nasa-gesdisc/es-publications-researchareas huggingface dataset:
Carbon dioxide emission from drawdown areas of a Brazilian reservoir is linked to surrounding land cover (2019)

Reservoir sediments exposed to air due to water level fluctuations are strong sources of atmospheric carbon dioxide (CO2). The spatial variability of CO2 fluxes from these drawdown areas are still poorly understood. In a reservoir in southeastern Brazil, we investigated whether CO2 emissions from drawdown areas vary as a function of neighboring land cover types and assessed the magnitude of CO2 fluxes from drawdown areas in relation to nearby water surface. Exposed sediments near forestland (average = 2733 mg C m2 day1) emitted more CO2 than exposed sediments near grassland (average = 1261 mg C m2 day1), congruent with a difference in organic matter content between areas adjacent to forestland (average = 12.2%) and grassland (average = 10.9%). Moisture also had a significant effect on CO2 emission, with dry exposed sediments (average water content: 13.7%) emitting on average 2.5 times more CO2 than wet exposed sediments (average water content: 23.5%). We carried out a systematic comparison with data from the literature, which indicates that CO2 efflux from drawdown areas globally is about an order of magnitude higher than CO2 efflux from adjacent water surfaces, and within the range of CO2 efflux from terrestrial soils. Our findings suggest that emissions from exposed sediments may vary substantially in space, possibly related to organic matter supply from uphill vegetation, and that drawdown areas play a disproportionately important role in total reservoir CO2 emissions with respect to the area they cover.

Research areas: Greenhouse Gases
Water Security and Climate Change: Hydropower Reservoir Greenhouse Gas Emissions (2021)

Water storage is a driver for economic growth and often mentioned as a proxy for water securityWatersecurity. Hydropower storage projects deliver multiple benefits contributing to water and energy security; however, the reservoir creation raises concerns about greenhouse gas (GHG) emissions and puts in doubt how clean hydropower generation is. As storage becomes more relevant under climate changeClimatechange, adequate assessment is necessary to ensure projects sustainability. This study quantifies hydropower global median lifecycle greenhouse emissions at 23 gCO2e/kWh using the G-res Tool to estimate the net emission for 480 hydropower storage projects. This result is aligned with the IPCCIntergovernmental Panel on Climate Change (IPCC) estimates.

Research areas: Energy Production/Use
Aboveground live carbon stock changes of California wildland ecosystems, 2001–2010 (2015)

The balance between ecosystem emissions of carbon to the atmosphere and removals from the atmosphere indicates whether ecosystems are exacerbating or reducing climate change. Forest ecosystems in the State of California, USA, contain carbon that reaches the highest densities (mass per unit area) in the world, but it has been unresolved whether California ecosystems currently comprise a net sink or source of carbon. The California Global Warming Solutions Act of 2006 established greenhouse gas reduction targets for fossil fuel-burning sectors and ecosystems, underscoring the importance of tracking ecosystem carbon. Here, we conduct statewide spatial inventories of the aboveground live carbon stocks of forests and other terrestrial ecosystems of California, excluding agricultural and urban areas. We analyzed biomass data from field measurements of the Forest Inventory and Analysis program, published biomass information and remote sensing data on non-forest vegetation, and spatial distributions of vegetation types, height, and fractional cover derived by the Landfire program from Landsat remote sensing at 30m spatial resolution. We conducted Monte Carlo analyses of the uncertainty of carbon stock change estimates from errors in tree biomass estimates, remote sensing, and estimates of the carbon fraction of biomass. The carbon stock in aboveground biomass was 850230 Tg (mean95% confidence interval) in 2010. We found a net aboveground live carbon stock change of 6915 Tg from 2001 to 2010, a rate of change of 0.80.2%y1. Due to slow decay of some dead wood, all of the live carbon stock change does not immediately generate emissions. Wildfires on 6% of the state analysis area produced two-thirds of the live carbon stock loss. This suggests that increased tree densities from a century of fire suppression have allowed the accumulation of fuel for carbon losses in recent wildfires. Remote sensing errors in vegetation classification accounted for most of the uncertainty in the carbon stock change estimates. Improvements are also needed to track spatial patterns of growth and dead wood. Our results establish the beginning of a time series for the state greenhouse gas inventory and provide information on the role of forest conservation and management in California in mitigating global climate change.

Research areas: Greenhouse Gases
A multi-city urban atmospheric greenhouse gas measurement data synthesis (2022)

Urban regions emit a large fraction of anthropogenic emissions of greenhouse gases (GHG) such as carbon dioxide (CO2) and methane (CH4) that contribute to modern-day climate change. As such, a growing number of urban policymakers and stakeholders are adopting emission reduction targets and implementing policies to reach those targets. Over the past two decades research teams have established urban GHG monitoring networks to determine how much, where, and why a particular city emits GHGs, and to track changes in emissions over time. Coordination among these efforts has been limited, restricting the scope of analyses and insights. Here we present a harmonized data set synthesizing urban GHG observations from cities with monitoring networks across North America that will facilitate cross-city analyses and address scientific questions that are difficult to address in isolation.

Research areas: Greenhouse Gases
Increased greenhouse gas emissions intensity of major croplands in China: Implications for food security and climate change mitigation (2020)

AbstractBalancing crop production and greenhouse gas (GHG) emissions from agriculture soil requires a better understanding and quantification of crop GHG emissions intensity, a measure of GHG emissions per unit crop production. Here we conduct a stateoftheart estimate of the spatialtemporal variability of GHG emissions intensities for wheat, maize, and rice in China from 1949 to 2012 using an improved agricultural ecosystem model (Dynamic Land Ecosystem ModelAgriculture Version 2.0) and metaanalysis covering 172 fieldGHG emissions experiments. The results show that the GHG emissions intensities of these croplands from 1949 to 2012, on average, were 0.101.31 kg CO2eq/kg, with a significant increase rate of 1.843.58 103 kg CO2eq kg1 year1. Nitrogen fertilizer was the dominant factor contributing to the increase in GHG emissions intensity in northern China and increased its impact in southern China in the 2000s. Increasing GHG emissions intensity implies that excessive fertilizer failed to markedly stimulate crop yield increase in China but still exacerbated soil GHG emissions. This study found that overfertilization of more than 60% was mainly located in the winter wheatsummer maize rotation systems in the North China Plain, the winter wheatrice rotation systems in the middle and lower reaches of the Yangtze River and southwest China, and most of the double rice systems in the South. Our simulations suggest that roughly a onethird reduction in the current N fertilizer application level over these overfertilization regions would not significantly influence crop yield but decrease soil GHG emissions by 29.60%32.50% and GHG emissions intensity by 0.130.25 kg CO2eq/kg. This reduction is about 29% and 5% of total agricultural soil GHG emissions in China and the world, respectively. This study suggests that improving nitrogen use efficiency would be an effective strategy to mitigate GHG emissions and sustain China's food security.

Research areas: Greenhouse Gases
A global gridded (0.1× 0.1) inventory of methane emissions from oil, gas, and coal exploitation based on national reports to the United Nations Framework … (2020)

Abstract. Individual countries report national emissions of methane, a potent greenhouse gas, in accordance with the United Nations Framework Convention on Climate Change (UNFCCC). We present a global inventory of methane emissions from oil, gas, and coal exploitation that spatially allocates the national emissions reported to the UNFCCC (Scarpelli et al., 2019). Our inventory is at 0.10.1 resolution and resolves the subsectors of oil and gas exploitation, from upstream to downstream, and the different emission processes (leakage, venting, flaring). Global emissions for 2016 are 41.5 Tg a1 for oil, 24.4 Tg a1 for gas, and 31.3 Tg a1 for coal. An array of databases is used to spatially allocate national emissions to infrastructure, including wells, pipelines, oil refineries, gas processing plants, gas compressor stations, gas storage facilities, and coal mines. Gridded error estimates are provided in normal and lognormal forms based on emission factor uncertainties from the IPCC. Our inventory shows large differences with the EDGAR v4.3.2 global gridded inventory both at the national scale and in finer-scale spatial allocation. It shows good agreement with the gridded version of the United Kingdom's National Atmospheric Emissions Inventory (NAEI). There are significant errors on the 0.10.1 grid associated with the location and magnitude of large point sources, but these are smoothed out when averaging the inventory over a coarser grid. Use of our inventory as prior estimate in inverse analyses of atmospheric methane observations allows investigation of individual subsector contributions and can serve policy needs by evaluating the national emissions totals reported to the UNFCCC. Gridded data sets can be accessed at https://doi.org/10.7910/DVN/HH4EUM (Scarpelli et al., 2019).

Research areas: Energy Production/Use, Greenhouse Gases
The Importance of Lake Emergent Aquatic Vegetation for Estimating ArcticBoreal Methane Emissions (2022)

Areas of lakes that support emergent aquatic vegetation emit disproportionately more methane than open water but are under-represented in upscaled estimates of lake greenhouse gas emissions. These shallow areas are typically less than ∼1.5 m deep and can be detected with synthetic aperture radar (SAR). To assess the importance of lake emergent vegetation (LEV) zones to landscape-scale methane emissions, we combine airborne SAR mapping with field measurements of vegetated and open-water methane flux. First, we use Uninhabited Aerial Vehicle SAR data from the NASA Arctic-Boreal Vulnerability Experiment to map LEV in 4,572 lakes across four Arctic-boreal study areas and find it comprises ∼16% of lake area, exceeding previous estimates, and exhibiting strong regional differences (averaging 59 [50-68]%, 22 [20-25]%, 1.0 [0.8-1.2]%, and 7.0 [5.0-12]% of lake areas in the Peace-Athabasca Delta, Yukon Flats, and northern and southern Canadian Shield, respectively). Next, we account for these vegetated areas through a simple upscaling exercise using paired methane fluxes from regions of open water and LEV. After excluding vegetated areas that could be accounted for as wetlands, we find that inclusion of LEV increases overall lake emissions by 21 [18-25]% relative to estimates that do not differentiate lake zones. While LEV zones are proportionately greater in small lakes, this relationship is weak and varies regionally, underscoring the need for methane-relevant remote sensing measurements of lake zones and a consistent criterion for distinguishing wetlands. Finally, Arctic-boreal lake methane upscaling estimates can be improved with more measurements from all lake zones.

Research areas: Greenhouse Gases
Decadal Changes in Atmospheric Methane Emissions in the Eastern Himalayan Region: Source Apportionment and Impact Assessment (2022)

Methane (CH4), the second-largest greenhouse gas in terms of radiative forcing, is on the rise in the Eastern Himalayan region (EHR), as indicated by multiple datasets (CAMS ~ 0.087 Tg Yr1, EDGAR v4.3.2 ~ 0.11 Tg Yr1, and RCP8.5 ~ 0.16 Tg Yr1). We found that the CH4 trend over the EHR is stronger than the global trend due to increased emissions from anthropogenic sources. From 1990 to 2016, CH4 emissions from anthropogenic activities and wetlands increased by 20% and 10% over the EHR. The land-use land-cover (LULC)  change reveals a loss of ~ 0.42% of forest and an increase of 0.018% of urban built-up, 0.098% total wetland, and 0.033% of water-bodies coverage from 2001 to 2018. Future projections show a twofold (32.7 Tg CH4 Yr1) increase in CH4 emissions by 2050 and up to a threefold (~ 48.2 Tg CH4 Yr1) by the year 2100 from the base year level (14.6 Tg CH4 Yr1) in 2000. Ambient concentrations of CH4 measured in Dibrugarh and the CAMS reanalysis data set from March 2014 to February 2015 show the maximum in December (~ 4485 and ~ 1981 ppb, respectively), while the minimum concentrations in July (~ 1155 ppb and ~ 976 ppb). The calculated global/EHR RF due to the CH4 for 20062100 is higher (0.0093 Wm2 Yr1/0.0095 Wm2 Yr1) than the historical (0.0038 Wm2 Yr1/0.0037 Wm2 Yr1) during 18512005. The resultant land surface temperature increase induced solely by CH4 is higher over the EHR (~ 0.0062 C Yr1) than the global (~ 0.0036 C Yr1).

Research areas: Greenhouse Gases
Aircraft-based inversions quantify the importance of wetlands and livestock for Upper Midwest methane emissions (2021)

Abstract. We apply airborne measurements across three seasons (summer, winter and spring 20172018) in a multi-inversion framework to quantify methane emissions from the US Corn Belt and Upper Midwest, a key agricultural and wetland source region. Combing our seasonal results with prior fall values we find that wetlands are the largest regional methane source (32 %, 20 [1623] Gg/d), while livestock (enteric/manure; 25 %, 15 [1417] Gg/d) are the largest anthropogenic source. Natural gas/petroleum, waste/landfills, and coal mines collectively make up the remainder. Optimized fluxes improve model agreement with independent datasets within and beyond the study timeframe. Inversions reveal coherent and seasonally dependent spatial errors in the WetCHARTs ensemble mean wetland emissions, with an underestimate for the Prairie Pothole region but an overestimate for Great Lakes coastal wetlands. Wetland extent and emission temperature dependence have the largest influence on prediction accuracy; better representation of coupled soil temperaturehydrology effects is therefore needed. Our optimized regional livestock emissions agree well with the Gridded EPA estimates during spring (to within 7 %) but are  25 % higher during summer and winter. Spatial analysis further shows good top-down and bottom-up agreement for beef facilities (with mainly enteric emissions) but larger ( 30 %) seasonal discrepancies for dairies and hog farms (with > 40 % manure emissions). Findings thus support bottom-up enteric emission estimates but suggest errors for manure; we propose that the latter reflects inadequate treatment of management factors including field application. Overall, our results confirm the importance of intensive animal agriculture for regional methane emissions, implying substantial mitigation opportunities through improved management.

Research areas: Greenhouse Gases
Carbon dioxide sources from Alaska driven by increasing early winter respiration from Arctic tundra (2017)

Significance
            
              Rising arctic temperatures could mobilize reservoirs of soil organic carbon trapped in permafrost. We present the first quantitative evidence for large, regional-scale early winter respiration flux, which more than offsets carbon uptake in summer in the Arctic. Data from the National Oceanic and Atmospheric Administrations Barrow station indicate that October through December emissions of CO
              2
              from surrounding tundra increased by 73% since 1975, supporting the view that rising temperatures have made Arctic ecosystems a net source of CO
              2
              . It has been known for over 50 y that tundra soils remain unfrozen and biologically active in early winter, yet many Earth System Models do not correctly represent this phenomenon or the associated CO
              2
              emissions, and hence they underestimate current, and likely future, CO
              2
              emissions under climate change.
            
          , 
            
              High-latitude ecosystems have the capacity to release large amounts of carbon dioxide (CO
              2
              ) to the atmosphere in response to increasing temperatures, representing a potentially significant positive feedback within the climate system. Here, we combine aircraft and tower observations of atmospheric CO
              2
              with remote sensing data and meteorological products to derive temporally and spatially resolved year-round CO
              2
              fluxes across Alaska during 20122014. We find that tundra ecosystems were a net source of CO
              2
              to the atmosphere annually, with especially high rates of respiration during early winter (October through December). Long-term records at Barrow, AK, suggest that CO
              2
              emission rates from North Slope tundra have increased during the October through December period by 73%  11% since 1975, and are correlated with rising summer temperatures. Together, these results imply increasing early winter respiration and net annual emission of CO
              2
              in Alaska, in response to climate warming. Our results provide evidence that the decadal-scale increase in the amplitude of the CO
              2
              seasonal cycle may be linked with increasing biogenic emissions in the Arctic, following the growing season. Early winter respiration was not well simulated by the Earth System Models used to forecast future carbon fluxes in recent climate assessments. Therefore, these assessments may underestimate the carbon release from Arctic soils in response to a warming climate.

Research areas: Greenhouse Gases
Airborne mapping reveals emergent power law of arctic methane emissions (2020)

Methane (CH<SUB>4</SUB>) emissions from thawing permafrost amplify a climate warming feedback. However, upscaling of site-level CH<SUB>4</SUB> observations across diverse Arctic landscapes remains highly uncertain, compromising accuracy of current pan-Arctic CH<SUB>4</SUB> budgets and confidence in model forecasts. We report a 30,000-km<SUP>2</SUP> survey at 25-m<SUP>2</SUP> resolution (~1 billion observations) of CH<SUB>4</SUB> hotspot patterns across Alaska and northwestern Canada using airborne imaging spectroscopy. Hotspots covered 0.2% of the surveyed area, concentrated in the wetland-upland ecotone, and followed a two-component power law as a function of distance from standing water. Hotspots decreased sharply over the first 40 m from standing water (y = 0.21×<SUP>-0.649</SUP>, R<SUP>2</SUP> = 0.97), mirroring in situ flux observations. Beyond 40 m, CH<SUB>4</SUB> hotspots diminished gradually over hundreds of meters (y = 0.004×<SUP>-0.164</SUP>, R<SUP>2</SUP> = 0.99). This emergent property quantifies the distribution of strong methanogenic zones from site to regional scales, vastly improving metrics for scaling ground-based CH<SUB>4</SUB> inventories and validation of land models.

Research areas: Greenhouse Gases
Marine methane cycle simulations for the period of early global warming (2011)

Geochemical environments, fates, and effects are modeled for methane released into seawater by the decomposition of climate-sensitive clathrates. A contemporary global background cycle is first constructed, within the framework of the Parallel Ocean Program. Input from organics in the upper thermocline is related to oxygen levels, and microbial consumption is parameterized from available rate measurements. Seepage into bottom layers is then superimposed, representing typical seabed fluid flow. The resulting CH<SUB>4</SUB> distribution is validated against surface saturation ratios, vertical sections, and slope plume studies. Injections of clathrate-derived methane are explored by distributing a small number of point sources around the Arctic continental shelf, where stocks are extensive and susceptible to instability during the first few decades of global warming. Isolated bottom cells are assigned dissolved gas fluxes from porous-media simulation. Given the present bulk removal pattern, methane does not penetrate far from emission sites. Accumulated effects, however, spread to the regional scale following the modeled current system. Both hypoxification and acidification are documented. Sensitivity studies illustrate a potential for material restrictions to broaden the perturbations, since methanotrophic consumers require nutrients and trace metals. When such factors are considered, methane buildup within the Arctic basin is enhanced. However, freshened polar surface waters act as a barrier to atmospheric transfer, diverting products into the deep return flow. Uncertainties in the logic and calculations are enumerated including those inherent in high-latitude clathrate abundance, buoyant effluent rise through the column, representation of the general circulation, and bacterial growth kinetics.

Research areas: Greenhouse Gases
Lower-tropospheric CO2 from near-infrared ACOS-GOSAT observations (2017)

Abstract. We present two new products from near-infrared Greenhouse Gases Observing Satellite (GOSAT) observations: lowermost tropospheric (LMT, from 0 to 2.5 km) and upper troposphericstratospheric (U, above 2.5 km) carbon dioxide partial column mixing ratios. We compare these new products to aircraft profiles and remote surface flask measurements and find that the seasonal and year-to-year variations in the new partial column mixing ratios significantly improve upon the Atmospheric CO2 Observations from Space (ACOS) and GOSAT (ACOS-GOSAT) initial guess and/or a priori, with distinct patterns in the LMT and U seasonal cycles that match validation data. For land monthly averages, we find errors of 1.9, 0.7, and 0.8 ppm for retrieved GOSAT LMT, U, and XCO2; for ocean monthly averages, we find errors of 0.7, 0.5, and 0.5 ppm for retrieved GOSAT LMT, U, and XCO2. In the southern hemispheric biomass burning season, the new partial columns show similar patterns to MODIS fire maps and MOPITT multispectral CO for both vertical levels, despite a flat ACOS-GOSAT prior, and a COCO2 emission factor comparable to published values. The difference of LMT and U, useful for evaluation of model transport error, has also been validated with a monthly average error of 0.8 (1.4) ppm for ocean (land). LMT is more locally influenced than U, meaning that local fluxes can now be better separated from CO2 transported from far away.

Research areas: Greenhouse Gases