The monthly global average concentration of carbon dioxide just broke 400 parts per million for the first time since record-keeping of greenhouse gas levels began.
The milestone, reached last month, was announced by the National Oceanic and Atmospheric Administration on Wednesday.
“It was only a matter of time that we would average 400 parts per million globally,” said NOAA scientistPieter Tans in a press release. “We first reported 400 ppm when all of our Arctic sites reached that value in the spring of 2012. In 2013 the record at NOAA’s Mauna Loa Observatory first crossed the 400 ppm threshold. Reaching 400 parts per million as a global average is a significant milestone.”
Crossing the 400 ppm threshold is equal parts disheartening and alarming. Less than a decade ago scientists andenvironmental activists,including Bill McKibben, launched a campaign to convince policy makers that global CO2 concentrations…
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