Early anthropogenic CH 4 emissions and the variation of CH 4 and 13 CH 4 over the last millennium (original) (raw)
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Atmospheric Chemistry and Physics, 2011
The availability δ 13 C-CH 4 measurements from atmospheric samples has significantly improved in recent years, which allows the construction of time series spanning up to about 2 decades. We have used these measurements to investigate the cause of the methane growth rate decline since 1980, with a special focus on the period 1998-2006 5 when the methane growth came to a halt. The constraints provided by the CH 4 and δ 13 C-CH 4 measurements are used to construct hypothetic source and sink scenarios, which are translated into corresponding atmospheric concentrations using the atmospheric transport model TM3 for evaluation against the measurements. The base scenario, composed of anthropogenic emissions according to Edgar 4, constant emissions 10 from natural sources, and a constant atmospheric lifetime, overestimates the observed global growth rates of CH 4 and δ 13 C-CH 4 by, respectively, 10 ppb yr −1 and 0.02‰ yr −1 after the year 2000. It proves difficult to repair this inconsistency by modifying trends in emissions only, notably because a temporary reduction of isotopically light sources, such as natural wetlands, leads to a further increase of δ 13 C-CH 4 . Furthermore, our 15 results are difficult to reconcile with the estimated increase of 5 Tg CH 4 yr −1 in emissions from fossil fuel use in the period 2000-2005.
Variations in global methane sources and sinks during 1910–2010
Atmospheric Chemistry and Physics Discussions, 2014
Atmospheric methane (CH<sub>4</sub>) increased from ~900 ppb (parts per billion, or nanomoles per mole of dry air) in 1900 to ~1800 ppb during the 2000s at a rate unprecedented in any observational records. However, the causes of the CH<sub>4</sub> increase are poorly understood. Here we use initial emissions from bottom-up inventories for anthropogenic sources, emissions from wetlands and rice paddies simulated by a terrestrial biogeochemical model, and an atmospheric general circulation model (AGCM)-based chemistry-transport model (i.e. ACTM) to simulate atmospheric CH<sub>4</sub> concentrations for 1910 to 2010. The ACTM simulations are compared with the CH<sub>4</sub> concentration records reconstructed from Antarctic and Arctic ice cores and firn air samples, and from direct measurements since the 1980s at multiple sites around the globe. The differences between ACTM simulations and observed CH<sub>4</sub> concentratio...
Changing concentration, lifetime and climate forcing of atmospheric methane
2002
Previous studies on ice core analyses and recent in situ measurements have shown that CH 4 has increased from about 0.75 to 1.73 mmol/mol during the past 150 years. Here, we review sources and sink estimates and we present global 3D model calculations, showing that the main features of the global CH 4 distribution are well represented.
Methane and Global Environmental Change
Annual Review of Environment and Resources, 2018
Global atmospheric methane concentrations have continued to rise in recent years, having already more than doubled since the Industrial Revolution. Further environmental change, especially climate change, in the twenty-first century has the potential to radically alter global methane fluxes. Importantly, changes in temperature, precipitation, and net primary production may induce positive climate feedback effects in dominant natural methane sources such as wetlands, soils, and aquatic ecosystems. Anthropogenic methane sources may also be impacted, with a risk of enhanced emissions from the energy, agriculture, and waste sectors. Here, we review the global sources of methane, the trends in fluxes by source and sector, and their possible evolution in response to future environmental change. We discuss ongoing uncertainties in flux estimation and projection, and highlight the great potential for multisector methane mitigation as part of wider global climate change policy.
Atmospheric methane and global change
Earth-science Reviews, 2002
Methane (CH 4 ) is the most abundant organic trace gas in the atmosphere. In the distant past, variations in natural sources of methane were responsible for trends in atmospheric methane levels recorded in ice cores. Since the 1700s, rapidly growing human activities, particularly in the areas of agriculture, fossil fuel use, and waste disposal, have more than doubled methane emissions. Atmospheric methane concentrations have increased by a factor of 2 -3 in response to this increase, and continue to rise. These increasing concentrations have raised concern due to their potential effects on atmospheric chemistry and climate. Methane is important to both tropospheric and stratospheric chemistry, significantly affecting levels of ozone, water vapor, the hydroxyl radical, and numerous other compounds. In addition, methane is currently the second most important greenhouse gas emitted from human activities. On a per molecule basis, it is much more effective a greenhouse gas than additional CO 2 . In this review, we examine past trends in the concentration of methane in the atmosphere, the sources and sinks that determine its growth rate, and the factors that will affect its growth rate in the future. We also present current understanding of the effects of methane on atmospheric chemistry, and examine the direct and indirect impacts of atmospheric methane on climate. D
The Global Methane Budget 2000–2017
Earth System Science Data Discussions
Understanding and quantifying the global methane (CH 4) budget is important for assessing realistic pathways to mitigate climate change. Atmospheric emissions and concentrations of CH 4 are continuing to increase, making CH 4 the second most important human-influenced greenhouse gas in terms of climate forcing, after carbon dioxide (CO 2). Assessing the relative importance of CH 4 in comparison to CO 2 is complicated by its shorter atmospheric lifetime, stronger warming potential, and atmospheric growth rate variations over the past decade, the causes of which are still debated. Two major difficulties in reducing uncertainties arise from the variety of geographically overlapping CH 4 sources and from the destruction of CH 4 by short-lived hydroxyl radicals (OH). To address these difficulties, we have established a consortium of multidisciplinary scientists under the umbrella of the Global Carbon Project to synthesize and stimulate new research aimed at improving and regularly updating the global methane budget. Following Saunois et al. (2016), we present here the second version of the living review paper dedicated to the decadal methane budget, integrating results of top-down studies (atmospheric observations within an atmospheric inverse-modelling framework) and bottom-up estimates (including process-based models for estimating land surface emissions and atmospheric chemistry, inventories of anthropogenic emissions, and data-driven extrapolations). For the 2008-2017 decade, global methane emissions are estimated by atmospheric inversions (top-down approach) to be 572 Tg CH 4 yr-1 (range 538-593, corresponding to the minimum and maximum estimates of the ensemble), of which 357 Tg CH 4 yr-1 or ~60% are attributed to anthropogenic sources (range 50
Estimates of global anthropogenic methane emissions 1860-1993
Chemosphere, 1996
This paper provides the first time series estimates of global anthropogenic methane emissions from the mid-19th century to the present. Our purpose is to provide time series estimates of anthropogenic methane emissions for global climate models estimated or calibrated using historical time series data. Previous estimates of methane emissions include "top-down" (deconvolution) estimates of total emissions, estimates of global anthropogenic emissions for the 16th century, and various estimates of anthropogenic and natural emissions in the 1980s and 1990s. This study uses previously published point estimates for the 16th century and the 1980s and early 90s and a variety of historical time series of proxy variables to estimate a time series of global anthropogenic methane emissions. We find that anthropogenic methane emissions have increased from about 80 million tonnes per annum in 1860 to close to 380 million tonnes today. The relative importance of various activities in generating methane emissions has changed over time and continues to change. The rate of increase now may be slowing. A comparison with the estimates generated by Khalil and Rasmussen suggests that natural sources of methane have declined over the period. There are, however, great uncertainties in these estimates which future research may be able to reduce.