8th May 2015
Monthly average CO2 is at 400ppm and rising
Atmospheric CO2 remained above 400 parts per million (ppm) through March 2015, the first time it has been at this level for an entire month, according to the National Oceanic and Atmospheric Administration (NOAA). The current concentration of greenhouse gases is the highest it has been for millions of years.
“It was only a matter of time that we would average 400 parts per million globally,” says Pieter Tans, lead scientist of NOAA’s Global Greenhouse Gas Reference Network. “We first reported 400 ppm when all of our Arctic sites reached that value in the spring of 2012. In 2013, the record at NOAA’s Mauna Loa Observatory first crossed the 400 ppm threshold. Reaching 400 parts per million as a global average is a significant milestone.
“This marks the fact that humans burning fossil fuels have caused global carbon dioxide concentrations to rise more than 120 parts per million since pre-industrial times,” he adds. “Half of that rise has occurred since 1980.”
NOAA bases the global CO2 concentration on air samples taken from 40 sites around the world. NOAA and partner scientists collect air samples in flasks while standing on cargo ship decks, on the shores of remote islands, and other isolated locations. It takes some time after each month's end to compute this global average because samples are shipped for analysis at NOAA’s Earth System Research Laboratory in Boulder, Colorado.
“We choose to sample at these sites because the atmosphere itself serves to average out gas concentrations that are being affected by human and natural forces. At these remote sites, we get a better global average,” said Ed Dlugokencky, the NOAA scientist who manages the global network.
The last time atmospheric levels of carbon dioxide were at 400ppm was during the mid-Pliocene, over 3 million years ago. Back then, our ancestors had brains about as big as those of modern chimps. They had only recently developed stone tools and were roaming the savannahs of Africa while being hunted by sabre-toothed cats. Average global temperatures in the mid-Pliocene were up to 3°C hotter than today, exceeding 10°C in the polar regions, with sea levels around 25m (82ft) higher. Many species of plants and animals were living several hundred kilometres further north of where their nearest relatives exist today.
On a geological timescale, the present rate of change in atmospheric CO2 level is unprecedented. During the ancient past, a rise of 10ppm might have taken 1,000 years or more. Today, human activity is adding that much every five years, as we overwhelm nature's ability to absorb it. On current trends, the world is on track for a doubling of greenhouse gas levels in the second half of this century – potentially causing 4 to 6°C of warming. This would lead to a radically altered planet with grave consequences for humanity.
Dr. James Butler, director of NOAA’s Global Monitoring Division, explains that reversing the global CO2 level would be difficult because of its long lifetime: “Elimination of about 80 percent of fossil fuel emissions would essentially stop the rise in carbon dioxide in the atmosphere – but concentrations of carbon dioxide would not start decreasing until even further reductions are made and then it would only do so slowly.”