Humans didn’t exist the last time there was this much CO2 in the air

Thanks largely to our burning of fossil fuels, the average carbon dioxide concentration of the Earth’s atmosphere surged past 410 parts per million in April 2018. It has been a long time since the planet experienced such CO2 levels. How long? It depends on who you ask. Bloomberg says it has been at least a million years. Scientific American says 23 million years ago, at the end of the Oligocene.

This isn’t an example of bad reporting—even scientists argue about this. NASA climate scientist Carmen Boening says we last saw this concentration during the Pliocene (between 2.5 million and 5.3 million years ago). On the very same page, her colleague Charles Miller says 400 ppm is “maybe higher than any time in the last 25 million years.”

On Wednesday, scientists at the University of California in San Diego confirmed that April’s monthly average atmospheric carbon dioxide concentration breached 410 parts per million for the first time in our history.
In little more than a century of frenzied fossil-fuel burning, we humans have altered our planet’s atmosphere at a rate dozens of times faster than natural climate change. Carbon dioxide is now more than 100 ppm higher than any direct measurements from Antarctic ice cores over the past 800,000 years, and probably significantly higher than anything the planet has experienced for at least 15 million years. That includes eras when Earth was largely ice-free.

Not only are carbon dioxide levels rising each year, they are accelerating. Carbon dioxide is climbing at twice the pace it was 50 years ago. Even the increases are increasing.

That’s happening for several reasons, most important of which is that we’re still burning a larger amount of fossil fuels each year. Last year, humanity emitted the highest level of greenhouse gas emissions in history — even after factoring in the expansion of renewable energy. At the same time, the world’s most important carbon sinks — our forests — are dying, and therefore losing their ability to pull carbon dioxide out of the air and store it safely in the soil. The combination of these effects means we are losing ground, and fast.

Without a bold shift in our actions, in 30 years atmospheric carbon dioxide will return back to levels last reached just after the extinction of the dinosaurs, more than 50 million years ago. At that point, it might be too late to prevent permanent, dangerous feedback loops from kicking in.

This is the biggest problem humanity has ever faced, and we’ve barely even begun to address it effectively. On our current pace, factoring in current climate policies of every nation on Earth, the best independent analyses show that we are on course for warming of about 3.4 degrees Celsius above pre-industrial levels, enough to extinguish entire ecosystems and destabilize human civilization.

Climate change demands the urgent attention and cooperation of every government around the world. But even though most countries have acknowledged the danger, the ability to limit our emissions eludes us. After 23 years of United Nations summits on climate change, the time has come for radical thinking and radical action — a social movement with the power to demand a better future.

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