December 14-18, 2015
American Geophysical Union (AGU) Fall Meeting
San Francisco, California
International Center for Climate and Global Change Research in collaboration with researchers from Iowa State University, Emory Univerisy, National Institute of Environmental Studies are hosting a session on “Closing the Global Nitrous Oxide Budget: Magnitude, Spatiotemporal Patterns, and Responses” during AGU Fall Meeting 14-18 December, 2015. The poster session is scheduled on 14 December 2014 from 8:00-12:20, while the talk session is scheduled on 14 December 2015 from 16:00 – 18:00. To get more information about the presenters at these session please click the link below:
Beside the special session, several members from the International Center for Climate and Global Change Research giving a talk and poster presentation
Terrestrial uptake of carbon dioxide (CO2) partially mitigates global climate change induced by anthropogenic greenhouse (GHG) emissions. However, warming from increasing biogenic emissions of methane (CH4) and nitrous oxide (N2O) resulting from human activities may negate the cooling effect of CO2 uptake by the terrestrial biosphere. Terrestrial fluxes of individual GHGs have been studied intensively, but the net balance of the three major GHGs (CO2, CH4 and N2O) remains uncertain. Here we use bottom-up (BU: e.g., inventory, statistical extrapolation of local flux measurements, process-based modeling) and top-down (TD: atmospheric inversions) approaches to quantify net terrestrial biogenic fluxes of CO2, CH4 and N2O from natural ecosystems, croplands, and other biogenic sectors. After subtracting modeled estimates of pre-industrial fluxes from contemporary biogenic fluxes, we find the biogenic CH4 and N2O emissions resulting from human activities are opposite in sign but 1.6 times in magnitude equivalent to the global land uptake of CO2 in the 2000s based on global warming potential on 100-year time horizon. Among the emissions of CH4 and N2O, those from agriculture are the most important human perturbation, offsetting 1.2 to 1.4 times the global land CO2 sink. Our results suggest that the role of the terrestrial biosphere in exacerbating climate change could be alleviated if net human-induced biogenic GHG emissions were reduced through the implementation of land-based mitigation strategies, with the largest mitigation potential being in Southern Asia, a region that includes both China and India. This study highlights the importance of simultaneously considering three major GHGs in global and regional climate assessments, mitigation options and climate policy decisions, given the likely countervailing impacts of mitigation efforts, such as enhanced N2O emissions with soil C sequestration, paddy-drying to reduce CH4 emissions, and indirect emissions from biofuels.
As two most prevalent natural disturbances, drought and wildfire occur almost everywhere across the globe, and have been recognized as critical factors in modifying the terrestrial ecosystem structure and functioning. Although wildfires have been widely recognized to be associated with drought events, the combined impacts of droughts and fires on carbon and water cycles in terrestrial ecosystems have not yet been investigated well. To fill this knowledge gap, we examined the interactive impacts of drought and fire disturbances on the terrestrial ecosystem carbon and water cycles by synthesizing climate datasets, fire disturbance datasets, satellite observations, and ecosystem model simulations at both regional and global levels. Our results show that extreme droughts substantially reduced global ecosystem productivity, evapotranspiration, and river discharge. Meanwhile, fire events exacerbate the reductions in ecosystem productivity and carbon storage. Our preliminary results show that global fires reduced global net primary productivity of 4.14 Pg C year-1 during 1901-2010. Our study further indicates that climate warming in the recent decades induced more extreme drought and fire events, which have threatened the ecosystem capacities for sequestering carbon as well as providing freshwater over many regions of the world.
Nitrous oxide (N2O) is currently the third most important greenhouse gases (GHG) after methane (CH4) and carbon dioxide (CO2). Global N2O emission increased substantially primarily due to reactive nitrogen (N) enrichment through fossil fuel combustion, fertilizer production, and legume crop cultivation etc. In order to understand how climate system is perturbed by anthropogenic N2O emissions from the terrestrial biosphere, it is necessary to better estimate the pre-industrial N2O emissions. Previous estimations of natural N2O emissions from the terrestrial biosphere range from 3.3-9.0 Tg N2O-N yr?1. This large uncertainty in the estimation of pre-industrial N2O emissions from the terrestrial biosphere may be caused by uncertainty associated with key parameters such as maximum nitrification and denitrification rates, half-saturation coefficients of soil ammonium and nitrate, N fixation rate, and maximum N uptake rate. In addition to the large estimation range, previous studies did not provide an estimate on preindustrial N2O emissions at regional and biome levels. In this study, we applied a process-based coupled biogeochemical model to estimate the magnitude and spatial patterns of pre-industrial N2O fluxes at biome and continental scales as driven by multiple input data, including pre-industrial climate data, atmospheric CO2 concentration, N deposition, N fixation, and land cover types and distributions. Uncertainty associated with key parameters is also evaluated. Finally, we generate sector-based estimates of pre-industrial N2O emission, which provides a reference for assessing the climate forcing of anthropogenic N2O emission from the land biosphere.
Rice fields, supporting over half of the global population, consumed around 30% of the freshwater used for global crop growth and identified as one of the major methane (CH4) sources. Asia, in where 90% of rice is consumed, took over 90% of the total CH4 emission from the global rice field. With the increasing water scarcity and rapidly growth population, it is urgent to address how to simultaneously maintain or even increase food production, reduce water consumption, and benefit climate. In this study, we used a process-based model (Dynamic Land Ecosystem Model), which has the capability to simultaneously simulate the carbon, water, and nitrogen fluxes and storages within the terrestrial ecosystem, and also the exchanges of greenhouse gases between terrestrial ecosystems and the atmosphere, to quantify the magnitude, spatial and temporal variation of rice production and CH4 emissions under different water management practices. Simulated results have been evaluated against field observations, inventory-based and atmospheric inversion estimates. By implementing a set of experimental simulations, the results could provide insights for reasonable implementation of optimum water management practices, which is also crucial for policy maker to make trade-off decisions to increase yield and reduce GHG emissions through effective mitigation strategies.
The nexus approach to food, water and energy security in Asia is extremely important and relevant as the region has to feed two-third of the world’s population and accounts for 59% of the global water consumption. The distribution pattern of food, water and energy resources have been shaped by the legacy effect of both natural and anthropogenic disturbances and therefore are vulnerable to climate change and human activities including land use/cover change (LUCC) and land management (irrigation and nitrogen fertilization). In this study, we used the Dynamic Land Ecosystem Model (DLEM) to examine the effects of climate change, land use/cover change, and land management practices (irrigation and nitrogen fertilization) on the spatiotemporal trends and variability in water availability and its role in limiting net primary productivity (NPP) and food security in the 20th and early 21stcenturies. Our specific objectives are to quantify how climate change, LUCC and other environmental changes have interactively affected carbon and water dynamics across the Asian region. In particular, we separated the Asian region into several sub-region based on the primary limiting factor – water, food and energy. We then quantified how changes in environmental factors have altered the water and food resources during the past century. We particularly focused on Net Primary Productivity (NPP) and water cycle (Evapotranspiration, discharge, and runoff) as a measure of available food and water resources, respectively while understanding the linkage between food and water resources in Asia.
Last modified: October 18, 2015