Global carbon dioxide levels set to pass 400ppm milestone

The concentration of carbon in the atmosphere over the next few days is expected to hit record levels

Hawaii's Mauna Loa observatory, where record CO2 increases
 are being documented. Photograph: Richard Vogel/AP

Readings at the US government's Earth Systems Research laboratory in Hawaii, are not expected to reach their 2013 peak until mid May, but were recorded at a daily average of 399.72ppm on 25 April. The weekly average stood at 398.5 on Monday.

Hourly readings above 400ppm have been recorded six times in the last week, and on occasion, at observatories in the high Arctic. But the Mauna Loa station, sited at 3,400m and far away from major pollution sources in the Pacific Ocean, has been monitoring levels for more than 50 years and is considered the gold standard.

"I wish it weren't true but it looks like the world is going to blow through the 400ppm level without losing a beat. At this pace we'll hit 450ppm within a few decades," said Ralph Keeling, a geologist with the Scripps Institution of Oceanography which operates the Hawaiian observatory.

CO2 atmospheric levels have been steadily rising for 200 years, registering around 280ppm at the start of the industrial revolution and 316ppm in 1958 when the Mauna Loa observatory started measurements. The increase in the global burning of fossil fuels is the primary cause of the increase.

The approaching record level comes as countries resumed deadlocked UN climate talks in Bonn. No global agreement to reduce emissions is expected to be reached until 2015.

"The 400ppm threshold is a sobering milestone, and should serve as a wake up call for all of us to support clean energy technology and reduce emissions of greenhouse gases, before it's too late for our children and grandchildren," said Tim Lueker, an oceanographer and carbon cycle researcher with Scripps CO2 Group.

The last time CO2 levels were so high was probably in the Pliocene epoch, between 3.2m and 5m years ago, when Earth's climate was much warmer than today.