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May 13, 2013
Three Million Years Later, 400 Parts per Million of CO2 in Atmosphere
    by Robert Kropp

Daily concentrations of carbon dioxide in the atmosphere pass the 400 parts per million threshold, foretelling severe effects from climate change if a long-overdue reversal of the trend does not occur.

The National Oceanic and Atmospheric Administration (NOAA) reporte d last week that for the first time, the daily mean concentration of carbon dioxide in the atmosphere surpassed 400 parts per million (ppm) at its measurement station in Mauna Loa, Hawaii.

The levels of CO2 measured at Mauna Loa have not been experienced on Earth in at least three million years.

Climate scientists have been warning for several years that atmospheric concentrations of CO2 will have to be reduced to 350 ppm if the catastrophic effects of climate change are to be averted. However, as former NASA scientist James Hanson and co-authors warned in 2008, "If the present overshoot of this target CO2 is not brief, there is a possibility of seeding irreversible catastrophic effects."

One such irreversible effect will be the melting of the Arctic ice sheet. The UK-based Arctic Methane Emergency Group (AMEG) warned in 2012 that evidence "strongly suggests that a final collapse in the sea ice is underway and closely following an exponential downward trend in sea ice volume." In fact, an ice-free may occur as soon as the summer of 2015, scientists now say. Methane is many times more powerful a driver of climate change than CO2, and if the release of methane from warming sea beds increases, the "irreversible catastrophic effects" referred to by Hanson are almost certain to occur.

AMEG considers the release of Arctic methane into the atmosphere to constitute such a planetary emergency that the organization is advocating for some form of geoengineering to delay its occurrence.

Also, with global greenhouse gas (GHG) emissions continuing to set annual records, the day is fast approaching when the concentration of CO2 in the atmosphere will reach 450 ppm, a level at which global temperatures will have increased by two degrees Celsius. There is general agreement among climate scientists that a temperature increase of two degrees represents the point of no return, after which the disastrous effects of climate change are likely to multiply.

Especially sobering about the Mauna Loa measurements is that the milestone has been reached in such a short period of time. The concentration of CO2 in the atmosphere "has increased every year since scientists started making measurements on the slopes of the Mauna Loa volcano more than five decades ago," NOAA scientists reported. "The rate of increase has accelerated since the measurements started, from about 0.7 ppm per year in the late 1950s to 2.1 ppm per year during the last 10 years."

"Climate changes forced by CO2 depend primarily on cumulative emissions," NOAA continued, "making it progressively more and more difficult to avoid further substantial climate change."

Former Vice-President Al Gore wrote of the findings, "We have been recklessly polluting the protective sheath of atmosphere that surrounds the Earth and protects the conditions that have fostered the flourishing of our civilization…every single day we pour an additional 90 million tons of global warming pollution into the sky as if it were an open sewer."

The environmental advocacy organization has established a website to emphasize the significance of the 400 ppm milestone. "It's been millions of years since there's been this much carbon in the atmosphere," 350,org co-founder Bill McKibben stated. "The only question now is whether the relentless rise in carbon can be matched by a relentless rise in the activism necessary to stop it."


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