nasa-gesdisc/es-publications-researchareas huggingface dataset:
Anthropogenic CO2 accumulation and uptake rates in the Pacific Ocean (2017)

AbstractThe anthropogenic CO2 accumulation rate for the Pacific Ocean was estimated from the decrease in 13C of the dissolved inorganic carbon measured on six World Ocean Circulation Experiment cruises during the 1990s and repeated during Climate Variability and Predictability in the 2000s. A mean depthintegrated anthropogenic 13C change of 83 20 m decade1 was estimated for the basin by using the multiple linear regression approach. The largest anthropogenic 13C decreases occurred between 40S and 60S, whereas the smallest decreases occurred in the Southern Ocean and subpolar North Pacific. A mean anthropogenic CO2 accumulation rate of 0.41 0.13 mol C m2 yr1 (0.82 0.26 Pg C yr1) was determined based on observed 13C changes and is in agreement with previous observation and modelbased estimates. The mean dissolved inorganic carbon DIC13 inventory change of 178 43 mol m2 decade1 was primarily the result of airsea CO2 exchange acting on the measured airsea 13C disequilibrium of ~ 1.2 0.1. Regional differences between the DIC13 inventory change and airsea 13CO2 flux yielded net anthropogenic CO2 uptake rates (independent of pCO2) that ranged from ~0 to 1 mol m2 yr1 and basinwide mean of 1.2 1.5 Pg C yr1. High rates of surface ocean DIC increase and 13C decrease observed in the Drake Passage (53S60S) support above average anthropogenic CO2 accumulation since 2005. Observed 13C changes in the Pacific Ocean indicate that ocean transport significantly impacted the anthropogenic CO2 distribution and illustrate the utility of 13C as a tracer to unravel the processes controlling the present and future accumulation of anthropogenic CO2 in the ocean.

Research areas: Greenhouse Gases
Agricultural Greenhouse Gas Emissions in a Data-Scarce Region Using a (2021)

Climate change may impact agricultural greenhouse gas emissions (GHGs) and yields under higher temperatures, higher atmospheric CO2 concentrations, and variable precipitations. This calls for adaptation strategies to optimize agricultural productions with minimal GHGs. This study aimed to identify these optimum agricultural managements in response to current and projected climatic scenarios for the Choctawhatchee Basin in Southeastern USA, an experimentally unexplored data-scarce region lacking validation data. This scenario-based modeling study analyzed a total of 1344 scenarios consisting of four major crops, eight managements (varying tillage, manuring, and residue), and forty climatic combinations under current as wells as two representative concentration pathways with process-based Denitrification and Decomposition (DNDC) model. The results indicated that the regions GHGs and yields were most affected by higher temperatures (+3 C) and extreme precipitation changes (40%), while high atmospheric CO2 concentrations exerted positive fertilization effects. The manure-related and higher residue incorporation scenarios were found to be better options in varying climates with minimal present global warming potentials (GWP) of 0.23 k to 29.1 k MT equivalent CO2. As such, the study presented climate change impacts and potential mitigation options in the study region while presenting a framework to design GHG mitigation in similar data-scarce regions.

Research areas: Greenhouse Gases
Assessing the impact of crops on regional CO2
                        fluxes and atmospheric concentrations (2010)

Human conversion of natural ecosystems to croplands modifies not only the exchange of water and energy between the surface and the atmosphere, but also carbon fluxes. To investigate the impacts of crops on carbon fluxes and resulting atmospheric CO<SUB>2</SUB> concentrations in the mid-continent region of the United States, we coupled a crop-specific phenology and physiology scheme for corn, soybean and wheat to the coupled ecosystem-atmosphere model SiB3-RAMS. Using SiBcrop-RAMS improved carbon fluxes at the local scale and had regional impacts, decreasing the spring uptake and increasing the summer uptake over the mid-continent. The altered fluxes changed the mid-continent atmospheric CO<SUB>2</SUB> concentration field at 120 m compared to simulations without crops: concentrations increased in May and decreased &gt;20 ppm during July and August, summer diurnal cycle amplitudes increased, synoptic variability correlations improved and the gradient across the mid-continent region increased. These effects combined to reduce the squared differences between the model and high-precision tower CO<SUB>2</SUB> concentrations by 20%. Synoptic transport of the large-scale N-S gradient caused significant day-to-day variability in concentration differences measured between the towers. This simulation study shows that carbon exchange between crops and the atmosphere significantly impacts regional CO<SUB>2</SUB> fluxes and concentrations.

Research areas: Greenhouse Gases
Large XCH<sub>4</sub> anomaly in summer 2013 over northeast Asia observed by GOSAT (2016)

Abstract. Extremely high levels of column-averaged dry-air mole fractions of atmospheric methane (XCH4) were detected in August and September 2013 over northeast Asia (  20 ppb above the averaged summertime XCH4 over 20092012, after removing a long-term trend), as being retrieved from the Short-Wavelength InfraRed (SWIR) spectral data observed with the Thermal And Near-infrared Sensor for carbon Observation  Fourier Transform Spectrometer (TANSO-FTS) onboard Greenhouse Gases Observing Satellite (GOSAT). Similar enhancements of XCH4 were also observed by the ground-based measurements at two Total Carbon Column Observing Network (TCCON) sites in Japan. The analysis of surface CH4 concentrations observed at three monitoring sites around the Japan archipelago suggest that the extreme increase of XCH4 has occurred in a limited area. The model analysis was conducted to investigate this anomalously high XCH4 event, using an atmospheric transport model. The results indicate that the extreme increase of XCH4 is attributed to the anomalous atmospheric pressure pattern over East Asia during the summer of 2013, which effectively transported the CH4-rich air to Japan from the strong CH4 source areas in east China. The two Japanese TCCON sites,   1000 km eastwest apart each other, coincidentally located along the substantially CH4-rich air flow from east China. This analysis demonstrates the capability of GOSAT to monitor an XCH4 event on a synoptic scale. We anticipate that the synoptic information of XCH4 from GOSAT data contributes to improve our understanding of regional carbon cycle and the regional flux estimation.

Research areas: Greenhouse Gases
Constraining global methane emissions and uptake by ecosystems (2011)

Abstract. Natural methane (CH4) emissions from wet ecosystems are an important part of today's global CH4 budget. Climate affects the exchange of CH4 between ecosystems and the atmosphere by influencing CH4 production, oxidation, and transport in the soil. The net CH4 exchange depends on ecosystem hydrology, soil and vegetation characteristics. Here, the LPJ-WHyMe global dynamical vegetation model is used to simulate global net CH4 emissions for different ecosystems: northern peatlands (4590 N), naturally inundated wetlands (60 S45 N), rice agriculture and wet mineral soils. Mineral soils are a potential CH4 sink, but can also be a source with the direction of the net exchange depending on soil moisture content. The geographical and seasonal distributions are evaluated against multi-dimensional atmospheric inversions for 20032005, using two independent four-dimensional variational assimilation systems. The atmospheric inversions are constrained by the atmospheric CH4 observations of the SCIAMACHY satellite instrument and global surface networks. Compared to LPJ-WHyMe the inversions result in a~significant reduction in the emissions from northern peatlands and suggest that LPJ-WHyMe maximum annual emissions peak about one month late. The inversions do not put strong constraints on the division of sources between inundated wetlands and wet mineral soils in the tropics. Based on the inversion results we diagnose model parameters in LPJ-WHyMe and simulate the surface exchange of CH4 over the period 19902008. Over the whole period we infer an increase of global ecosystem CH4 emissions of +1.11 Tg CH4 yr1, not considering potential additional changes in wetland extent. The increase in simulated CH4 emissions is attributed to enhanced soil respiration resulting from the observed rise in land temperature and in atmospheric carbon dioxide that were used as input. The long-term decline of the atmospheric CH4 growth rate from 1990 to 2006 cannot be fully explained with the simulated ecosystem emissions. However, these emissions show an increasing trend of +3.62 Tg CH4 yr1 over 20052008 which can partly explain the renewed increase in atmospheric CH4 concentration during recent years.

Research areas: Greenhouse Gases
Remote sensing northern lake methane ebullition (2020)

Northern lakes are considered a major source of atmospheric methane (CH4), a potent GHG1,2. However, large uncertainties in their emissions (726 Tg CH4 yr1; ref. 2) arise from challenges in upscaling field data, including fluxes by ebullition (bubbling), the dominant emission pathway2. Remote sensing of ebullition would allow detailed mapping of regional emissions but has hitherto not been developed. Here, we show that lake ebullition can be imaged using synthetic aperture radar remote sensing during ice-cover periods by exploiting the effect of ebullition on the texture of the icewater interface. Applying this method to five Alaska regions and combining spatial remote sensing information with year-round bubble-trap flux measurements, we create ebullition-flux maps for 5,143 Alaskan lakes. Regional lake CH4 emissions, based on satellite remote sensing analyses, were lower compared to previous estimates based on upscaling from individual lakes2,3 and were consistent with independent airborne CH4 observations. Thermokarst lakes formed by thaw of organic-rich permafrost had the highest fluxes, although lake density and lake size distributions also controlled regional emissions. This new remote sensing approach offers an opportunity to improve knowledge about Arctic CH4 fluxes and helps to explain long-standing discrepancies between estimates of CH4 emissions from atmospheric measurements and data upscaled from individual lakes.

Research areas: Greenhouse Gases
Influence of landscape management practices on urban greenhouse gas budgets (2021)

With a lack of United States federal policy to address climate change, cities, the private sector, and universities have shouldered much of the work to reduce carbon dioxide (CO2) and other greenhouse gas emissions. This study aims to determine how landcover characteristics influence the amount of carbon (C) sequestered and respired via biological processes, evaluating the role of land management on the overall C budget of an urban university. Boston University published a comprehensive Climate Action Plan in 2017 with the goal of achieving C neutrality by 2040. In this study, we digitized and discretized each of Boston Universitys three urban campuses into landcover types, with C sequestration and respiration rates measured and scaled to provide a University-wide estimate of biogenic C fluxes within the broader context of total University emissions.

Research areas: Greenhouse Gases
Multiple observation types reduce uncertainty in Australia's terrestrial carbon and water cycles (2013)

Abstract. Information about the carbon cycle potentially constrains the water cycle, and vice versa. This paper explores the utility of multiple observation sets to constrain a land surface model of Australian terrestrial carbon and water cycles, and the resulting mean carbon pools and fluxes, as well as their temporal and spatial variability. Observations include streamflow from 416 gauged catchments, measurements of evapotranspiration (ET) and net ecosystem production (NEP) from 12 eddy-flux sites, litterfall data, and data on carbon pools. By projecting residuals between observations and corresponding predictions onto uncertainty in model predictions at the continental scale, we find that eddy flux measurements provide a significantly tighter constraint on continental net primary production (NPP) than the other data types. Nonetheless, simultaneous constraint by multiple data types is important for mitigating bias from any single type. Four significant results emerging from the multiply-constrained model are that, for the 19902011 period: (i) on the Australian continent, a predominantly semi-arid region, over half the water loss through ET (0.64  0.05) occurs through soil evaporation and bypasses plants entirely; (ii) mean Australian NPP is quantified at 2.2  0.4 (1) Pg C yr1; (iii) annually cyclic ("grassy") vegetation and persistent ("woody") vegetation account for 0.67  0.14 and 0.33  0.14, respectively, of NPP across Australia; (iv) the average interannual variability of Australia's NEP (0.18 Pg C yr1, 1) is larger than Australia's total anthropogenic greenhouse gas emissions in 2011 (0.149 Pg C equivalent yr1), and is dominated by variability in desert and savanna regions.

Research areas: Ecosystems, Greenhouse Gases
Long-term variations of the mole fraction and carbon isotope ratio of atmospheric methane observed at Ny-Ålesund, Svalbard from 1996 to 2013 (2017)

We have conducted systematic observations of the CH4 mole fraction and its carbon isotope ratio (13C) at Ny-Alesund, Svalbard (7855N, 1156E) using air samples collected weekly since 1991 and 1996, respectively. The CH4 mole fraction showed long-term increase until 1999, stagnation between 2000 and 2006, followed by an increase after 2006. On the other hand, 13C showed monotonous increase until 2006 and decrease after 2006. By comparing the rates of change in the CH4 mole fraction and 13C under the assumption that the atmospheric CH4 lifetime is constant, it is suggested that the temporal pause of the CH4 mole fraction observed at Ny-Alesund is attributed to reductions of CH4 release from the microbial and fossil fuel sectors. On the other hand, the increase in CH4 after 2006 could be ascribed to an increase in microbial CH4 release. The CH4 and 13C data presented in this paper would be useful for clarifying their temporal variations in the Arctic atmosphere, as well as providing additional constraints on the global CH4 budget.

Research areas: Greenhouse Gases
How well can global chemistry models calculate the reactivity of short-lived greenhouse gases in the remote troposphere, knowing the chemical composition (2018)

Abstract. We develop a new protocol for merging in situ measurements with 3-D model simulations of atmospheric chemistry with the goal of integrating these data to identify the most reactive air parcels in terms of tropospheric production and loss of the greenhouse gases ozone and methane. Presupposing that we can accurately measure atmospheric composition, we examine whether models constrained by such measurements agree on the chemical budgets for ozone and methane. In applying our technique to a synthetic data stream of 14 880 parcels along 180 W, we are able to isolate the performance of the photochemical modules operating within their global chemistry-climate and chemistry-transport models, removing the effects of modules controlling tracer transport, emissions, and scavenging. Differences in reactivity across models are driven only by the chemical mechanism and the diurnal cycle of photolysis rates, which are driven in turn by temperature, water vapor, solar zenith angle, clouds, and possibly aerosols and overhead ozone, which are calculated in each model. We evaluate six global models and identify their differences and similarities in simulating the chemistry through a range of innovative diagnostics. All models agree that the more highly reactive parcels dominate the chemistry (e.g., the hottest 10 % of parcels control 2530 % of the total reactivities), but do not fully agree on which parcels comprise the top 10 %. Distinct differences in specific features occur, including the spatial regions of maximum ozone production and methane loss, as well as in the relationship between photolysis and these reactivities. Unique, possibly aberrant, features are identified for each model, providing a benchmark for photochemical module development. Among the six models tested here, three are almost indistinguishable based on the inherent variability caused by clouds, and thus we identify four, effectively distinct, chemical models. Based on this work, we suggest that water vapor differences in model simulations of past and future atmospheres may be a cause of the different evolution of tropospheric O3 and CH4, and lead to different chemistry-climate feedbacks across the models.

Research areas: Greenhouse Gases
Vista-LA: Mapping methane-emitting infrastructure in the Los Angeles megacity (2018)

Abstract. Methane (CH4) is a potent greenhouse gas (GHG) and a critical target of climate mitigation efforts. However, actionable emission reduction efforts are complicated by large uncertainties in the methane budget on relevant scales. Here, we present Vista, a Geographic Information System (GIS)-based approach to map potential methane emissions sources in the South Coast Air Basin (SoCAB) that encompasses Los Angeles, an area with a dense, complex mixture of methane sources. The goal of this work is to provide a database that, together with atmospheric observations, improves methane emissions estimates in urban areas with complex infrastructure. We aggregated methane source location information into three sectors (energy, agriculture, and waste) following the frameworks used by the State of California GHG Inventory and the Intergovernmental Panel on Climate Change (IPCC) Guidelines for GHG Reporting. Geospatial modeling was applied to publicly available datasets to precisely geolocate facilities and infrastructure comprising major anthropogenic methane source sectors. The final database, Vista-Los Angeles (Vista-LA), is presented as maps of infrastructure known or expected to emit CH4. Vista-LA contains over 33 000 features concentrated on < 1 % of land area in the region. Currently, Vista-LA is used as a planning and analysis tool for atmospheric measurement surveys of methane sources, particularly for airborne remote sensing, and methane hotspot detection using regional observations. This study represents a first step towards developing an accurate, spatially resolved methane flux estimate for point sources in SoCAB, with the potential to address discrepancies between bottomup and topdown methane emissions accounting in this region. The Vista-LA datasets and associated metadata are available from the Oak Ridge National Laboratory Distributed Active Archive Center for Biogeochemical Dynamics (ORNL DAAC; https://doi.org/10.3334/ORNLDAAC/1525).

Research areas: Greenhouse Gases
Carbon dioxide emissions from dry watercourses (2014)

Temporary watercourses that naturally cease to flow and run dry comprise a notable fraction of the worlds river networks, yet estimates of global carbon dioxide (CO2) emissions from watercourses do not consider emissions from these systems when they are dry. Using data from a sampling campaign in a Mediterranean river during the summer drought period, we demonstrate that the CO2 efflux from dry watercourses can be substantial, comparable to that from adjacent terrestrial soils and higher than from running or stagnant waters. With an up-scaling approach, we show that including emissions from dry watercourses could increase the estimate of CO2 emissions from watercourses in our study region by 0.615%. Moreover, our results tentatively illustrate that emissions from dry watercourses could be especially important in arid regions, increasing the estimate of global CO2 emissions from watercourses by 0.49%. Albeit relatively small, the contribution of dry watercourses could help to constrain the highly uncertain magnitude of the land carbon sink. We foresee that in many areas of the world, the expected increase in the extent of temporary watercourses associated with future global change will increase the relevance of CO2 emissions from dry watercourses.

Research areas: Greenhouse Gases
Informing urban climate planning with high resolution data: the Hestia fossil fuel CO2 emissions for Baltimore, Maryland (2020)

Cities contribute more than 70% of global anthropogenic carbon dioxide (CO2) emissions and are leading the effort to reduce greenhouse gas (GHG) emissions through sustainable planning and development. However, urban greenhouse gas mitigation often relies on self-reported emissions estimates that may be incomplete and unverifiable via atmospheric monitoring of GHGs. We present the Hestia Scope 1 fossil fuel CO2 (FFCO2) emissions for the city of Baltimore, Marylanda gridded annual and hourly emissions data product for 2010 through 2015 (Hestia-Baltimore v1.6). We also compare the Hestia-Baltimore emissions to overlapping Scope 1 FFCO2 emissions in Baltimores self-reported inventory for 2014.

Research areas: Greenhouse Gases
A high-resolution assessment on global nitrogen flows in cropland (2010)

Crop production is the single largest cause of human alteration of the global nitrogen cycle. We present a comprehensive assessment of global nitrogen flows in cropland for the year 2000 with a spatial resolution of 5 arc-minutes. We calculated a total nitrogen input (IN) of 136.60 trillion grams (Tg) of N per year, of which almost half is contributed by mineral nitrogen fertilizers, and a total nitrogen output (OUT) of 148.14 Tg of N per year, of which 55% is uptake by harvested crops and crop residues. We present high-resolution maps quantifying the spatial distribution of nitrogen IN and OUT flows, soil nitrogen balance, and surface nitrogen balance. The high-resolution data are aggregated at the national level on a per capita basis to assess nitrogen stress levels. The results show that almost 80% of African countries are confronted with nitrogen scarcity or nitrogen stress problems, which, along with poverty, cause food insecurity and malnutrition. The assessment also shows a global average nitrogen recovery rate of 59%, indicating that nearly two-fifths of nitrogen inputs are lost in ecosystems. More effective management of nitrogen is essential to reduce the deleterious environmental consequences.

Research areas: Agriculture
Ocean systems (2022)

The ocean comprises ~71% of the Earths surface area and is in constant interaction with the atmosphere above and the land surface at the coastal interface, allowing a continuous exchange of greenhouse gases (GHGs) between the spheres. The ocean plays an important role in absorbing and storing carbon dioxide (CO2) from fossil fuel combustion, land-use change, and cement production. Since the industrial revolution, the ocean has stored ~31% of human emitted CO2 adding to a total storage of anthropogenic CO2 of 15220PgC (PgC=Petagrams of carbon) from 1850 to 2007 and is currently removing about 2.60.6PgC of excess CO2 every year from the atmosphere. On longer timescales (i.e., centuries to millennia), the ocean carbon sink acts as a primary regulator of the Earths climate. While the ocean carbon sink mitigates climate change, absorption of anthropogenic CO2 leads to ocean acidification with potentially harmful effects for marine ecosystems. The ocean also contributes to the cycles of other greenhouse gases. Specifically, it is a weak source of methane. The contribution of the ocean to the net global methane budget, however, is substantially smaller than the oceanic uptake of CO2. The ocean was a net source of methane (CH4) to the atmosphere of ~13TgCH4year1 (TgCH4=Teragrams of CH4) with a possible range of 922TgCH4year1 over the period 200020. Hence, the methane fluxes from the ocean to the atmosphere are an order of magnitude smaller than the anthropogenic emissions over the same period. Likewise, the ocean comprises a natural source of nitrous oxide (N2O) of ~3.4TgNyear1between 2007 and 2016, although with a substantial possible range between 2.5 and 4.3TgNyear1.

Research areas: Greenhouse Gases