Enhanced methane emissions from tropical wetlands during the 2011 La Niña

Pandey, Sudhanshu; Houweling, Sander; Krol, Maarten; Aben, I.; Monteil, Guillaume; Nechita-Banda, Narcisa; Dlugokencky, Edward J.; Detmers, R. G.; Hasekamp, Otto; Xu, Xiyan; Riley, William J.; Poulter, Benjamin; Zhang, Zhen; McDonald, K. C.; White, James W. C.; Bousquet, Philippe; Röckmann, T.

doi:10.1038/srep45759

Cited by 56 publications

(65 citation statements)

References 59 publications

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“…However, according to Figure 2b this zonal anomaly can be explained largely by transport, as found in our global analysis already. This finding is consistent with increased wetland emissions in the Northern Tropics reported by Pandey et al (2017). This is consistent with the hypothesis of Nisbet et al (2016) that emissions in the Southern Tropics were enhanced during 2014 as it was an exceptionally warm and wet year in Southern Africa and Amazonia.…”

Section: Zonal Growth Ratessupporting

confidence: 91%

Influence of Atmospheric Transport on Estimates of Variability in the Global Methane Burden

Pandey

Houweling

Krol

et al. 2019

Geophysical Research Letters

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We quantify the impact of atmospheric transport and limited marine boundary layer sampling on changes in global and regional methane burdens estimate using tracer transport model simulations with annually repeating methane emissions and sinks but varying atmospheric transport patterns. We find the 1σ error due to this transport and sampling effect on annual global methane increases to be 1.11 ppb/year and on zonal growth rates to be 3.8 ppb/year, indicating that it becomes more critical at smaller spatiotemporal scales. We also find that the trends in inter‐hemispheric and inter‐polar difference of methane are significantly influenced by the effect. Contrary to a negligible trend in the inter‐hemispheric difference of measurements, we find, after adjusting for the transport and sampling, a trend of 0.37 ± 0.06 ppb/year. This is consistent with the emission trend from a 3‐D inversion of the measurements, suggesting a faster increase in emissions in the Northern Hemisphere than in the Southern Hemisphere.

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Section: Zonal Growth Ratessupporting

confidence: 91%

Influence of Atmospheric Transport on Estimates of Variability in the Global Methane Burden

Pandey

Houweling

Krol

et al. 2019

Geophysical Research Letters

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“…Specifically, the 0.8 ppm step-like increase in this difference between 2009 and 2010 was attributed to the opening and closing of the upper-tropospheric equatorial westerly duct (Waugh and Funatsu, 2003), with an open-duct pattern from July 2008 to June 2009 (fast IH exchange), followed by closed-duct conditions from July 2009 to June 2010 (slow IH exchange). Confirming this mechanism, Pandey et al (2017) also found faster IH transport of CH 4 during the strong La Niña in 2011 using the TM5 CTM. The timescale of IH transport is an important parameter for atmospheric inversion studies.…”

Section: Introductionmentioning

confidence: 48%

Age of air as a diagnostic for transport timescales in global models

et al. 2018

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Abstract. This paper presents the first results of an age-ofair (AoA) inter-comparison of six global transport models. Following a protocol, three global circulation models and three chemistry transport models simulated five tracers with boundary conditions that grow linearly in time. This allows for an evaluation of the AoA and transport times associated with inter-hemispheric transport, vertical mixing in the troposphere, transport to and in the stratosphere, and transport of air masses between land and ocean. Since AoA is not a directly measurable quantity in the atmosphere, simulations of 222 Rn and SF 6 were also performed. We focus this first analysis on averages over the period 2000-2010, taken from longer simulations covering the period 1988-2014. We find that two models, NIES and TOMCAT, show substantially slower vertical mixing in the troposphere compared to other models (LMDZ, TM5, EMAC, and ACTM). However, while the TOMCAT model, as used here, has slow transport between the hemispheres and between the atmosphere over land and ocean, the NIES model shows efficient horizontal mixing and a smaller latitudinal gradient in SF 6 compared to the other models and observations. We find consistent differences between models concerning vertical mixing of the troposphere, expressed as AoA differences and modelled 222 Rn gradients between 950 and 500 hPa. All models agree, however, on an interesting asymmetry in inter-hemispheric mixing, with faster transport from the Northern Hemisphere surface to the Southern Hemisphere than vice versa. This is attributed to a rectifier effect caused by a stronger seasonal cycle in boundary layer venting over Northern Hemispheric land masses, and possibly to a related asymmetric position of the intertropical convergence zone. The calculated AoA in the mid-upper stratosphere varies considerably among the models (4-7 years). Finally, we find that the inter-model differences are generally larger than differences in AoA that result from using the same model with a different resolution or convective parameterisation. Taken together, the AoA model inter-comparison provides a useful addition to traditional approaches to evaluate transport timescales. Results highlight that inter-model differences associated with resolved transport (advection, reanalysis data, nudging) and parameterised transport (convection, boundary layer mixing) are still large and require further analysis. For this purpose, all model output and analysis software are available.

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“…Natural emissions would be reduced under sulfate geoengineering for three main reasons: (1) a reduction in surface temperatures that would, in turn, be connected with a highly probable reduction in rainfall, compared with the predicted increase under most future warming scenarios (Trenberth, 1998;Pandey et al, 2017); this would reduce the amount of CH 4 produced by wetland areas, thus affecting the atmospheric methane concentration; (2) the increased surface deposition of sulfate under SG conditions would itself produce changes in emissions from wetlands (Gauci et al, 2008); (3) SG could help avert one of the possible risks of global warming, i.e., the emission of methane from permafrost thawing (Kohnert et al, 2017). It remains to be investigated how much these effects, together, could offset the photochemical CH 4 increase resulting from our study.…”

Section: Discussionmentioning

confidence: 99%

Sulfate geoengineering impact on methane transport and lifetime: results from the Geoengineering Model Intercomparison Project (GeoMIP)

et al. 2017

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Abstract. Sulfate geoengineering (SG), made by sustained injection of SO 2 in the tropical lower stratosphere, may impact the CH 4 abundance through several photochemical mechanisms affecting tropospheric OH and hence the methane lifetime. (a) The reflection of incoming solar radiation increases the planetary albedo and cools the surface, with a tropospheric H 2 O decrease. (b) The tropospheric UV budget is upset by the additional aerosol scattering and stratospheric ozone changes: the net effect is meridionally not uniform, with a net decrease in the tropics, thus producing less tropospheric O( 1 D). (c) The extratropical downwelling motion from the lower stratosphere tends to increase the sulfate aerosol surface area density available for heterogeneous chemical reactions in the mid-to-upper troposphere, thus reducing the amount of NO x and O 3 production. (d) The tropical lower stratosphere is warmed by solar and planetary radiation absorption by the aerosols. The heating rate perturbation is highly latitude dependent, producing a stronger meridional component of the Brewer-Dobson circulation. The net effect on tropospheric OH due to the enhanced stratosphere-troposphere exchange may be positive or negative depending on the net result of different superimposed species perturbations (CH 4 , NO y , O 3 , SO 4 ) in the extratropical upper troposphere and lower stratosphere (UTLS). In addition, the atmospheric stabilization resulting from the tropospheric cooling and lower stratospheric warming favors an additional decrease of the UTLS extratropical CH 4 by lowering the horizontal eddy mixing. Two climate-chemistry coupled models are used to explore the above radiative, chemical and dynamical mechanisms affecting CH 4 transport and lifetime (ULAQ-CCM and GEOSCCM). The CH 4 lifetime may become significantly longer (by approximately 16 %) with a sustained injection of 8 Tg-SO 2 yr −1 starting in the year 2020, which implies an increase of tropospheric CH 4 (200 ppbv) and a positive indirect radiative forcing of sulfate geoengineering due to CH 4 changes (+0.10 W m −2 in the 2040-2049 decade and +0.15 W m −2 in the 2060-2069 decade).

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Enhanced methane emissions from tropical wetlands during the 2011 La Niña

Cited by 56 publications

References 59 publications

Influence of Atmospheric Transport on Estimates of Variability in the Global Methane Burden

Influence of Atmospheric Transport on Estimates of Variability in the Global Methane Burden

Age of air as a diagnostic for transport timescales in global models

Sulfate geoengineering impact on methane transport and lifetime: results from the Geoengineering Model Intercomparison Project (GeoMIP)

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