Earth CO2 levels: Have we crossed a point of no return?

Weston Williams, THE CHRISTIAN SCIENCE MONITOR

The annual low for atmospheric concentrations of carbon dioxide has crossed the 400 parts per million threshold, a level not seen for millions of years.

Earth may have passed a significant symbolic threshold as the global climate continues to grow warmer.Usually, September marks a low in the amount of carbon dioxide (CO2) in the atmosphere. This concentration sets the bar over which levels of the greenhouse gas will fluctuate throughout the next year. But this September, CO2 levels are staying high, at around 400 parts per million, and many scientists think that we will not see levels of the greenhouse gas drop below that threshold within our lifetimes.
Earth has been steadily building up CO2 in the atmosphere since the Industrial Revolution, but the 400 ppm landmark is creating a new normal that hasn’t been seen on this planet for millions of years.
“The last time our planet saw 400 ppm carbon dioxide in our atmosphere was about 3.5 million years ago, and global climate was distinctly different than today,” David Black, associate professor in the School of Marine and Atmospheric Sciences at Stony Brook University in New York, tells The Christian Science Monitor in an email.
Read more at: Earth CO2 levels: Have we crossed a point of no return? – CSMonitor.com