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"Atmospheric methane"
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Bipolar carbon and hydrogen isotope constraints on the Holocene methane budget
Atmospheric methane concentration shows a well-known decrease over the first half of the Holocene following the Northern Hemisphere summer insolation before it started to increase again to preindustrial values. There is a debate about what caused this change in the methane concentration evolution, in particular, whether an early anthropogenic influence or natural emissions led to the reversal of the atmospheric CH4 concentration evolution. Here, we present new methane concentration and stable hydrogen and carbon isotope data measured on ice core samples from both Greenland and Antarctica over the Holocene. With the help of a two-box model and the full suite of CH4 parameters, the new data allow us to quantify the total methane emissions in the Northern Hemisphere and Southern Hemisphere separately as well as their stable isotopic signatures, while interpretation of isotopic records of only one hemisphere may lead to erroneous conclusions. For the first half of the Holocene our results indicate an asynchronous decrease in Northern Hemisphere and Southern Hemisphere CH4 emissions by more than 30 Tg CH4 yr−1 in total, accompanied by a drop in the northern carbon isotopic source signature of about −3 ‰. This cannot be explained by a change in the source mix alone but requires shifts in the isotopic signature of the sources themselves caused by changes in the precursor material for the methane production. In the second half of the Holocene, global CH4 emissions increased by about 30 Tg CH4 yr−1, while preindustrial isotopic emission signatures remained more or less constant. However, our results show that this early increase in methane emissions took place in the Southern Hemisphere, while Northern Hemisphere emissions started to increase only about 2000 years ago. Accordingly, natural emissions in the southern tropics appear to be the main cause of the CH4 increase starting 5000 years before present, not supporting an early anthropogenic influence on the global methane budget by East Asian land use changes.
Journal Article
Methane and Climate Change
Methane is a powerful greenhouse gas and is estimated to be responsible for approximately one-fifth of man-made global warming. Per kilogram, it is 25 times more powerful than carbon dioxide over a 100-year time horizon -- and global warming is likely to enhance methane release from a number of sources. Current natural and man-made sources include many where methane-producing micro-organisms can thrive in anaerobic conditions, particularly ruminant livestock, rice cultivation, landfill, wastewater, wetlands and marine sediments.
This timely and authoritative book provides the only comprehensive and balanced overview of our current knowledge of sources of methane and how these might be controlled to limit future climate change. It describes how methane is derived from the anaerobic metabolism of micro-organisms, whether in wetlands or rice fields, manure, landfill or wastewater, or the digestive systems of cattle and other ruminant animals. It highlights how sources of methane might themselves be affected by climate change. It is shown how numerous point sources of methane have the potential to be more easily addressed than sources of carbon dioxide and therefore contribute significantly to climate change mitigation in the 21st century.
eBook
Spatio-Temporal Patterns of Methane Emissions from 2019 Onwards: A Satellite-Based Comparison of High- and Low-Emission Regions
Methane (CH4) is a potent greenhouse gas with a significant impact on short- and medium-term climate forcing, and its atmospheric concentration has been increasing rapidly in recent decades. This study aims to analyze spatio-temporal patterns of atmospheric methane concentrations between 2019 and 2025, focusing on comparisons between regions characterized by high and low emission intensities. Level-3 XCH4 data from the TROPOspheric Monitoring Instrument (TROPOMI) onboard the Sentinel-5 Precursor satellite were used, which were aggregated into seasonal and annual composites. High-emission regions, such as the Mekong Delta, Nile Delta, Eastern Uttar Pradesh and Bihar, Central Thailand, Lake Victoria Basin, and Eastern Arkansas, were contrasted with low-emission areas including Patagonia, the Mongolian Steppe, Northern Scandinavia, the Australian Outback, the Sahara Desert, and the Canadian Shield. The results show that high-emission regions exhibit substantially higher seasonal amplitude in XCH4 concentrations, with an average seasonal variation of approximately 30.00 ppb, compared to 17.39 ppb in low-emission regions. Methane concentrations generally peaked at the end of the year (Q4) and reached their lowest levels during the first half of the year (Q1 or Q2), particularly in agriculturally dominated regions. Principal component and cluster analyses further confirmed a strong spatial differentiation between high- and low-emission regions based on both temporal trends and seasonal behavior. These findings demonstrate the potential of satellite remote sensing to monitor regional methane dynamics and highlight the need for targeted mitigation strategies in major agricultural and wetland zones.
Journal Article
Atmospheric methane control mechanisms during the early Holocene
Understanding processes controlling the atmospheric methane (CH4) mixing ratio is crucial to predict and mitigate future climate changes in this gas. Despite recent detailed studies of the last ∼ 1000 to 2000 years, the mechanisms that control atmospheric CH4 still remain unclear, partly because the late Holocene CH4 budget may be comprised of both natural and anthropogenic emissions. In contrast, the early Holocene was a period when human influence was substantially smaller, allowing us to elucidate more clearly the natural controls under interglacial conditions more clearly. Here we present new high-resolution CH4 records from Siple Dome, Antarctica, covering from 11.6 to 7.7 thousands of years before 1950 AD (ka). We observe four local CH4 minima on a roughly 1000-year spacing, which correspond to cool periods in Greenland. We hypothesize that the cooling in Greenland forced the Intertropical Convergence Zone (ITCZ) to migrate southward, reducing rainfall in northern tropical wetlands. The inter-polar difference (IPD) of CH4 shows a gradual increase from the onset of the Holocene to ∼ 9.5 ka, which implies growth of boreal source strength following the climate warming in the northern extratropics during that period.
Journal Article
Methane Emissions from Unique Wetlands in China
Methane Emissions from Unique Wetlands in China: Case Studies, Meta Analyses and Modelling is a landmark volume in the development of studies about methane emission from wetlands. Although there are books about methane emissions from rice paddies, natural wetlands and reservoirs, this book is the first one that provides information about methane emission from wetlands in China. Moreover, the book picks up very unique wetlands, alpine wetlands on the eastern edge of the Qinghai-Tibetan Plateau, and Three Gorges Reservoir (the world's largest hydroelectric reservoir) as cases to study methane emissions. It reviews and meta-analyses methane emissions from rice paddies, natural wetlands and lakes in China during the past twenty years. Furthermore, this book acts as bridge to connect microbial ecology and modelling: it both describes methane-producing bacteria dynamics and methane emission modelling.
eBook
Estimating emissions of methane consistent with atmospheric measurements of methane and δ13C of methane
We have constructed an atmospheric inversion framework based on TM5-4DVAR to jointly assimilate measurements of methane and δ13C of methane in order to estimate source-specific methane emissions. Here we present global emission estimates from this framework for the period 1999–2016. We assimilate a newly constructed, multi-agency database of CH4 and δ13C measurements. We find that traditional CH4-only atmospheric inversions are unlikely to estimate emissions consistent with atmospheric δ13C data, and assimilating δ13C data is necessary to derive emissions consistent with both measurements. Our framework attributes ca. 85 % of the post-2007 growth in atmospheric methane to microbial sources, with about half of that coming from the tropics between 23.5∘ N and 23.5∘ S. This contradicts the attribution of the recent growth in the methane budget of the Global Carbon Project (GCP). We find that the GCP attribution is only consistent with our top-down estimate in the absence of δ13C data. We find that at global and continental scales, δ13C data can separate microbial from fossil methane emissions much better than CH4 data alone, and at smaller scales this ability is limited by the current δ13C measurement coverage. Finally, we find that the largest uncertainty in using δ13C data to separate different methane source types comes from our knowledge of atmospheric chemistry, specifically the distribution of tropospheric chlorine and the isotopic discrimination of the methane sink.
Journal Article
Role of Megafauna and Frozen Soil in the Atmospheric CH4 Dynamics
Modern wetlands are the world's strongest methane source. But what was the role of this source in the past? An analysis of global 14C data for basal peat combined with modelling of wetland succession allowed us to reconstruct the dynamics of global wetland methane emission through time. These data show that the rise of atmospheric methane concentrations during the Pleistocene-Holocene transition was not connected with wetland expansion, but rather started substantially later, only 9 thousand years ago. Additionally, wetland expansion took place against the background of a decline in atmospheric methane concentration. The isotopic composition of methane varies according to source. Owing to ice sheet drilling programs past dynamics of atmospheric methane isotopic composition is now known. For example over the course of Pleistocene-Holocene transition atmospheric methane became depleted in the deuterium isotope, which indicated that the rise in methane concentrations was not connected with activation of the deuterium-rich gas clathrates. Modelling of the budget of the atmospheric methane and its isotopic composition allowed us to reconstruct the dynamics of all main methane sources. For the late Pleistocene, the largest methane source was megaherbivores, whose total biomass is estimated to have exceeded that of present-day humans and domestic animals. This corresponds with our independent estimates of herbivore density on the pastures of the late Pleistocene based on herbivore skeleton density in the permafrost. During deglaciation, the largest methane emissions originated from degrading frozen soils of the mammoth steppe biome. Methane from this source is unique, as it is depleted of all isotopes. We estimated that over the entire course of deglaciation (15,000 to 6,000 year before present), soils of the mammoth steppe released 300-550 Pg (10(15) g) of methane. From current study we conclude that the Late Quaternary Extinction significantly affected the global methane cycle.
Journal Article
The global methane budget 2000-2017
Understanding and quantifying the global methane (CH4) budget is important for assessing realistic pathways to mitigate climate change. Atmospheric emissions and concentrations of CH4 continue to increase, making CH4 the second most important human-influenced greenhouse gas in terms of climate forcing, after carbon dioxide (CO2). The relative importance of CH4 compared to CO2 depends on its shorter atmospheric lifetime, stronger warming potential, and variations in atmospheric growth rate over the past decade, the causes of which are still debated. Two major challenges in reducing uncertainties in the atmospheric growth rate arise from the variety of geographically overlapping CH4 sources and from the destruction of CH4 by short-lived hydroxyl radicals (OH). To address these challenges, 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)
Journal Article