World Meteorological Organization

The State of Greenhouse Gases in the Atmosphere Using Global Observations through 2012

Supplementary materials to the WMO Greenhouse Gas Bulletin N.9

Overview

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%[4]  of radiative forcing due to LLGHGs (Figure 1).

The WMO Global Atmosphere Watch Programme (http://www.wmo.int/gaw) coordinates systematic observations and analysis of greenhouse gases and other trace species. Sites where greenhouse gases are monitored in the last decade are shown in Figure 2. During 2012, the number of observational stations declined. Measurement data are reported by participating countries and archived and distributed by the World Data Centre for Greenhouse Gases (WDCGG) at the Japan Meteorological Agency.

Table 1. Global annual mean abundances (2012) and trends of key greenhouse gases from the WMO/GAW global greenhouse gas monitoring network. Units are dry-air mole fraction, and uncertainties are 68% confidence limits.

* Assuming a pre-industrial mole fraction of 278 ppm for CO2, 700 ppb for CH4 and 270 ppb for N2O.

The three greenhouse gases shown in the Table 1 are closely linked to anthropogenic activities and they also interact strongly with the biosphere and the oceans. Predicting the evolution of the atmospheric content of greenhouse gases requires an understanding of their many sources, sinks and chemical transformations in the atmosphere.

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).

Implications for climate: Challenges to keep below 2ºC Source: Peters et al. 2013; Global Carbon Project 2012 An emission pathway with a “likely chance” to keep the temperature increase below 2ºC has significant challenges Role of the greenhouse gases in total radiative forcing (Working Group I Contribution to the IPCC Fifth Assessment Report Climate Change 2013: The Physical Science Basis, Figure SPM.5)

Carbon Dioxide (CO2)

Carbon dioxide is the single most important anthropogenic greenhouse gas in the atmosphere, contributing ~64%[4] 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[1] in 2011 according to  http://www.globalcarbonproject.org), deforestation and other land-use change (0.9±0.5 PgC[1] 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. The portion of CO2 emitted by fossil fuel combustion that remains in the atmosphere (airborne fraction), varies interannually due to high natural variability of CO2 sinks (Levin, 2012) without a confirmed global trend.

Figure 3. Globally averaged CO2 mole fraction (a) and its growth rate (b) from 1984 to 2012. Annually averaged growth rates are shown as columns in (b).

 

Importance of the CO2 sinks: Cover story of the GHG Bulletin No.8 (2012)

The “other” CO2 problem – Ocean acidification Profound changes in seawater chemistry are underway as the ocean takes up about one fourth of the anthropogenic CO2 emitted to the atmosphere year-on-year. This phenomenon, known as ocean acidification, has emerged as a key issue of global concern in the last fifteen years. Some facts about ocean acidifications can be found in “20 Facts about ocean acidification”.The Ocean Acidification International Coordination Centre (OA-ICC) works to promote, facilitate and communicate global activities on ocean acidification.  At the “Surface Ocean CO2 Variability and Vulnerability” (SOCOVV) workshop at UNESCO, Paris in April 2007, participants agreed to establish a global surface CO2 data set that would bring together, in a common format, all publicly available fCO2 data for the surface oceans. This work allowed to map the distribution of fCO2 in Surface Ocean CO2 Atlas (SOCAT, www.socat.info/about.html), which includes:  - a 2nd level quality controlled global surface ocean fCO2  data set following agreed procedures and regional review, - and a gridded SOCAT product of monthly surface water fCO2 means on a 1° x 1° grid with no temporal or spatial interpolation. EXAMPLE: SOCAT product for January

 

Methane (CH4)

Methane contributes ~18%[4] 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).

(Global Carbon Project 2013; Figure based on Kirschke et al. 2013, Nature Geoscience)

 

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.

Figure 4. Globally averaged CH4 mole fraction (a) and its growth rate (b) from 1984 to 2012. Annually averaged growth rates are shown as columns in (b).

Attribution of methane abundance changes: cover story of this Bulletin.

Nitrous Oxide (N2O)

Figure 5. Globally averaged N2O mole fraction (a) and its growth rate (b) from 1980 to 2012. Annually averaged growth rates are shown as columns in (b).

 

Other greenhouse gases

 This bulletin primarily addresses LLGHGs. Relatively short-lived tropospheric ozone has a radiative forcing comparable to that of the halocarbons. Many other pollutants, such as carbon monoxide, nitrogen oxides and volatile organic compounds, although not referred to as greenhouse gases, have small direct or indirect effects on radiative forcing. Aerosols (suspended particulate matter), too, are short-lived substances that alter the radiation budget. All gases mentioned herein, as well as aerosols, are monitored by the GAW Programme, with support from WMO Member countries and contributing networks.

Acknowledgements and links

Fifty WMO member countries have contributed CO2 data to the GAW WDCGG. Approximately 47% of the measurement records submitted to WDCGG are obtained at sites of the NOAA ESRL cooperative air-sampling network.  For other networks and stations see GAW Report No. 206 (available at http://www.wmo.int/gaw). The Advanced Global Atmospheric Gases Experiment (AGAGE) is contributing observations to this bulletin. Furthermore, the GAW monitoring stations contributing data to this bulletin, shown in Figure 2, are included in the list of contributors on the WDCGG web page (http://ds.data.jma.go.jp/gmd/wdcgg/). They are also described in the GAW Station Information System, GAWSIS (http://gaw.empa.ch/gawsis) supported by MeteoSwiss, Switzerland.

References

Bergamaschi, P.,  Houweling,S., Segers, A., et al.: Atmospheric CH4 in the first decade of the 21st century: Inverse modeling analysis using SCIAMACHY satellite retrievals and NOAA surface measurements, J. Geophys. Res., 118, 7350–7369, 2013, doi:10.1002/jgrd.50480

Conway, T. J., Tans, P. P. , Waterman, L. S., Thoning, K. W., Kitzis, D. R., Masarie, K. A. and Zhang, N. Evidence for interannual variability of the carbon cycle from the National Oceanic and Atmospheric Administration/Climate Monitoring and Diagnostics Laboratory global air sampling network, J. Geophys. Res., 99, 22831-22855, 1994.

Levin, I., Earth science: The balance of the carbon budget, Nature, 488, 35–36, 2012, doi:10.1038/488035a

WMO, 2009: Technical Report of Global Analysis Method for Major Greenhouse Gases by the World Data Centre for Greenhouse Gases (Y. Tsutsumi, K. Mori, T. Hirahara, M. Ikegami and T.J. Conway). GAW Report No. 184 (WMO/TD No. 1473), Geneva, 29 pp.

Notes:

Terms used in this Bulletin are explained in the glossary.