This seasonal maximum for CO2 concentrations occurs early in the Northern hemisphere spring before vegetation growth absorbs CO2, levels are lower for the rest of the year. At the current rate of increase, the global annual average CO2 concentration is set to cross the 400 ppm threshold in 2015 or 2016.
“The 400 parts per million threshold is of great symbolic importance,” said WMO Secretary-General Michel Jarraud. “It should serve as yet another wakeup call about the constantly rising levels of greenhouse gases which are driving climate change and acidifying our oceans. If we are to preserve our planet for future generations, we need urgent action to curb new emissions of these heat trapping gases,” he said.
CO2 remains in the atmosphere for thousands of years, trapping heat and causing Earth to warm further. Its lifespan in the oceans is even longer. It is the single most important greenhouse gas emitted by human activities. It is responsible for 85% of the increase in radiative forcing – the warming effect on our climate - over the past decade. Between 1990 and 2012 there was a 32% increase in radiative forcing because of greenhouse gases. Increasing radiative forcing is calculated relative to the pre-industrial level of key greenhouse gases.
The amount of CO2 in the atmosphere has increased on average by 2 ppm per year for the past 10 years.