© Climate Central

5/16/2013 9:59:20 PM

Carbon Dioxide Surpasses 400 Parts Per Million

We're reaching new carbon dioxide (CO2) milestones, but there's no reason to celebrate. On May 9, concentration of CO2 in the atmosphere of Mauna Loa, Hawaii, surpassed 400 parts per million (ppm) for the first time since measurements began in 1958.

Mauna Loa is the primary global benchmark site for monitoring the increase of this potent heat-trapping gas.

"That increase is not a surprise to scientists," said NOAA senior scientist Pieter Tans, with the Global Monitoring Division of NOAA's Earth System Research Laboratory in Boulder, Colorado. "The evidence is conclusive that the strong growth of global CO2 emissions from the burning of coal, oil, and natural gas is driving the acceleration."

CO2 is the most significant greenhouse gas contributing to global warming. In 2011, CO2 accounted for about 84% of all U.S. greenhouse gas emissions from human activities, primarily from the burning of fossil fuels. These human activities are altering the carbon cycle—both by adding more CO2 to the atmosphere and by deforestation that influences the ability of natural sinks, like forests, to remove CO2 from the atmosphere.

"We're reaching dangerous levels of greenhouse gas concentrations that are already affecting polar bear habitat," Dr. Steven C. Amstrup, our chief scientist, said. "Our research has confirmed that, other things being equal, polar bears are likely to persist in relevant numbers over significant portions of the Arctic if we can keep CO2 at or below 450 parts per million. But the relentless climb in CO2 means if we are to stay below that value, the time to act is now. If we don't, we'll no longer be worried about polar bears—but life as we know it on Earth."

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