Atmospheric CO2 Levels Highest Since 2.9 Million Years Before Modern Humans Emerged
Global CO2 levels rose above 400 parts per million for the first time ever in the modern era in March 2015, marking a significant milestone in the planet's progression toward a warmer future. The measurements were released by the National Oceanic and Atmospheric Administration.
The last time CO2 levels were this high was 3 million years ago during the Pliocene era. There was little ice at the poles then. Ellesmere Island, which is today part of the Canadian tundra, had forests growing on it.
Scientists have long expected global CO2 levels to breach 400 ppm, since levels regionally have been this high for a while. The Arctic hit the threshold in 2012, and the famed Mauna Loa observatory in Hawaii caught up in 2013 (ClimateWire, March 25, 2014).
"This is significant in the sense that it is another milestone for what humankind is doing to the atmosphere," said Pieter Tans, lead scientist of NOAA's Global Greenhouse Gas Reference Network. Humans are raising CO2 levels by 2 ppm every year, a rate that is 100 times greater than witnessed in the past, Tans said.
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