Rising CO₂ levels are reflected in human blood. Scientists don't know what it means

Humans evolved in an atmosphere containing roughly 200–300 parts per million (ppm) of carbon dioxide (CO₂). Today, that ...
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Earth's CO2 hits highest recorded level in human history - exceeding 430 parts per million

There's now more carbon dioxide (CO2) in the atmosphere than ever before in human history, scientists have revealed. For the first time on record, monthly average CO2 levels exceeded 430 parts per ...
NBC Chicago

Earth's atmosphere hasn't had this much CO2 in millions of years

Earth’s atmosphere now has more carbon dioxide in it than it has in millions — and possibly tens of millions — of years, according to data released Thursday by the National Oceanic and Atmospheric ...