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Atmospheric CO2 levels in 2016 hit record high

Smokestacks at a coal power plant. Photo: Charlie Riedel / AP

The average concentration of atmospheric CO2 around the world reached 403.3 parts per million in 2016, up from 400 ppm in 2015, per a report from the UN's World Meteorological Organization. The last time levels of CO2 were this high on Earth was 3 to 5 million years ago — a time when the global "temperature was 2–3°C warmer and sea level was 10–20 meters higher than now."

The big picture, via the WMO: "This record annual increase of 3.3 ppm was partly due to the strong 2015/2016 El Niño, which triggered droughts in tropical regions and reduced the capacity of 'sinks' like forests, vegetation and the oceans to absorb CO2."