Wetland methane emissions during the Last Glacial Maximum estimated from PMIP2 simulations: Climate, vegetation, and geographic controls

Weber, Shlomo; Drury, Anna Joy; Toonen, W.H.J.; Weele, M. van

doi:10.1029/2009jd012110

Cited by 41 publications

(70 citation statements)

References 33 publications

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“…The resulting estimates of the reductions in methane emissions at the warm LGM relative to the preindustrial (between 46 and 62 %) are comparable to the Murray et al (2014) "best estimate" of 50 %. However, the range of our implied values exceed those derived from prior model studies of wetland emission changes (Valdes et al, 2005;Kaplan et al, 2006;Weber et al 2010). Our findings also have implications for radiative forcing estimates of SOA on preindustrial-present and glacial-interglacial timescales.…”

Section: P Achakulwisut Et Al: Uncertainties In Isoprene Photochemicontrasting

confidence: 51%

“…However, the range of values derived from the loss of methane by OH across our sensitivity simulations exceeds the 29-42 % decrease in wetland emissions simulated by the PMIP2 ensemble members (Weber et al, 2010) and the 16 and 23 % decreases in natural methane emissions simulated by Kaplan et al (2006) and Valdes et al (2005), respectively.…”

Section: Implications For the Methane Budgetmentioning

confidence: 98%

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Uncertainties in isoprene photochemistry and emissions: implications for the oxidative capacity of past and present atmospheres and for climate forcing agents

et al. 2015

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Abstract. Isoprene and its oxidation products are major players in the oxidative chemistry of the troposphere. Current understanding of the factors controlling biogenic isoprene emissions and of the fate of isoprene oxidation products in the atmosphere has been evolving rapidly. We use a climate-biosphere-chemistry modeling framework to evaluate the sensitivity of estimates of the tropospheric oxidative capacity to uncertainties in isoprene emissions and photochemistry. Our work focuses on two climate transitions: from the Last Glacial Maximum (LGM, 19 000-23 000 years BP) to the preindustrial (1770s) and from the preindustrial to the present day (1990s). We find that different oxidants have different sensitivities to the uncertainties tested in this study. Ozone is relatively insensitive, whereas OH is the most sensitive: changes in the global mean OH levels for the LGM-to-preindustrial transition range between −29 and +7 % and those for the preindustrial-to-present-day transition range between −8 and +17 % across our simulations. We find little variability in the implied relative LGMpreindustrial difference in methane emissions with respect to the uncertainties tested in this study. Conversely, estimates of the preindustrial-to-present-day and LGM-to-preindustrial changes in the global burden of secondary organic aerosol (SOA) are highly sensitive. We show that the linear relationship between tropospheric mean OH and tropospheric mean ozone photolysis rates, water vapor, and total emissions of NO x and reactive carbon -first reported in Murray et al. (2014) -does not hold across all periods with the new isoprene photochemistry mechanism. This study demonstrates how inadequacies in our current understanding of isoprene emissions and photochemistry impede our ability to constrain the oxidative capacities of the present and past atmospheres, its controlling factors, and the radiative forcing of some short-lived species such as SOA over time.

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Section: P Achakulwisut Et Al: Uncertainties In Isoprene Photochemicontrasting

confidence: 51%

Section: Implications For the Methane Budgetmentioning

confidence: 98%

Uncertainties in isoprene photochemistry and emissions: implications for the oxidative capacity of past and present atmospheres and for climate forcing agents

et al. 2015

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“…Thus, the impact of the additional complexity of the hydrological scheme employed in ORCHIDEE-WET compared to in SDGVM has only a limited effect on the LGM-PI difference in CH 4 emissions. The change in wetland extent between LGM and PI is partially due to the change in both continental ice sheets (decrease of land area available for wetlands) and continental shelves (increase in land area available for wetlands), which are named "geographic effects" in Weber et al (2010). The contribution of the "geographic effects" to the change in emission is close in the two models.…”

Section: Factors Explaining the Difference In The Lgm-pi Change In Emmentioning

confidence: 82%

“…Large uncertainty remains surrounding to what extent the main natural source (wetlands) contributed to the glacialinterglacial change in [CH 4 ], and whilst earlier bottom-up modelling studies could not explain the glacial-interglacial change in [CH 4 ] with a reduction in wetland CH 4 emissions alone in response to cooling and change in hydrological cycle (Kaplan et al, 2006;Valdes et al, 2005), more recent studies suggest that a modification in sink strength is neither required (Weber et al, 2010) nor reproduced by atmospheric chemistry model simulations (Levine et al, 2011).…”

Section: B Ringeval Et Al: Wetland Ch 4 Emissions During Dansgaard-mentioning

confidence: 99%

Response of methane emissions from wetlands to the Last Glacial Maximum and an idealized Dansgaard–Oeschger climate event: insights from two models of different complexity

et al. 2013

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Abstract.The role of different sources and sinks of CH 4 in changes in atmospheric methane ([CH 4 ]) concentration during the last 100 000 yr is still not fully understood. In particular, the magnitude of the change in wetland CH 4 emissions at the Last Glacial Maximum (LGM) relative to the pre-industrial period (PI), as well as during abrupt climatic warming or Dansgaard-Oeschger (D-O) events of the last glacial period, is largely unconstrained. In the present study, we aim to understand the uncertainties related to the parameterization of the wetland CH 4 emission models relevant to these time periods by using two wetland models of different complexity (SDGVM and ORCHIDEE). These models have been forced by identical climate fields from low-resolution coupled atmosphere-ocean general circulation model (FA-MOUS) simulations of these time periods. Both emission models simulate a large decrease in emissions during LGM in comparison to PI consistent with ice core observations and previous modelling studies. The global reduction is much larger in ORCHIDEE than in SDGVM (respectively −67 and −46 %), and whilst the differences can be partially explained by different model sensitivities to temperature, the major reason for spatial differences between the models is the inclusion of freezing of soil water in ORCHIDEE and the resultant impact on methanogenesis substrate availability in boreal regions. Besides, a sensitivity test performed with ORCHIDEE in which the methanogenesis substrate sensitivity to the precipitations is modified to be more realistic gives a LGM reduction of −36 %. The range of the global LGM decrease is still prone to uncertainty, and here we underline its sensitivity to different process parameterizations. Over the course of an idealized D-O warming, the magnitude of the change in wetland CH 4 emissions simulated by the two models at global scale is very similar at around 15 Tg yr −1 , but this is only around 25 % of the icecore measured changes in [CH 4 ]. The two models do show regional differences in emission sensitivity to climate with much larger magnitudes of northern and southern tropical anomalies in ORCHIDEE. However, the simulated northern and southern tropical anomalies partially compensate each other in both models limiting the net flux change. Future work may need to consider the inclusion of more detailed wetland processes (e.g. linked to permafrost or tropical floodplains), other non-wetland CH 4 sources or different patterns of D-O climate change in order to be able to reconcile emission estimates with the ice-core data for rapid CH 4 events.

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“…The earliest attempt at wetland modelling for the purpose of estimating wetland CH 4 emissions was designed to estimate wetland emissions during the Last Glacial Maximum (LGM, ∼ 21 ka; Kaplan, 2002). The simple scheme of Kaplan (2002) used threshold values of slope and soil moisture content to define wetland areas, with the soil moisture calculated by an equilibrium vegetation model (BIOME4); an approach adopted by other models (Shindell et al, 2004;Weber et al, 2010;Avis et al, 2011). Later schemes used land cover datasets to outline peatland regions (Wania et al, 2009a(Wania et al, , 2010Spahni et al, 2011), and/or satellite-derived inundation datasets to prescribe wetlands either directly (Hodson et al, 2011;Ringeval et al, 2010), or indirectly Riley et al, 2011).…”

Section: Introductionmentioning

confidence: 99%

Present state of global wetland extent and wetland methane modelling: methodology of a model inter-comparison project (WETCHIMP)

Wania

Melton²,

Hodson³

et al. 2013

Geosci. Model Dev.

187

180

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Abstract. The Wetland and Wetland CH 4 Intercomparison of Models Project (WETCHIMP) was created to evaluate our present ability to simulate large-scale wetland characteristics and corresponding methane (CH 4 ) emissions. A multi-model comparison is essential to evaluate the key uncertainties in the mechanisms and parameters leading to methane emissions. Ten modelling groups joined WETCHIMP to run eight global and two regional models with a common experimental protocol using the same climate and atmospheric carbon dioxide (CO 2 ) forcing datasets. We reported the main conclusions from the intercomparison effort in a companion paper (Melton et al., 2013). Here we provide technical details for the six experiments, which included an equilibrium, a transient, and an optimized run plus three sensitivity experiments (temperature, precipitation, and atmospheric CO 2 concentration). The diversity of approaches used by the models is summarized through a series of conceptual figures, and is used to evaluate the wide range of wetland extent and CH 4 fluxes predicted by the models in the equilibrium run. We discuss relationships among the various approaches and patterns in consistencies of these model predictions. Within this group of models, there are three broad classes of methods used to estimate wetland extent: prescribed based on wetland distribution maps, prognostic relationships between hydrological states based on satellite observations, and explicit hydrological mass balances. A larger variety of approaches was used to estimate the net CH 4 fluxes from wetland systems. Even though modelling of wetland extent and CH 4 emissions has progressed significantly over recent decades, large uncertainties still exist when estimating CH 4 emissions: there is little consensus on model structure or complexity due to knowledge gaps, different aims of the models, and the range of temporal and spatial resolutions of the models.

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Wetland methane emissions during the Last Glacial Maximum estimated from PMIP2 simulations: Climate, vegetation, and geographic controls

Cited by 41 publications

References 33 publications

Uncertainties in isoprene photochemistry and emissions: implications for the oxidative capacity of past and present atmospheres and for climate forcing agents

Uncertainties in isoprene photochemistry and emissions: implications for the oxidative capacity of past and present atmospheres and for climate forcing agents

Response of methane emissions from wetlands to the Last Glacial Maximum and an idealized Dansgaard–Oeschger climate event: insights from two models of different complexity

Present state of global wetland extent and wetland methane modelling: methodology of a model inter-comparison project (WETCHIMP)

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