Global CO2 Levels Approach Worrisome Milestone

Concentrations of greenhouse gases in Earth's atmosphere will surpass 400 parts per million in the next month. Nations could have a hard time keeping global warming in check at that level

By Richard Monastersky and Nature magazine

Continuing reliance on coal, which fuels this power plant in Brazil, is driving carbon dioxide levels in the atmosphere ever higher. Image: Flickr/guilherme

Near the moonscape summit of the Mauna Loa volcano in Hawaii, an infrared analyzer will soon make history. Sometime in the next month, it is expected to record a daily concentration of carbon dioxide in the atmosphere of more than 400 parts per million (p.p.m.), a value not reached at this key surveillance point for a few million years.

There will be no balloons or noisemakers to celebrate the event. Researchers who monitor greenhouse gases will regard it more as a disturbing marker of humanity?s power to alter the chemistry of the atmosphere and by extension, the climate of the planet. At 400?p.p.m., nations will have a difficult time keeping global warming in check, says Corinne Le Qu?r?, a climate researcher at the University of East Anglia in Norwich, UK, who says that the impact ?is getting very dangerously close to reaching the 2??C target that governments around the world have pledged not to exceed?.

It will be a while, perhaps a few years, before the global CO₂ concentration averaged over an entire year, passes 400 p.p.m.. But topping that value at Mauna Loa is significant because researchers have been monitoring the gas there since 1958, longer than any other spot. ?It?s a time to take stock of where we are and where we?re going,? says Ralph Keeling, a geochemist at the Scripps Institution of Oceanography in La Jolla, California, who oversees that center?s CO₂ monitoring efforts on Mauna Loa. That gas record, known as the Keeling curve, was started by his father, Charles Keeling.

Image: Courtesy of Scripps Inst. Oceanography/UC San Diego

When monitoring started, the CO₂ level stood at 316?p.p.m., not much higher than the 280?p.p.m. that characterized conditions before the industrial revolution. But since the Hawaiian measurements began, the values have followed an upward slope that shows no sign of leveling off (see ?On the rise?). Emissions of other greenhouse gases are also increasing, pushing the total equivalent concentration of CO₂ in the atmosphere to around 478?p.p.m. in April, according to Ronald Prinn, an atmospheric scientist at the Massachusetts Institute of Technology in Cambridge.

Data compiled by Le Qu?r? and other members of the Global Carbon Project suggest that humans contributed around 10.4?billion tons of carbon into the atmosphere in 2011. About half of that is taken up each year by carbon ?sinks? such as the ocean and vegetation on land; the rest remains in the atmosphere and raises the global concentration of CO₂.

??The real question now is: how will the sinks behave in the future?? says Gregg Marland, an environmental scientist at Appalachian State University in Boone, North Carolina, who helps to compile the emissions data.

The sinks have grown substantially since Keeling began his measurements, when carbon emissions totalled about 2.5 billion tons a year. But climate models suggest that the land and ocean will not keep pace for long.

?At some point the planet can?t keep doing us a favor, particularly the terrestrial biosphere,? says Jim White, a biogeochemist at the University of Colorado Boulder. As the sinks slow down and more emitted CO₂ stays in the atmosphere, levels will rise even faster.

Source: http://rss.sciam.com/click.phdo?i=113e6ed0d2d500a744eb94b05b6c5ec5

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