The levels of Carbon dioxide in the atmosphere has broken through a symbolic mark of 400 parts per million (ppm) for the the first time since measurement began in 1958, U.S. government scientists said Friday.
"It's important mainly as a milestone that marks a steady progress of increasing carbon dioxide in the atmosphere," said James Butler of NOAA's Earth System Research Laboratory.
The news has become an important talking point at the U.N. climate change negotiations, with many climate scientists saying that it has now reached a dangerous level.
"Most experts that really study CO2 amounts estimate that we haven't seen that amount of CO2 in our atmosphere in about 3 million years," said J. Marshall Shepherd, climate change expert and professor at the University of Georgia, according to CNN.
Carbon dioxide is considered the most important of the manmade greenhouse gases blamed for raising the temperature on the planet over recent decades.
"The passing of this milestone is a significant reminder of the rapid rate at which - and the extent to which - we have increased the concentration of greenhouse gases in the atmosphere," said Prof Rajendra Pachauri, chair of the Intergovernmental Panel on Climate Change, which serves as science adviser to the world's governments. "At the beginning of industrialization the concentration of CO2 was just 280ppm. We must hope that the world crossing this milestone will bring about awareness of the scientific reality of climate change and how human society should deal with the challenge."
The measurement was made in Mauna Loa, Hawaii, where the National Oceanic and Atmospheric Administration observatory is located. The volcano has long been ground zero for monitoring the worldwide trend on carbon dioxide, or CO2. Devices there sample clean, crisp air that has blown thousands of miles across the Pacific Ocean, producing a record of rising carbon dioxide levels that has been closely tracked for half a century. The station feeds its numbers into a continuous record of the concentration of the gas stretching back to 1958.
The last time such high amounts of greenhouse gas were in the air was several million years ago, when the Arctic was ice-free, savannah spread across the Sahara desert and before modern humans existed. Scientists say the climate back then was also considerably warmer than it is today.
