ALBERT

Description: The global burden of atmospheric methane has been increasing over the past decade but the causes are not well understood. National inventory estimates from the US Environmental Protection Agency (EPA) indicate no significant trend in US anthropogenic methane emissions from 2002 to present. Here we use satellite retrievals and surface observations of atmospheric methane to suggest that US methane emissions have increased by more than 30% over the 2002–2014 period. The trend is largest in the central part of the country but we cannot readily attribute it to any specific source type. This large increase in US methane emissions could account for 30–60% of the global growth of atmospheric methane seen in the past decade.

Description: We present methane (CH 4 ) emissions for East Asia from a Bayesian inversion of CH 4 mole fraction and stable isotope (δ 13 C-CH 4 ) measurements. Emissions were estimated at monthly resolution from 2000 to 2011. A posteriori, the total emission for East Asia increased from 43 ± 4 to 59 ± 4 Tg y −1 between 2000 and 2011, owing largely to the increase in emissions from China, from 39 ± 4 to 54 ± 4 Tg y −1 , while emissions in other East Asian countries remained relatively stable. For China, South Korea, and Japan, the total emissions were smaller than the prior estimates (i.e., EDGAR-4.2 FT2010 for anthropogenic emissions) by an average of 29%, 20%, and 23%, respectively. For Mongolia, Taiwan, and North Korea, the total emission was less than 2 Tg y −1 and was not significantly different from the prior. The largest reductions in emissions, compared to the prior, occurred in summer in regions important for rice agriculture suggesting that this source is overestimated in the prior. Furthermore, analysis of the isotope data suggests that the prior underestimates emissions from landfills and ruminant animals for winter 2010 to spring 2011 (no data available for other times). The inversion also found a lower average emission trend for China, 1.2 Tg y −1 compared to 2.8 Tg y −1 in the prior. This trend was not constant, however, and increased significantly after 2005, up to 2.0 Tg y −1 . Overall, the changes in emissions from China explain up to 40% of the increase in global emissions in the 2000s.

Description: The oxidizing capacity of the global atmosphere is largely determined by hydroxyl (OH) radicals and is diagnosed by analyzing methyl chloroform (CH(3)CCl(3)) measurements. Previously, large year-to-year changes in global mean OH concentrations have been inferred from such measurements, suggesting that the atmospheric oxidizing capacity is sensitive to perturbations by widespread air pollution and natural influences. We show how the interannual variability in OH has been more precisely estimated from CH(3)CCl(3) measurements since 1998, when atmospheric gradients of CH(3)CCl(3) had diminished as a result of the Montreal Protocol. We infer a small interannual OH variability as a result, indicating that global OH is generally well buffered against perturbations. This small variability is consistent with measurements of methane and other trace gases oxidized primarily by OH, as well as global photochemical model calculations.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Montzka, S A -- Krol, M -- Dlugokencky, E -- Hall, B -- Jockel, P -- Lelieveld, J -- New York, N.Y. -- Science. 2011 Jan 7;331(6013):67-9. doi: 10.1126/science.1197640.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉NOAA Earth System Research Laboratory, Boulder, CO 80305, USA. stephen.a.montzka@noaa.gov〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21212353" target="_blank"〉PubMed〈/a〉

Description: [1]  Observations of tropospheric N 2 O mixing ratio show significant variability on inter-annual timescales (0.2 ppb, 1 standard deviation). We found that inter-annual variability in N 2 O is weakly correlated with that in CFC-12 and SF 6 for the northern extra-tropics and more strongly correlated in the southern extra-tropics suggesting that inter-annual variability in all these species is influenced by large-scale atmospheric circulation changes and, for SF 6 in particular, inter-hemispheric transport. N 2 O inter-annual variability was not, however, correlated with polar lower stratospheric temperature, which is used as a proxy for stratosphere to troposphere transport in the extra-tropics. This suggests that stratosphere to troposphere transport is not a dominant factor in year-to-year variations in N 2 O growth-rate. Instead, we found strong correlations of N 2 O inter-annual variability with the Multivariate ENSO Index. The climate variables, precipitation, soil moisture and temperature were also found to be significantly correlated with N 2 O inter-annual variability, suggesting that climate-driven changes in soil N 2 O flux may be important for variations in N 2 O growth rate.

Description: The terrestrial biosphere can release or absorb the greenhouse gases, carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O), and therefore has an important role in regulating atmospheric composition and climate. Anthropogenic activities such as land-use change, agriculture and waste management have altered terrestrial biogenic greenhouse gas fluxes, and the resulting increases in methane and nitrous oxide emissions in particular can contribute to climate change. The terrestrial biogenic fluxes of individual greenhouse gases have been studied extensively, but the net biogenic greenhouse gas balance resulting from anthropogenic activities and its effect on the climate system remains uncertain. Here we use bottom-up (inventory, statistical extrapolation of local flux measurements, and process-based modelling) and top-down (atmospheric inversions) approaches to quantify the global net biogenic greenhouse gas balance between 1981 and 2010 resulting from anthropogenic activities and its effect on the climate system. We find that the cumulative warming capacity of concurrent biogenic methane and nitrous oxide emissions is a factor of about two larger than the cooling effect resulting from the global land carbon dioxide uptake from 2001 to 2010. This results in a net positive cumulative impact of the three greenhouse gases on the planetary energy budget, with a best estimate (in petagrams of CO2 equivalent per year) of 3.9 +/- 3.8 (top down) and 5.4 +/- 4.8 (bottom up) based on the GWP100 metric (global warming potential on a 100-year time horizon). Our findings suggest that a reduction in agricultural methane and nitrous oxide emissions, particularly in Southern Asia, may help mitigate climate change.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Tian, Hanqin -- Lu, Chaoqun -- Ciais, Philippe -- Michalak, Anna M -- Canadell, Josep G -- Saikawa, Eri -- Huntzinger, Deborah N -- Gurney, Kevin R -- Sitch, Stephen -- Zhang, Bowen -- Yang, Jia -- Bousquet, Philippe -- Bruhwiler, Lori -- Chen, Guangsheng -- Dlugokencky, Edward -- Friedlingstein, Pierre -- Melillo, Jerry -- Pan, Shufen -- Poulter, Benjamin -- Prinn, Ronald -- Saunois, Marielle -- Schwalm, Christopher R -- Wofsy, Steven C -- England -- Nature. 2016 Mar 10;531(7593):225-8. doi: 10.1038/nature16946.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉International Center for Climate and Global Change Research, School of Forestry and Wildlife Sciences, Auburn University, Auburn, Alabama 36849, USA. ; Department of Ecology, Evolution, and Organismal Biology, Iowa State University, Iowa 50011, USA. ; Laboratoire des Sciences du Climat et de l'Environnement, 91191 Gif sur Yvette, France. ; Department of Global Ecology, Carnegie Institution for Science, Stanford, California 94305, USA. ; Global Carbon Project, CSIRO Oceans and Atmosphere Research, GPO Box 3023, Canberra, Australian Capital Territory 2601, Australia. ; Department of Environmental Sciences, Emory University, Atlanta, Georgia 30322, USA. ; School of Earth Sciences and Environmental Sustainability, Northern Arizona University, Flagstaff, Arizona 86011, USA. ; School of Life Sciences, Arizona State University, Tempe, Arizona 85287, USA. ; College of Life and Environmental Sciences, University of Exeter, Exeter EX4 4RJ, UK. ; NOAA Earth System Research Laboratory, Global Monitoring Division, Boulder, Colorado 80305, USA. ; Environmental Science Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA. ; College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter EX4 4QF, UK. ; The Ecosystems Center, Marine Biological Laboratory, Woods Hole, Massachusetts 02543, USA. ; Institute of Ecosystems and Department of Ecology, Montana State University, Bozeman, Montana 59717, USA. ; Center for Global Change Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA. ; Woods Hole Research Center, Falmouth, Massachusetts 02540, USA. ; Department of Earth and Planetary Science, Harvard University, 29 Oxford Street, Cambridge, Massachusetts 02138, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26961656" target="_blank"〉PubMed〈/a〉

Description: Recent studies have proposed significant increases in CH 4 emissions possibly from oil and gas (O&G) production, especially for the US where O&G production has reached historically high levels over the past decade [ US EIA , 2016; Turner et al. , 2016; Hausmann et al. , 2015; Franco et al. , 2016]. In this study, we show that an ensemble of time-dependent atmospheric inversions constrained by calibrated atmospheric observations of surface CH 4 mole fraction, with some including space-based retrievals of column average CH 4 mole fractions, suggests that North American CH 4 emissions have been flat over years spanning 2000 through 2012. Estimates of emission trends using zonal gradients of column average CH 4 calculated relative to an upstream background are not easy to make due to atmospheric variability, relative insensitivity of column average CH 4 to surface emissions at regional scales, and fast zonal synoptic transport. In addition, any trends in continental enhancements of column average CH 4 are sensitive to how the upstream background is chosen, and model simulations imply that short-term (4 years or less) trends in column average CH 4 horizontal gradients of up to 1.5 ppb/yr can occur just from inter-annual transport variability acting on a strong latitudinal CH 4 gradient. Finally, trends in spatial gradients calculated from space-based column average CH 4 can be significantly biased (〉2-3 ppb/yr) due to the non-uniform and seasonally varying temporal coverage of satellite retrievals.

Description: [1]  Methane (CH 4 ), carbon dioxide (CO 2 ), carbon monoxide (CO), and C 2 –C 5 alkanes were measured throughout the Los Angeles (L.A.) basin in May and June 2010. We use these data to show that the emission ratios of CH 4 /CO and CH 4 /CO 2 in the L.A. basin are larger than expected from population-apportioned bottom-up state inventories, consistent with previously published work. We use experimentally determined CH 4 /CO and CH 4 /CO 2 emission ratios in combination with annual State of California CO and CO 2 inventories to derive a yearly emission rate of CH 4 to the L.A. basin. We further use the airborne measurements to directly derive CH 4 emission rates from dairy operations in Chino, and from the two largest landfills in the L.A. basin, and show these sources are accurately represented in the California Air Resources Board greenhouse gas inventory for CH 4 . We then use measurements of C 2 –C 5 alkanes to quantify the relative contribution of other CH 4 sources in the L.A. basin, with results differing from those of previous studies. The atmospheric data are consistent with the majority of CH 4 emissions in the region coming from fugitive losses from natural gas in pipelines and urban distribution systems and/or geologic seeps, as well as landfills and dairies. The local oil and gas industry also provides a significant source of CH 4 in the area. The addition of CH 4 emissions from natural gas pipelines and urban distribution systems and/or geologic seeps and from the local oil and gas industry is sufficient to account for the differences between the top-down and bottom-up CH 4 inventories identified in previously published work.

Description: [1]  The causes of renewed growth in the atmospheric CH 4 burden since 2007 are still poorly understood and the subject of intensive scientific discussion. Here, we present a reanalysis of global CH 4 emissions during the 2000s, based on the TM5-4DVAR inverse modeling system. We use high-accuracy surface observations from the NOAA Earth System Research Laboratory global cooperative air sampling network for 2000–2010, together with retrievals of column-averaged CH 4 mole fractions from the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) instrument onboard ENVISAT from 2003 onwards. [2]  Using climatological OH fields, derived global total emissions for 2007–2010 are 16–20 Tg CH 4 /yr higher than for 2003–2005. Most of the inferred increase was located in the tropics (9–14 Tg CH 4 /yr) and mid-latitudes of the northern hemisphere (6–8 Tg CH 4 /yr), while no significant trend was derived for Arctic latitudes. The atmospheric increase can be attributed mainly to an increase of anthropogenic emissions. However, the derived trend in anthropogenic emissions is significantly smaller than the one estimated in the EDGARv4.2 emission inventory. Superimposed on the increasing trend in anthropogenic CH 4 emissions are significant inter-annual variations (IAV) of CH 4 emissions from wetlands (up to ±10 Tg CH 4 /yr), and biomass burning (up to ±7 Tg CH 4 /yr). [3]  Various sensitivity experiments have been performed to investigate the impact of the SCIAMACHY observations (compared to inversions using only surface observations), of the OH fields used, and of a priori emission inventories on the derived CH 4 emission trends and their inter-annual variability. Despite significant differences among these sensitivity experiments in their latitudinal attribution of IAV of CH 4 emissions, they show a reasonably consistent picture regarding the IAV aggregated on larger latitude bands. Furthermore, all sensitivity experiments show very similar performance against a comprehensive independent dataset of observations used for validation, including NOAA ship and aircraft profile samples, HIPPO aircraft transects, and CARIBIC aircraft data. Comparison of model simulations with BARCA aircraft measurements, however, show significantly better agreement in the free troposphere over the Amazon for the inversions using the SCIAMACHY and NOAA surface observations compared to inversions using only the surface observations, demonstrating the usefulness of the satellite measurements to better constrain tropical CH 4 emissions.