: The Guardian

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