Atmospheric CO2 Concentrations Surpass 400 PPM Milestone

Atmospheric concentrations of carbon dioxide reached a daily average above 400 parts per million for the first time in human history.

The milestone hit on May 9, reported NOAA

Manmade CO2 emissions from the burning of fossil fuels continue to rise, bringing greater atmospheric warming and exacerbating the effects of climate change.

Research showed that continued emissions of long-lived greenhouse gases like carbon dioxide will mean "largely irreversible" climate change for 1,000 years even after we curtail emissions.

"The last time we're confident that CO2 was sustained at these levels is more than 10 million years ago, during the middle of the Miocene period," climate scientist Michael Mann told The Huffington Post in an email. "This was a time when global temperatures were substantially warmer than today, and there was very little ice around anywhere on the planet."