26 May 2014: The World Meteorological Organization (WMO) confirmed that atmospheric carbon dioxide concentrations have crossed a new threshold, with April’s monthly concentration topping 400 parts per million (ppm) throughout the northern hemisphere. While atmospheric carbon dioxide levels reached 400 ppm in April 2012, this record is the first time the monthly average did. The WMO predicts the global annual average carbon dioxide concentration will cross this threshold in 2015 or 2016.

In a statement, WMO Secretary-General Michel Jarraud said “This should serve as yet another wakeup call about the constantly rising levels of greenhouse gases (GHGs) which are driving climate change.” Stressing “time is running out,” Jarraud called for urgent action to curb GHG emissions and preserve the planet for future generations.

Carbon dioxide concentrations are highest during the winter-spring peak when organic material decomposition is higher and there is a lack of biospheric uptake. Concentrations are also higher in the northern hemisphere, which has more sources of anthropogenic carbon dioxide.

All of the WMO’s Global Atmosphere Watch network monitoring stations in the northern hemisphere reported record concentrations. In April, the monthly mean concentration passed 401.3 at Mauna Loa, Hawaii. In 2013, in contrast, this threshold was only passed on a couple of days.

The amount of carbon dioxide in the atmosphere reached 393.1 ppm in 2012 (or 141% of the preindustrial level of 278 ppm) and has increased on average by 2 ppm per year for the past 10 years, according to the WMO’s Greenhouse Gas Bulletin. Since 2012, all Arctic monitoring stations have recorded average monthly concentrations above 400 ppm during the spring months. Observing stations at lower latitudes are also beginning to report monthly mean concentrations above 400 ppm, including stations in Cape Verde, Germany, Ireland, Japan and Switzerland, all of which reported concentrations above 400 ppm in both March and April.

The WMO Global Atmosphere Watch coordinates observations of carbon dioxide and other atmospheric GHGs to ensure standard, comparable measurements around the world. The network covers over 50 countries, with all stations positioned in unpolluted locations. Monthly mean concentrations are calculated on the basis of continuous measurements. Approximately 130 stations measure carbon dioxide globally. [WMO Press Release] [UN Press Release]