The World Meteorological Organization (WMO) on Monday said the monthly concentrations of carbon dioxide (CO2) in the atmosphere for the first time topped 400 parts per million (ppm) in April throughout the northern hemisphere. According to WMO Global Atmosphere Watch network, all of its monitoring stations in northern hemisphere reported record atmospheric CO2 concentrations during the seasonal maximum. WMO noted all monitoring stations in the Arctic have recorded average monthly CO2 concentrations in spring above 400 ppm since 2012, and the trend has now spread to observing stations at lower latitudes. WMO's global observing stations in Cape Verde, Germany, Ireland, Japan, Spain and Switzerland all reported monthly mean concentrations above 400 ppm in both March and April. WMO Secretary-General Michel Jarraud said the record high of CO2 concentration during April should serve as another wakeup call about the constantly rising levels of greenhouse gases which are driving climate change. He stressed that "If we are to preserve our planet for future generations, we need urgent action to curb new emissions of these heat trapping gases." Statistics from WMO showed the amount of CO2 in the atmosphere reached 393.1 ppm in 2012, or 141 percent of the pre-industrial level of 278 ppm. The amount of CO2 in the atmosphere has increased on average by 2 ppm per year for the past 10 years. Whilst the spring maximum values in the northern hemisphere have already crossed the 400 ppm level, WMO warned that the global annual average CO2 concentration is set to cross this threshold in 2015 or 2016.