GHG Concentrations Climbed to New Highs in 2012: WMO

Atmospheric greenhouse gases reached new record levels

Atmospheric concentrations of major greenhouse gases responsible for climate change climbed to new records in 2012, according to WMO Greenhouse Gas Bulletin (No. 9: November 2013) released by the World Meteorological Organisation (WMO).

Levels of CO₂, the primary greenhouse gas produced by human activities, grew by 2.2 ppm, higher the average of 2.02 ppm over the past decade. At 393.1 parts per million (ppm), the 2012 CO₂ concentrations were 41 percent above the pre-industrial level.

The latest analysis of observations from the WMO Global Atmosphere Watch (GAW) Programme shows that the globally averaged mole fractions of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) reached new highs in 2012, with CO₂ at 393.1±0.1 ppm, CH₄ at 1819±1 ppb and N₂O at 325.1±0.1 ppb. These values constitute, respectively, 141%, 260% and 120% of pre-industrial (before 1750) levels. The atmospheric increase of CO₂ from 2011 to 2012 is higher than the average growth rate over the past 10 years. For N₂O the increase from 2011 to 2012 is smaller than the one observed from 2010 to 2011 but larger than the average growth rate over the past 10 years. Atmospheric CH₄ continued to increase at a rate similar to the one observed over the past 4 years. The National Oceanic and Atmospheric Administration (NOAA) Annual Greenhouse Gas Index shows that from 1990 to 2012 radiative forcing by long-lived greenhouse gases increased by 32%, with CO₂ accounting for about 80% of this increase.

This ninth WMO/GAW Annual GHG Bulletin reports atmospheric abundances and rates of change of the most
important long-lived greenhouse gases (LLGHGs) – carbon dioxide, methane, nitrous oxide – and provides a summary of the contributions of the other gases. These three together with CFC-12 and CFC-11 account for approximately 96% of radiative forcing due to LLGHGs.

The NOAA Annual Greenhouse Gas Index (AGGI) in 2012 was 1.32, representing a 32% increase in total radiative forcing (relative to 1750) by all LLGHGs since 1990 and a 1.2% increase from 2011 to 2012 (Figure 1). The total radiative forcing by all LLGHGs in 2012 corresponds to a CO₂-equivalent mole fraction of 475.6 ppm (http://www.esrl.noaa.gov/gmd/aggi).

 Carbon dioxide (CO2) is the single most important anthropogenic GHG in the atmosphere

Carbon dioxide is the single most important anthropogenic greenhouse gas in the atmosphere, contributing ~64%  to radiative forcing by LLGHGs. It is responsible for ~84% of the increase in radiative forcing over the past decade and ~82% over the past five years. The pre-industrial level of ~278 ppm represented a balance of fluxes between the atmosphere, the oceans and the biosphere. Atmospheric CO₂ reached 141% of the pre-industrial level in 2012, primarily because of emissions from combustion of fossil fuels (fossil fuel CO₂ emissions 9.5±0.5 PgC in 2011, according to http://www.globalcarbonproject.org), deforestation and other land-use change (0.9±0.5 PgC in 2011). The average increase in atmospheric CO₂ from pre-industrial time corresponds to ~55% of the CO₂ emitted by fossil fuel combustion with the remaining ~45% removed by the oceans and the terrestrial biosphere.

CO₂ Global Average

The globally averaged CO2 mole fraction in 2012 was 393.1±0.1 ppm. The mean annual increase from 2011 to 2012, 2.2 ppm, is greater than the increase from 2010 to 2011, the average growth rate for the 1990s (~1.5 ppm/yr) and the average growth rate for the past decade (~2.0 ppm/yr).

Global average abundances of the major, well-mixed, long-lived greenhouse gases – carbon dioxide, methane, nitrous oxide, CFC-12 and CFC-11 – from the NOAA global air sampling network are plotted since the beginning of 1979. These gases account for about 96% of the direct radiative forcing by long-lived greenhouse gases since 1750. The remaining 4% is contributed by an assortment of 15 minor halogenated gases including HCFC-22 and HFC-134a. Source: ESRL/NOAA

Methane (CH4) – THe Second Major Contributor

Methane contributes ~18% to radiative forcing by LLGHGs. Approximately 40% of methane is emitted into the atmosphere by natural sources (e.g., wetlands and termites), and about 60% comes from anthropogenic sources (e.g., ruminants, rice agriculture, fossil fuel exploitation, landfills and biomass burning). Atmospheric CH₄ reached 260% of the pre-industrial level (~700 ppb) due to increased emissions from anthropogenic sources. Globally averaged CH₄ reached a new high of 1819 ± 1 ppb in 2012, an increase of 6 ppb with respect to the previous year (Figure 4). The growth rate of CH₄ decreased from ~13 ppb/yr during the early 1980s to near zero during 1999-2006. Since 2007, atmospheric CH₄ has been increasing again due to increased emissions in the tropical and mid-latitude
Northern Hemisphere. The attribution of this increase to anthropogenic and natural sources is difficult because the current network is insufficient to characterize emissions by region and source process.

Nitrous oxide (N₂O )

Nitrous oxide contributes ~6% to radiative forcing by LLGHGs. It is the third most important contributor to the combined forcing. N₂O is emitted into the atmosphere from both natural (about 60%) and anthropogenic sources (approximately 40%), including oceans, soil, biomass burning, fertilizer use, and various industrial processes. The globally averaged N₂O mole fraction in 2012 reached 325.1 ±0.1 ppb, which is 0.9 ppb above the previous year and 120% of the pre-industrial level (270 ppb). The annual increase from 2011 to 2012 is greater than the mean growth rate over the past 10 years (0.80 ppb/yr).

Radiative forcing, relative to 1750, of all the long-lived greenhouse gases. The NOAA Annual Greenhouse Gas Index (AGGI), which is indexed to 1 for the year 1990, is shown on the right axis.  Of the five long-lived greenhouse gases that contribute 96% to radiative climate forcing, CO₂ and N₂O are the only ones that continue to increase at a regular rate. Radiative forcing from CH₄ increased from 2007 to 2012 after remaining nearly constant from 1999 to 2006. While the radiative forcing of the long-lived, well-mixed greenhouse gases increased 32% from 1990 to 2012 (by ~0.69 watts m^-2), CO₂ has accounted for nearly 80% of this increase (~0.55 watts m^-2). Source: ESRL/NOAA

Recent Global CO₂

• August 2013:     393.11 ppm
• August 2012:     389.82 ppm

Up-to-date weekly average CO₂ at Mauna Loa

• Week beginning on October 27, 2013:     394.20 ppm
• Weekly value from 1 year ago:     391.32 ppm
• Weekly value from 10 years ago:     373.39 ppm

Related Links

• Weekly Average CO2 at Mauna Loa Tops 400ppm June 4, 2013
• CO2 Tops 400ppm at Mauna Loa as Forecast May 11, 2013
• Sudden Surges in Atmospheric CO2: FIRE-EARTH Forecast July 23, 2013
• 400 PPM April 3, 2013