Average global levels of carbon dioxide stayed above 400 parts per million, or ppm, through all of March 2015 -- the first time that has happened for an entire month since record keeping first began, according to data released this week by the National Oceanic and Atmospheric Administration (NOAA).
Scientists with NOAA's Earth System Research Laboratory have called the news a "significant milestone" in the growing scourge of man-made climate change.
“This marks the fact that humans burning fossil fuels have caused global carbon dioxide concentrations to rise more than 120ppm since pre-industrial times,” Pieter Tans, lead scientist of NOAA's greenhouse gas network, told The Guardian on Wednesday. “Half of that rise has occurred since 1980.”
In May 2013, atmospheric levels of CO2 topped a daily average of 400 ppm for the first time. Some parts of the planet were consistently above the mark for most of last summer, and the entirety of the Northern Hemisphere hit the threshold in May 2014.
Average greenhouse gas levels haven't been this high since between 800,000 and 15 million years ago, according to Climate Central.
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