Source: http://www.wmo.int
For the first time, monthly concentrations of carbon dioxide (CO2) in the atmosphere topped 400 parts per million (ppm) in April throughout the northern hemisphere. This threshold is of symbolic and scientific significance and reinforces evidence that the burning of fossil fuels and other human activities are responsible for the continuing increase in heat-trapping greenhouse gases warming our planet.
All the northern hemisphere monitoring stations forming the World Meteorological Organization (WMO) Global Atmosphere Watch network reported record atmospheric CO2 concentrations during the seasonal maximum. This occurs early in the northern hemisphere spring before vegetation growth absorbs CO2.
Whilst the spring maximum values in the northern hemisphere have already crossed the 400 ppm level, the global annual average CO2 concentration is set to cross this threshold in 2015 or 2016.