The amount of carbon dioxide in the atmosphere surpassed a threshold not seen for 3 million years, exceeding 400 parts per million (ppm) for the first time since researchers began tracking the data.
The main greenhouse gas blamed for global warming averaged 400.03ppm at the United States National Oceanic and Atmospheric Administration’s (NOAA) Mauna Loa monitoring station in Hawaii on May 9, the agency said.
The level is considered a landmark by scientists and environmentalists, who say carbon emissions caused by burning fossil fuels are warming the planet and must be reined in before they cause irreversible changes to weather, sea levels and Arctic ice cover.
NOAA’s data stretches back to 1958.
“We are in the process of creating a prehistoric climate that humans have no evolutionary experience of,” Bob Ward, policy director at the Grantham Research Institute on Climate Change and the Environment at the London School of Economics, said in a telephone interview with Bloomberg newsagency.
The last time CO2 levels were this high was at least three million years ago, he said.
Then, “temperatures were two to three degrees Celsius higher than pre-industrial times.
“As a result the polar ice caps were much smaller, and sea levels were about 20 metres higher than today.”
The atmospheric reading comes three weeks after the European Parliament rejected a plan to shore up prices in the European Union Emissions Trading System (ETS), the world’s biggest effort to control greenhouse-gas pollution.
The system attaches a cost to CO2 released by burning fossil fuels, giving manufacturers and utilities an incentive to reduce emissions.
Australia’s carbon trading market will be linked to the EU ETS in 2015.
Carbon permits traded on the EU ETS are currently about €3.38 a tonne.
Bloomberg quotes analysts such as Professor Sir David King, former chief science adviser to the British government, as saying industry will not eliminate carbon for less than €100 a tonne.
The price has fallen almost 90 per cent since peaking at about €31 in 2006.
Carbon dioxide can stay in the atmosphere for as much as a century, so levels now may cause warming for decades.
The concentration has now increased by more than 40 per cent from the pre-industrial mark of 280ppm.
The Mauna Loa data is important because it represents the longest set of continuous measurements of atmospheric concentrations of carbon dioxide.
Dr Charles David Keeling, a geochemist at the Scripps Institution of Oceanography, began taking readings there in 1958.
Dr Keeling’s measurements provided the first physical evidence of the steady rise in CO2 in the atmosphere as a result of burning fossil fuels, confirming part of Swedish chemist Dr Svante August Arrhenius’s theory from 1896 that burning fossil fuels may cause global warming.
The United Nations in 2007 said stabilising the gas at 400ppm to 440ppm may lead to a temperature gain of as much as 2.8 degrees Celsius.
That’s at odds with the goal set out by climate treaty negotiators from more than 190 nations, who have agreed to shoot for limiting the temperature increase to two degrees Celsius.
The global average has already risen by about 0.8 of a degree since pre-industrial times.
“We are heading in the wrong direction in terms of dealing with climate change,” David Nussbaum, chief executive officer of the environmental group WWF’s British arm, said in an e-mailed statement.
“There is limited time for governments to achieve the goal they have set themselves for agreeing a global deal that effectively tackles climate change.”
Negotiators at the UN talks are working toward agreeing on a global climate treaty in 2015 that would come into force from 2020.
They’ll meet in Warsaw in November to lay the groundwork for those discussions.
The surfeit of greenhouse gases in the atmosphere already threatens the 2-degree target.
At best, pledges by countries from the US and China to the Maldives will cut predicted emissions in 2020 to 52 gigatons from 58 gigatons, the UN Environment Program said in November.
It said the level consistent with two degrees of warming is 44 gigatons.
The UN’s 2007 report also said that atmospheric CO2 in the range of 400 to 440ppm could lead to sea level rise of as much as 1.7 meters.
That would threaten coastal cities from New York to London an
