New research from the National Oceanic and Atmospheric Administration (NOAA) shows global carbon dioxide concentrations have risen above 400 parts per million for the first time since recordings began.
The unusually high measurements represent the global carbon dioxide levels for March of 2015. Levels of 400 ppm were first reported in the spring of 2012 when all of the observed Arctic sites reached that value. In 2013 the first cross of this threshold was observed.
"It was only a matter of time that we would average 400 parts per million globally..Reaching 400 parts per million as a global average is a significant milestone," said Pieter Tans, lead scientist of NOAA's Global Greenhouse Gas Reference Network. "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 time. Half of that rise has occurred since 1980."
The International Energy Agency reported on March 13 that the growth of global emissions caused by fossil fuel burning stalled in 2014, but stabilizing the emission rate is not believed to be enough to turn the effects of climate change around. The average growth rate of carbon dioxide concentration in the atmosphere between 2012 and 2014 was 2.25 ppm per year, which is the highest that has ever been recorded over three consecutive years. The measurements were based on air samples taken from 40 sites across the globe, mainly on boats in the ocean and from the shores of remote islands.
"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 researchers predict the global average will remain above 400 ppm through the end of May, which is when global carbon dioxide concentrations peak as a result of both natural cycles and emissions.
"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."
