At a Glance
The CMI methane project, initiated in spring 2017, consists of three interconnected subprojects: an experimental project dealing with the critical issue of methane releases from wetlands, and two modeling projects aimed at quantifying the sources, sinks, and variations of methane in the atmosphere and on land. All three projects are now in full swing, following the hiring of postdoctoral researchers during the second half of 2017.
1) The controls on methane release from wetlands
Wetlands are large and highly variable sources of the potent greenhouse gas methane. In these systems, methane emission to the atmosphere is shaped by a complex interplay of microbial, hydrological, and plant-associated processes, which vary in time and space. Contrary to the paradigm that microbial methane production is confined to oxygen-free habitats, recent research suggests that unsaturated soils and peats, containing significant levels of oxygen, may be important sources of methane. To understand the mechanisms underpinning this phenomenon, a group led by Xinning Zhang is studying how oxygen variability shapes carbon and nutrient transformation, community composition, and the activity of microbes important for methane cycling (Figure 1.9). Preliminary results indicate a potentially large enhancement of methane formation in wetlands subjected to cyclic variations in oxygen concentrations. Results will better constrain predictions of methane from high latitude ecosystems, where permafrost thaw is increasing the extent of wetlands and our understanding of methane cycling remains highly uncertain.
2) A global model of the atmospheric methane cycle.
Global atmospheric concentrations of methane started increasing in 2007 after a period of stabilization from 1999 to 2006. It has been challenging to attribute the changes in methane growth rate to specific sources or sinks of methane. A group led by Vaishali Naik is involved in developing and applying bottom-up global-scale chemistry climate models to better understand the processes that control the variability of atmospheric methane at decadal to centennial time scales. Initial tests show that the next-generation GFDL model, driven by historical emissions from the inventory developed for the Intercontinental Panel on Climate Change’s Sixth Assessment Report, is able to capture the observed variability and trends of the past 20 years. To facilitate the characterization of the drivers of methane variability and trends, the model is currently being advanced to include the representation of carbon and hydrogen isotopes of methane. Together with observations and model results, the group will be able to better quantify the roles of individual sources and sinks in driving methane variability.
3) A global model of the terrestrial methane cycle.
Quantification of past and future terrestrial sources and sinks of carbon requires a global comprehensive and high-resolution land model with enhanced ecological, biogeochemical, and hydrological capabilities, including prognostic methane emissions from natural and managed systems. The terrestrial component of GFDL’s new Earth System Model, LM4, includes a number of new capabilities and improvements, such as dynamic vegetation and carbon cycling, a representation of changing land-use practices, frozen soil dynamics, and a new vertically resolved soil biogeochemistry for carbon and nitrogen cycling. GFDL scientists, led by Elena Shevliakova, in collaboration with Princeton Environmental Institute researchers are implementing a new component characterizing explicitly soil microbes, which shape most soil biogeochemical cycles and control releases of the most potent greenhouses gases, carbon dioxide, and methane. The model captures wetland soil microbial processes, including growth and decomposition of microbes involved in methane production and oxidation. Methane is transported through aerobic layers of the soil column, where methanotrophic microbes oxidize part of the methane, and the rest escapes to the atmosphere.