Greenhouse Gases 3

Fire emissions of methane potentially represent a significant but highly uncertain component of the global methane budget with estimates ranging from 14 to 88 Tg / yr.  This range of estimates is driven in part by knowledge of dry matter burned, the fuel type, and variations in combustion efficiency. Here we use global estimates of CO emissions based on CO profiles from the NASA Terra MOPITT instrument and CH₄/CO emission ratios from NASA Aura TES data to constrain estimates of the global contribution to atmospheric methane from fires.  For the years 2001 to the present we find that fire emissions of methane are approximately 3% (or ~ 15 Tg / yr) of the global methane budget. Furthermore, fire emissions have likely been decreasing during this time period indicating that non-fire methane fluxes have primarily contributed to the recent increase in global atmospheric methane concentrations.

Biomass burning is one of the most important sources for atmospheric CO₂. The global annual emission of CO₂ from fires amounts to ~2 PgCyr^-1 which is about 25% of the anthropogenic fossil fuel emission (~8 PgCyr^-1). Despite the importance of the CO₂ emissions from fires for the carbon cycle, only few studies based directly on satellite CO₂ measurements have addressed to estimate fire CO₂ emissions. The main reason is that this is a challenging application as even large forest fires are expected to enhance the CO₂ column by only a few per mill due to the large background concentrations. In this context, the CARBOFIRES project aims at estimating CO₂ emissions from fires directly from satellite CO₂ measurements. This should be possible due to significantly improved satellite-based CO₂ data which have been obtained in the framework of ESA's GHG-CCI project. Here, first results of the CARBOFIRES project will be presented.

The ocean and atmosphere are major components of the Earth’s surface, with reactions within and between them controlling many of the properties of the Earth’s system.  The air-sea interface represents a vital link between the oceans and the atmosphere by acting as the conduit for the transfer of heat, momentum, aerosols, and gases between the two phases. In particular, the flux of gases such as oxygen, dimethyl sulfide, carbon dioxide (CO₂), and volatile iodocarbons across the interface is of fundamental importance to studies of marine productivity, biogeochemical cycles, atmospheric chemistry, Earth’s climate, and human health.

The ESA OceanFlux Greenhouse gases project was part of the ESA OceanFlux initiative and it focused primarily on interfacial transfer rates and thus upon gas concentrations on either side of the sea surface, and air-sea transfer coefficients.  The project took a multidisciplinary approach to the study and the work involved scientists from many different disciplines including Earth observation (microwave, optical, thermal infra-red and radar), modellers (ocean waves and ecosystems), physical oceanographers, marine carbonate scientists and computer scientists who specialize in “big data” storage and data processing.

We will firstly present a selection of the achievements from the first two-year (2011-2013) OceanFlux Greenhouse Gases project. These achievements include the successful synergistic use of model, in situ and satellite Earth observation data, the development of calibrated and validated algorithms for estimating gas transfer velocity from space (Goddijn-Murphy et al., 2012; 2013), the study of the CO₂ sink in Arctic waters (Land et al., 2013), the results of modelling the carbonate system in European shelf seas, the development of an open source gas flux processing toolbox (the FluxEngine) and methods for quantifying uncertainties in Earth observation derived air-sea gas fluxes and the first Earth observation derived global climatology of air-sea CO₂ gas fluxes (Goddijn-Murphy et al., 2015).  We will then present a selection of early results from the current 2 year phase (2014-2016) of the project, which will include an overview of our planned work on hurricanes and arctic waters, results from a recent global gas flux crowd-sourcing experiment and initial results from extending the FluxEngine toolbox to include support for nitrous oxide, dimethlysulphide and methane.

References:

Goddijn-Murphy, L. M., Woolf, D. K., Land, P. E., Shutler, J. D., and Donlon, C. (2015) The OceanFlux Greenhouse Gases methodology for deriving a sea surface climatology of CO2 fugacity in support of air–sea gas flux studies, Ocean Sci., 11, 519-541, doi:10.5194/os-11-519-2015.

Goddijn-Murphy, L., D. K. Woolf , B. Chapron and P. Queffeulou (2013) The enhancement of using dual-frequency, instead of single-frequency, altimeter backscatter for estimating air-sea gas transfer velocity, Remote Sensing of the Environment, 139. 1-5.

Goddijn-Murphy, L., D.K. Woolf and C.A. Marandino. (2012) Space-based retrievals of air-sea gas transfer velocities using altimeters: Calibration for dimethyl sulphide. Journal of Geophysical Research, 117, C08028, doi:10.1029/2011JC007535.

Land, P. E., J. D. Shutler, R. D. Cowling, D. K. Woolf, P. Walker, H. S. Findlay, R. C. Upstill-Goddard and C. J. Donlon (2013) Climate change impacts on sea–air fluxes of CO₂ in three Arctic seas: a sensitivity study using Earth observation, Biogeosciences, 10, 8109-8128.

One of the unanswered questions of climate change is how the biosphere uptake of carbon responds to events such as droughts and floods. Semi-arid regions have recently received interest as they respond more rapidly to these changing environmental conditions. Using the Greenhouse gases Observing SATellite (GOSAT) we have detected a large enhanced carbon sink over Australia from the end of 2010 until early 2012. This enhanced sink coincides with a strong La Nina event that led to record breaking precipitation over much of Australia. As a result of this precipitation, enhanced vegetation growth over much of the semi-arid regions of Australia occurred, which led to the aforementioned enhanced biosphere carbon uptake. Our findings show an anomaly in the carbon sink of roughly 0.8 Pg C yr^-1, which corresponds to 25 % of the multi-year annual average Gross Primary Production of the whole Australian biosphere. These results show the potential to monitor the carbon land sink in remote semi-arid regions, with satellites such as GOSAT.   

Droughts impact the carbon cycle by enhancing biomass burning, and by reducing the carbon uptake by the biosphere. Droughts are expected to increase under future climate change. Therefore a good understanding of the feedback processes between droughts and the carbon cycle is important for accurately predicting future carbon dioxide (CO₂) levels in the atmosphere. An important tracer for biomass burning is carbon monoxide (CO). By combining the information from both CO and CO₂ satellite data in an inverse modelling setup, it is possible to separately constrain the biomass burning and biosphere atmospheric fluxes of CO₂.

Within the TM5-4DVAR inverse modelling system, we implemented a joint CO-CO₂ inversion setup. The simulated CO and CO₂ concentrations were fully coupled, for instance by modelling the CO₂ production from oxidation of CO. The biomass burning CO emissions to the atmosphere are further constrained using satellite CO observations from IASI and MOPITT. We use available information on temporally and spatially varying CO:CO₂ emission ratios to calculate the direct biomass burning CO₂ flux based on derived CO emissions. The CO₂ exchange between the biosphere and atmosphere is then inferred using GOSAT satellite measurements.

Our inversion setup provides a powerful tool for investigating the ecosystem sensitivity to droughts. We will present first results of the coupled system, focusing on the regional effect of the 2010 drought event in Russia.