The ratio of carbon dioxide in Earth's atmosphere is flirting with 400 parts per million, a level last seen about 2.5 million to 5 million years ago, according to the Scripps Institution of Oceanography at the University of California, San Diego.
The institution this week launched a daily Keeling curve update, showing the saw-toothed upward diagonal of rising carbon dioxide levels since the late 1950s.
Isolated measurements have peaked at above 400 parts per million in the Arctic, but scientists are more alarmed at steady readings from Mauna Loa, Hawaii, far from major pollution sources. Those measurements, considered to be the most reliable indicators of Earth's atmospheric content, could breach the 400 level this month, according to Scripps.
The speed at which Earth's atmosphere has reached that density of carbon dioxide, a known greenhouse gas, has scientists alarmed.
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