Global Warming

Greenhouse Gas Milestone to Be Reached This Month

Greenhouse gas emissions are accelerating even as their effects on climate are becoming more evident.

The amount of carbon dioxide in the Earth’s atmosphere is on the verge of exceeding 400 parts per million (ppm) this month, a concentration of the climate-warming gas not seen on the planet in 3 million years.

That projection is based on observations made at Mauna Loa Observatory, the volcano-top Hawaiian lab where measurements of atmospheric CO2 have been collected since 1958.

Since then, the seasonally fluctuating levels have risen from 316 ppm at an escalating rate.

According to Ralph Keeling, a geochemist at the Scripps Institution of Oceanography, the surpassing of the 400-ppm mark should serve as a warning that despite increased public awareness of the danger posed by global warming, worldwide carbon dioxide emissions show no sign of reversing.

"We are starting to move toward alternate fossil energy — non-conventional fossil fuels like tar sands and so forth," warns Keeling. "And that’s a little troubling because it reflects our willingness to expand and use reserves of fossil fuels that probably ought to stay in the ground if we take this problem seriously."

Exceeding 400 ppm does not correspond to any specific climatological event. However, as politicians, scientists, and activists around the world push for new policies to curb greenhouse gas emissions and mitigate global warming, the new record-breaking figure may increase the sense of urgency for some.

Prior to the mid-18th century, when humans first began burning carbon-based fuels for industrial use, concentration of carbon dioxide is thought to have been stable at approximately 280 ppm.