Carbon Dioxide at Highest Level in Human History, Raises Concerns

For the first time in human history, Carbon dioxide levels in the atmosphere have broken through a symbolic mark of 400 parts per million (ppm), U.S. government scientists said Friday.

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.

"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 amount of carbon dioxide varies daily somewhat and has cycled historically in accordance with changes in the Earth's orbit, a phenomenon known as Milankovitch cycles. But the exponential rise in carbon dioxide levels since the Industrial Revolution is far out of the ordinary, experts say.