Observed Carbon Dioxide Concentrations Reach 400 Parts Per Million Threshold
9 May 2013: Observed concentrations of carbon dioxide in the atmosphere have reached the 400 parts per million (ppm) threshold at several stations of the World Meteorological Organization's (WMO) Global Atmosphere Watch network.
WMO reports that according to the US National Oceanic and Atmospheric Administration (NOAA), on 9 May 2013, the daily mean concentration of carbon dioxide in the atmosphere of Mauna Loa, Hawaii, recorded a reading of 400.03 ppm. Mauna Loa is the oldest atmospheric measurement station in the world, carrying out measurements since 1958, and is seen as benchmark site in the Global Atmosphere Watch. The 400 ppm threshold was first crossed at stations in the Arctic in 2012, and at stations closer to the Equator at the end of April 2013.
Commenting on reaching the 400 parts per million mark, Christiana Figueres, UNFCCC Executive Secretary, called for a greatly stepped-up response to climate change by all parts of society.
The Global Atmosphere Watch coordinates observations of carbon dioxide and other heat-trapping gases, such as methane and nitrous oxide, in the atmosphere to ensure that measurements around the world are standardized. The amount of carbon dioxide in the atmosphere has increased on average by 2 ppm per year for the past ten years. At the current rate of increase, the global annual average carbon dioxide concentration is set to cross the 400 ppm threshold in 2015 or 2016. [WMO Press Release] [Statement by UNFCCC Executive Secretary on Crossing of 400 ppm CO2 Threshold][NOAA Press Release]