7 May 2015: Atmospheric CO2 concentrations reached a record global average in March 2015, underscoring the importance of reaching an effective and universal climate agreement in Paris in December 2015. According to the US National Oceanic and Atmospheric Administration (NOAA), monthly global average CO2 concentrations surpassed 400 parts per million (ppm) in March 2015 for the first time since the administration began tracking atmospheric CO2.

While the 400 ppm threshold was already passed at NOAA’s Mauna Loa Observatory in 2013, this is the first time that the global average crossed this threshold. The March figures have only now become available due to the time necessary for samples to be collected and analyzed. NOAA bases the CO2 concentration on air samples taken from 40 global sites, with NOAA and partner scientists collecting air samples in flasks while standing on cargo ship decks, on the shores of remote islands and elsewhere around the world. Samples are then shipped Boulder, Colorado, for analysis at NOAA’s Earth System Research Laboratory.

According to the Intergovernmental Panel on Climate Change (IPCC), approximately 80% of known fossil fuel reserves would need to stay in the ground atmospheric CO2 concentrations to remain below 450 ppm, which would lead to a 50% chance of limiting temperature to below 2°C.

Pieter Tans, NOAA’s Global Greenhouse Gas Reference Network, said 400 ppm was first reported when all of NOAA’s Arctic sites reached that value in the spring of 2012, adding that burning fossil fuels has caused global CO2 concentrations to increase by more than 120 ppm since pre-industrial times.

The International Energy Agency (IEA) reported that emissions growth from burning fossil fuels stalled in 2014, remaining at 2013 levels. However, stabilizing the rate of emissions is not enough to avert climate change. James Butler, NOAA’s Global Monitoring Division, highlighted difficulties with reversing increases of greenhouse gases (GHGs), noting that eliminating approximately 80% of emissions would halt the rise in atmospheric CO2, but that CO2 concentrations would not begin decreasing until further reductions are made and even then, they would decrease slowly. NOAA scientists expect the global average to remain above 400 ppm through May, when CO2 concentrations peak due to natural cycles combined with rising GHGs.

Responding to this finding, UNFCCC spokesperson Nick Nuttall said the Paris agreement and related decisions must constitute a long-term development plan that provides the policies, pathways and finance for triggering a peaking of global emissions in ten years. He said a deep decarbonization of the global economy should follow by the second half of the century. [UNFCCC Press Release] [NOAA Press Release] [NOAA Website on Trends in Atmospheric CO2 Concentrations]