Atmospheric constraints on global emissions of methane from plants (original) (raw)
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Global Change Biology, 2020
Forest soils are the most important terrestrial sink of atmospheric methane (CH 4). Climatic, soil and anthropogenic drivers affect CH 4 fluxes, but it is poorly known the relative weight of each driver and whether all drivers have similar effects across forest biomes. We compiled a database of 478 in situ estimations of CH 4 fluxes in forest soils from 191 peer reviewed studies. All forest biome (boreal, temperate, tropical and subtropical) but savannas act on average as CH 4 sinks, which presented positive fluxes in 65% of the sites. Mixed effects models showed that combined climatic and edaphic variables had the best support, but anthropogenic factors did not have a significant effect on CH 4 fluxes at global scale. This model explained only 19% of the variance in soil CH 4 flux which decreased with declines in precipitation and increases in temperature, and with increases in soil organic carbon, bulk density and soil acidification. The effects of these drivers were inconsistent across biomes, increasing the model explanation of observed variance to 34% when the drivers have a different slope for each biome. Despite this limited explanatory value, which could be related to the use of soil variables calculated at coarse scale (~1km); our study shows that soil CH 4 fluxes in forests are determined by different environmental variables in different biomes. The most sensitive system to all studied drivers were the temperate forests, while boreal forests were insensitive to climatic variables, but highly sensitive to edaphic factors. Subtropical forests and savannas responded similarly to climatic variables, but differed in their response to soil factors. Our results suggest that the increase in temperature predicted in the framework of climate change would promote CH 4 emission (or reduce CH 4 sink) in subtropical and savannas forests, have no influence in boreal and temperate forests and promote uptake in tropical forests.
Global Biogeochemical Cycles, 2004
We present a time-dependent inverse modeling approach to estimate the magnitude of CH4 emissions and the average isotopic signature of the combined source processes from geographical regions based on the observed spatiotemporal distribution of CH4 and C-13/C-12 isotopic ratios in CH4. The inverse estimates of the isotopic signature of the sources are used to partition the regional source estimates into three groups of source processes based on their isotopic signatures. Compared with bottom-up estimates, the inverse estimates call for larger CH4 fluxes in the tropics (266 +/-25 Tg CH4/yr) and southern extratropics (98 +/-15 Tg CH4/yr) and reduced fluxes in the northern extratropics (252 +/-18 Tg CH4/yr). The observations of C-13/ C-12 isotopic ratios in CH4 indicate that the large a posteriori CH4 source in the tropics and Southern Hemisphere is attributable to a combination both bacterial sources and biomass burning and support relatively low estimates of fossil CH4 emissions. 12 [1] We present a time-dependent inverse modeling approach to estimate the magnitude of 13 CH 4 emissions and the average isotopic signature of the combined source processes from 14 geographical regions based on the observed spatiotemporal distribution of CH 4 and 15 13 C/ 12 C isotopic ratios in CH 4 . The inverse estimates of the isotopic signature of the 16 sources are used to partition the regional source estimates into three groups of source 17 processes based on their isotopic signatures. Compared with bottom-up estimates, the 18 inverse estimates call for larger CH 4 fluxes in the tropics (266 ± 25 Tg CH 4 /yr) and 19 southern extratropics (98 ± 15 Tg CH 4 /yr) and reduced fluxes in the northern extratropics 20 (252 ± 18 Tg CH 4 /yr). The observations of 13 C/ 12 C isotopic ratios in CH 4 indicate that the 21 large a posteriori CH 4 source in the tropics and Southern Hemisphere is attributable to 22 a combination both bacterial sources and biomass burning and support relatively low 23 estimates of fossil CH 4 emissions. estimating the sources and sinks of CH 4 through models 48 of the source processes and combining local observations of 49 CH 4 emissions or emission ratios with land use inventories, 50 energy use or agricultural data, or other relevant statistical 51 information [e.g., Matthews and Fung, 1987; Aselmann and 52 Crutzen, 1989; Olivier et al., 1996; Levine et al., 2000; 53 Kaplan, 2001]. However, owing to the large spatial and 54 temporal variability of many of the source processes, these 55 estimates are associated with a great deal of uncertainty. 56 Forward model simulations which determine the atmo-57 spheric spatiotemporal distribution of CH 4 based on esti-58 mates of the sources and sinks have found that these 59 bottom-up estimates lead to an overestimate of the inter-60 hemispheric gradient relative to the atmospheric observa-61 tions [e.g., Fung et al., 1991; Hein et al., 1997; Houweling 62 et al., 1999] (Figure 1), suggesting our process-level 63 understanding of the CH 4 cycle is incomplete. In addition, 64 bottom-up estimates often do not account for interannual
Atmospheric Chemistry and Physics
We present a single box atmospheric chemistry model involving atmospheric methane (CH 4 ), carbon monoxide (CO) and radical hydroxyl (OH) to analyze atmospheric CH 4 concentrations from 1984 to 2008. When OH is allowed to vary, the modeled CH 4 is 20 ppb higher than observations from the NOAA/ESRL and AGAGE net-5 works for the end of 2008. However, when the OH concentration is held constant at 10 6 molecule cm −3 , the simulated CH 4 shows a trend approximately equal to observations. Both simulations show a clear slowdown in the CH 4 growth rate during recent decades, from about 13 ppb yr −1 in 1984 to less than 5 ppb yr −1 in 2003. Furthermore, if
Stable isotopes provide revised global limits of aerobic methane emissions from plants
Atmospheric Chemistry and Physics, 2007
Recently discovered a surprising new source of methane -terrestrial plants under aerobic conditions, with an estimated global production of 62-236 Tg yr −1 by an unknown mechanism. This is ∼10-50% of the annual total of methane entering the modern atmosphere and ∼30-100% of annual methane entering 5 the pre-industrial (0 to 1700 AD) atmosphere. Here we test this reported global production of methane from plants against ice core records of atmospheric methane concentration (CH 4 ) and stable carbon isotope ratios (δ 13 CH 4 ) over the last 2000 years. Our top-down approach determines that global plant emissions must be much lower than proposed by during the last 2000 years and are likely to lie 10 in the range 0-46 Tg yr −1 . 6, 5867-5875, 2006 Abstract ACPD 6, 5867-5875, 2006 Abstract ACPD 6, 5867-5875, 2006
δ 13 C methane source signatures from tropical wetland and rice field emissions
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
The atmospheric methane (CH 4 ) burden is rising sharply, but the causes are still not well understood. One factor of uncertainty is the importance of tropical CH 4 emissions into the global mix. Isotopic signatures of major sources remain poorly constrained, despite their usefulness in constraining the global methane budget. Here, a collection of new δ 13 C CH 4 signatures is presented for a range of tropical wetlands and rice fields determined from air samples collected during campaigns from 2016 to 2020. Long-term monitoring of δ 13 C CH 4 in ambient air has been conducted at the Chacaltaya observatory, Bolivia and Southern Botswana. Both long-term records are dominated by biogenic CH 4 sources, with isotopic signatures expected from wetland sources. From the longer-term Bolivian record, a seasonal isotopic shift is observed corresponding to wetland extent suggesting that there is input of relatively isotopically light CH 4 to the atmosphere during periods of reduced wetland exte...