The last time atmospheric carbon dioxide levels were this high, millions of years ago, the planet was very different. For one, humans didn’t exist.
On Wednesday, scientists at the University of California in San Diego confirmedthat April’s monthly average atmospheric carbon dioxide concentration breached 410 parts per million for the first time in our history.
We know a lot about how to track these changes. The Earth’s carbon dioxide levels peak around this time every year for a pretty straightforward reason. There’s more landmass in the northern hemisphere, and plants grow in a seasonal cycle. During the summer, they suck down CO2, during the winter, they let it back out. The measurements were made at Mauna Loa, Hawaii — a site chosen for its pristine location far away from the polluting influence of a major city.
Increasingly though, pollution from the world’s cities is making its way to Mauna Loa — and everywhere else on Earth.
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.
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