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All Abstracts of Session BG04

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Oral Presentations

BG04 - Current Status of Terrestrial Carbon Budget and Process Understanding
Thursday, June 07, 2018 | 304B | 08:30-10:30
1.
BG04-D4-AM1-304B-001 (BG04-A004)
 
Current States of Terrestrial Carbon Budget Estimates
Masayuki KONDO1#+, Prabir PATRA2,3, Stephen SITCH4, Kazuhito ICHII1
1 Chiba University, Japan, 2 Japan Agency for Marine-Earth Science and Technology, Japan, 3 Tohoku University, Japan, 4 University of Exeter, United Kingdom
#Corresponding author: redmk92@gmail.com +Presenter

Terrestrial ecosystems play a critical role in formation of a feedback loop of carbon dioxide (CO2) in atmosphere by interacting with atmospheric reservoir and climate, and thus directing a course of the future projection of climate change. The research community has spent significant efforts to understand behaviors of terrestrial ecosystems under a steady rise in atmospheric CO2 concentration and temperature during the recent decades and deepen knowledge about the regional and global patterns of terrestrial CO2 sinks and sources with top-down and bottom-up modelling approaches (terrestrial biosphere and inverse models, respectively). However, the current estimates of terrestrial CO2 budgets by those approaches remain inconsistent. As illustrated in the recent IPCC Assessment Report (AR5), the inverse models tend to indicate stronger CO2 sinks in temperate and boreal regions than the biosphere models. Furthermore, the two modelling approaches exhibited contrasting CO2 sink–source patterns in the tropics; the biosphere models indicated weak CO2 sinks and the inverse models strong CO2 sources. As illustrated by these inconsistencies, a consensus on the geographic distribution of the terrestrial CO2 budgets has yet to be established among the research community.

To understand the current states of CO2 budget estimates and of reconciliation between the existing approaches, here we comprehensively compare global and regional CO2 budgets from the biosphere models from a comprehensive process model intercomparison (TRENDY) and the inversion models including results from the Asia-Pacific-Network (APN) intercompasion. We show an improved level of agreement between the two estimates in relation to regional and global budgets, since the IPCC AR5. We also discuss the remaining issues causing inconsistency between the two estimates.

2.
BG04-D4-AM1-304B-002 (BG04-A011)
 
Assessing Uncertainty in the Terrestrial Carbon Cycle: An Analysis of Historical Simulations with the Community Land Model
Gordon BONAN#+
National Center for Atmospheric Research, United States
#Corresponding author: bonan@ucar.edu +Presenter

The large spread among Earth system model terrestrial carbon cycle projections for the 21st century highlights divergent understanding of biological processes in the Earth system and is taken as an indicator of large uncertainty. Previous analysis found that model structure is the dominant source of uncertainty among CMIP5 models and showed the difficulty in reducing model uncertainty below scenario uncertainty, even when models are weighted based on their ability to reproduce the historical change in terrestrial carbon accumulation. Here, simulations for the historical period (1850-2010) with three generations of the Community Land Model (CLM4, CLM4.5, and CLM5) are used to investigate terrestrial carbon cycle uncertainty. The generational development of the CLM shows greater fidelity to many observationally-based datasets, and the iLAMB benchmarking analysis system quantifies the improvements in model performance across CLM4, CLM4.5, and CLM5. There is similar improved correspondence with estimates of the historical terrestrial carbon flux from the Global Carbon Project. Reconstruction of historical climate is the dominant source of uncertainty until the mid-20th century, after which model uncertainty dominates. Assessment of the quality of the carbon cycle simulations varies depending on the climate forcing used and the time period of the analysis. While the generational development of the CLM shows that model performance can be improved through better process representation, there is still much we do not know about the terrestrial carbon cycle and how to mathematically formulate biological processes at the global scale. It is likely that model uncertainty will remain high as more biology, with divergent understanding, is added to Earth system models.

3.
BG04-D4-AM1-304B-003 (BG04-A020)
 
Regional Changes in Land-Atmospheric CO2 Exchance over Recent Decades Using Trendy DGVMs
Stephen SITCH#, Anna HARPER+, Pierre FRIEDLINGSTEIN
University of Exeter, United Kingdom
#Corresponding author: s.a.sitch@exeter.ac.uk +Presenter

Land ecosystems currently moderate global climate change by absorbing over one quarter of the anthropogenic emissions of carbon dioxide (CO2) on average every year (Le Quéré et al., 2015). This CO2‘sink’ is modulated by climate change and variability. For the historical period, 1901-2016, we analyse outputs from a suite of Dynamic Global Vegetation Models (DGVMs), driven with observed climatology, to quantify the regional trends in CO2 and H2O fluxes. Trends will be attributed to underlying processes, i.e. climate variability and change, changes in atmospheric CO2 concentration, and land use and land cover changes (LULCC) (Sitch et al., 2015).

Here we use the DGVMs to quantify the global and regional mean, Interannual Variability (IAV) and trends in CO2 fluxes over the period 1990-2016, attribute to underlying processes, and quantify the uncertainty and level of model agreement. We will utilise ESA remote sensing data of land surface properties. Land cover data from the ESA-CCI-Land Cover project will be compared to land cover maps used in each DGVM model, and to land cover change currently used as an input to the TRENDY models. TRENDY simulations will also make use of the ESA-CCI-Soil moisture data until 2014 to evaluate the models. This is critical as soil moisture is one of the key drivers of land ecosystem productivity, soil decomposition, and hence the net carbon flux. In addition, burned areas from ESA-CCI-Fire will be used to evaluate TRENDY models with a dynamic fire model that internally simulate burned areas.

References

1.  Le Quéré et al., Global Carbon Budget 2014, Earth Syst. Sci. Data, 7, 47-85, doi:10.5194/essd-7-47-2015.

2.  Sitch, S, P. Friedlingstein, N. Gruber, S. Jones, G. Murray-Tortarolo, A. Ahlström, S. C. Doney, H. Graven, C. Heinze, C. Huntingford, S. Levis, P. E. Levy, M. Lomas, B. Poulter, N. Viovy, S. Zaehle, N. Zeng, A. Arneth, G. Bonan, L. Bopp, J. G. Canadell, F. Chevallier, P. Ciais, R. Ellis, M. Gloor, P. Peylin, S. Piao, C. Le Quéré, B. Smith, Z. Zhu, R. Myneni Trends and drivers of regional sources and sinks of carbon dioxide over the past two decades, Biogeosciences, 12, 653-679, 2015.

4.
BG04-D4-AM1-304B-004 (BG04-A021)
 
Does Improving Model Processes Lead to Better Constraints on Future Carbon Budgets?
Anna HARPER1#+, Karina WILLIAMS2, Chris HUNTINGFORD3, Anne VERHOEF4, Peter COX1, Pier VIDALE4
1 University of Exeter, United Kingdom, 2 UK Met Office, United Kingdom, 3 Centre for Ecology and Hydrology, United Kingdom, 4 University of Reading, United Kingdom
#Corresponding author: a.harper@exeter.ac.uk +Presenter

The response of the carbon cycle to future changes in climate, nutrient cycles, and land management practices is uncertain. The land carbon sink will play a relatively large role in whether or not low climate change targets (e.g. from the Paris climate agreement) are achievable, due to both natural processes and intentional land-management for greenhouse gas removal.

Recent studies based on model-data comparisons and model intercomparison projects have pointed out numerous uncertain processes in models, for example the effect of increased CO2 on vegetation, acclimation of photosynthesis and plant respiration, carbon-nitrogen cycles, and plant responses to elevated temperature and drought. Here we focus on the latter. Following a meeting of JULES modellers in 2016, it was determined that the impact of soil moisture stress on vegetation is a primary source of model uncertainty (JULES is the Joint UK Land Environment Simulator). Since then, a JULES process evaluation group (JPEG) has investigated new methods and parameterizations of soil moisture stress for JULES.

This presentation will cover some of the improvements resulting from the JPEG and explore their impacts on present day simulations and future carbon budgets. We use JULES coupled to IMOGEN, a simple climate emulator that allows JULES to be forced by a range of climate change patterns spanning the uncertainty present in the CMIP5 GCMs. Because JULES-IMOGEN is relatively computationally inexpensive, it can be used to run a series of sensitivity tests evaluating the role of soil moisture stress in the future land carbon sink. We will evaluate the impact of this specific improvement on the future land sink and on the range of uncertainty due to climate.

5.
BG04-D4-AM1-304B-005 (BG04-A013)
 
Evaluating Simulated Terrestrial Carbon Cycles by Earth System Models and Offline Models Using Data-Driven Estimations
Kazuhito ICHII1,2#+, Hiroaki TAKAYAMA3, Tomohiro HAJIMA3, Masayuki KONDO1, Prabir PATRA3,4, Kaoru TACHIIRI3
1 Chiba University, Japan, 2 National Institute for Environmental Studies, Japan, 3 Japan Agency for Marine-Earth Science and Technology, Japan, 4 Tohoku University, Japan
#Corresponding author: kazuhito.ichii@gmail.com +Presenter

Improvement of terrestrial submodels in earth system models (ESMs) is important to reduce uncertainties in future projections of global carbon cycle and climate. To test performances of terrestrial submodels, many studies from ESM communities evaluated terrestrial model outputs from ESMs. On the other hand, communities of offline terrestrial models, which run with observed climate data, also have evaluated using observation data. Therefore, evaluation of terrestrial models have been separately conducted by ESM community and offline model community. In this study, we evaluated the terrestrial outputs from ESMs and offline models with the latest observation based datasets. We used CMIP-5 outputs as ESM outputs, and TRENDY outputs as offline model outputs. As observation datasets, we used various satellite-based datasets, in particular, data-driven estimation of terrestrial CO2 and H2O fluxes. As a result, for example, regarding the gross primary productivity (GPP), model-by-model differences in offline models were smaller than those in ESMs. On the other hand, for net biome productivity (NBP), ESM outputs have less uncertainty than offline models. It might be because ESMs focus on the phenomenon on the global scale and is modeled so as to better match the change in CO2 concentration at global scale. On the other hand, with regard to the offline model, emphasis is placed on the reproducibility of individual processes, and it is considered that there are many variations among models as to global totals. From these results, we can expect model improvements by bringing advantages in both ESM and offline model.

6.
BG04-D4-AM1-304B-006 (BG04-A003)
 
Nonlinear Interactions Between Climate and Atmospheric Carbon Dioxide Drivers of Carbon Cycle Changes from 1850 to 2300
Forrest HOFFMAN1,2#+, James RANDERSON3, Keith LINDSAY4
1 Oak Ridge National Laboratory, United States, 2 University of Tennessee, Knoxville, United States, 3 University of California, Irvine, United States, 4 National Center for Atmospheric Research, United States
#Corresponding author: forrest@climatemodeling.org +Presenter

Quantifying feedbacks between the global carbon cycle and Earth's climate system is important for predicting future atmospheric CO2 levels and informing carbon management and energy policies. We applied a feedback analysis framework to three sets of Historical (1850–2005), Representative Concentration Pathway 8.5 (2006–2100), and its extension (2101–2300) simulations from the Community Earth System Model version 1.0 (CESM1(BGC)) to quantify drivers of terrestrial responses of carbon uptake. In the biogeochemically coupled simulation (BGC), the effects of CO2 fertilization and nitrogen deposition influenced marine and terrestrial carbon cycling. In the radiatively coupled simulation (RAD), the effects of rising temperature and circulation changes due to radiative forcing from CO2, other greenhouse gases, and aerosols were the sole drivers of carbon cycle changes. In the third, fully coupled simulation (FC), both the biogeochemical and radiative coupling effects acted simultaneously. We found that climate–carbon sensitivities derived from RAD simulations produced a net land carbon storage climate sensitivity that was stronger than those diagnosed from the FC and BGC simulations. For the land, this nonlinearity was associated with strong gains in gross primary production in the FC simulation, driven by enhancements in the hydrological cycle and increased nutrient availability. We developed and applied a nonlinearity metric to rank model responses and driver variables. The climate–carbon cycle feedback gain at 2300 was 42% higher when estimated from climate–carbon sensitivities derived from the difference between FC and BGC than when derived from RAD. These differences are important to quantify and understand because different model intercomparison efforts have used different approaches to compute feedbacks, complicating intercomparison of ESMs over time. Underestimating the climate–carbon cycle feedback gain would result in allowable emissions estimates that would be too low to meet climate change targets.

7.
BG04-D4-AM1-304B-007 (BG04-A007)
 
Continuity of Multi-Sensor Vegetation Index Data Records: A Case Study from MODIS to VIIRS
Tomoaki MIURA#+
University of Hawaii at Manoa, United States
#Corresponding author: tomoakim@hawaii.edu +Presenter

Vegetation index (VI) time series data derived from moderate resolution sensors such as Earth Observing System Moderate Resolution Imaging Spectroradiometer (MODIS) have widely been used to characterize seasonal and inter-annual dynamics of terrestrial vegetation photosynthetic activities, to identify “hot spot” areas of vegetation changes, and to scale-up in situ flux measurements at regional to global scales. The Visible Infrared Imaging Radiometer Suite (VIIRS) sensor series of the Joint Polar Satellite System program is slated to continue the highly calibrated data stream initiated with MODIS. In this study, cross-sensor compatibility of MODIS vs. VIIRS VI time series data were evaluated using one-year global data for year 2015. The objective of this study was to identify key parameters that would require an adjustment to generate a bias-free continuous time series dataset from MODIS and VIIRS. Three VIs, the “top-of-canopy (TOC)” normalized difference vegetation index (NDVI), TOC enhanced vegetation index (EVI), and TOC two-band enhanced vegetation index (EVI2), were investigated. For all the three VIs, MODIS and VIIRS VIs were subject to systematic differences in which VIIRS VIs were higher than the MODIS counterparts. Their overall systematic differences (measured as mean differences) and uncertainties (measured as root mean square differences) were however small, estimated as .010 - .020 VI units and .015 - .022 VI units, respectively. TOC NDVI cross-sensor differences were not seasonal- nor view zenith angle-dependent, whereas TOC EVI and TOC EVI2 cross-sensor differences were view zenith angle-dependent. Results of this study suggest that the normalization of view zenith angles is a required step to extend the MODIS VI record with VIIRS.

BG04 - Current Status of Terrestrial Carbon Budget and Process Understanding
Thursday, June 07, 2018 | 304B | 11:00-12:30
1.
BG04-D4-AM2-304B-008 (BG04-A001)
 
Carbon Balance of Tropical Peat Ecosystems in Southeast Asia
Takashi HIRANO1#+, Ryuichi HIRATA2, Kiwamu ISHIKURA1, Masayuki ITOH3, Ayaka SAKABE4, Frankie KIEW1, Guan Xhuan WONG1, Lulie MELLING5, Kitso KUSIN6
1 Hokkaido University, Japan, 2 National Institute for Environmental Studies, Japan, 3 Kyoto University, Japan, 4 Osaka Prefecture University, Japan, 5 Sarawak Tropical Peat Research Institute, Malaysia, 6 University of Palangkaraya, Indonesia
#Corresponding author: hirano@env.agr.hokudai.ac.jp +Presenter

Tropical peat swamp forest (PSF) is a unique ecosystem rich in carbon and water, which is widely distributed in Southeast Asia’s coastal lowlands, mainly in Indonesia and Malaysia. The ecosystem has accumulated a huge amount of organic carbon in peat soil over millennia under the condition of high groundwater level. However, the PSF has been reduced and degraded by logging, drainage and burning mainly because of land conversion to oil palm and pulp wood plantations during the last two decades. Such human disturbances potentially increase carbon dioxide (CO2) emissions to the atmosphere through enhanced oxidative peat decomposition and the increased risk of peat fires. Thus, tropical peatlands are recognized as a “hot spot” for vulnerable massive carbon pool in this century. It is very important to assess the current carbon status of tropical peatlands and quantify the effects of disturbance on the carbon balance to understand the role of tropical peatlands in the regional and global carbon balances. We have continuously measured ecosystem-scale eddy fluxes and soil fluxes of CO2 and methane (CH4) in different tropical peat ecosystems, including a little drained PSF, a drained PSF, a burned ex-PSF and an oil palm plantation, in Indonesia and Malaysia. Based on the monitoring data, I’ll talk about the carbon balance of tropical peat ecosystems, such as its seasonal variation and its relationship with groundwwater level, and the effect of disturbance due to human activities and management practices on the carbon balance.

2.
BG04-D4-AM2-304B-009 (BG04-A016)
 
ENSO Effects on the Terrestrial Carbon Cycle in the Tropics
Min XU1#+, Forrest HOFFMAN1,2, Paul LEVINE3, Nathan COLLIER1
1 Oak Ridge National Laboratory, United States, 2 University of Tennessee, Knoxville, United States, 3 University of California, Irvine, United States
#Corresponding author: minxu@climatemodeling.org +Presenter

The El Niño-Southern Oscillation (ENSO) strongly affects carbon cycle variations locally and globally by shifting climate regimes and variability through ocean-atmosphere interactions. The impacts of ENSO events on the terrestrial carbon cycle and its responses to ENSO-induced extremes, however, remain largely uncertain due to lack of observations and gaps in our understanding. In this study, we will use the US Department of Energy (DOE) Energy Exascale Earth System Model (E3SM) to study the effects of ENSO on the terrestrial carbon cycle in the tropics. We first compare the model results with satellite retrievals, in situ observations and global reanalysis data (i.e., CarbonTracker 2016, upscaled GPP data, etc.). Second, we study the changes in the carbon budget of the tropics among pre-, peri-, and post-ENSO events. Third, we evaluate the impacts of ENSO on the interannual variability of the atmospheric CO2 growth rate. Finally, we assess the carbon sensitivity to ENSO simulated by the model. Our results show that the variation of the carbon fluxes of the tropics are very sensitive to the ENSO-induced extremes and the simulated ENSO effects are generally consistent with the observations.

3.
BG04-D4-AM2-304B-010 (BG04-A012)
 
How Does Ecosystem Memory Impact the Terrestrial Carbon Balance During ENSO Events?
A. Anthony BLOOM1#+, Kevin BOWMAN1, Alexandra G. KONINGS2, Sassan SAATCHI1, John WORDEN1, Helen WORDEN3, Zhe JIANG3, Nicholas PARAZOO1, Mathew WILLIAMS4, David SCHIMEL1
1 Jet Propulsion Laboratory, California Institute of Technology, United States, 2 Stanford University, United States, 3 National Center for Atmospheric Research, United States, 4 University of Edinburgh, United Kingdom
#Corresponding author: abloom@jpl.nasa.gov +Presenter

The trajectory of the tropical carbon balance is in part regulated by the size and frequency of extreme weather events. Specifically, understanding the cumulative impact of ENSO events remains challenging, largely due to  uncertainties in the integrated response of carbon cycle processes to climate variability. Ultimately, an integrated understanding of both climate forcings and legacy effects (or “ecosystem memory”) on the terrestrial carbon balance is needed to understand the net impact of ENSO events on the tropical C balance. Here we use the CARbon DAta-MOdel fraMework (CARDAMOM) diagnostic model-data fusion approach – constrained by an array of C cycle satellite surface observations, including MODIS leaf area, biomass, OCO-2 and GOSAT solar-induced fluorescence, as well as “top-down” atmospheric inversion estimates of CO2 and CO surface fluxes from the NASA Carbon Monitoring System Flux (CMS-Flux) – to constrain and predict spatially-explicit tropical carbon state variables during 2010-2016. The combined assimilation of land surface and atmospheric datasets places key constraints on the temperature sensitivity and first order carbon-water feedbacks throughout the tropics and combustion factors within biomass burning regions. We show that across all tropical biomes, memory effects account for 30-50% of interannual flux variations; furthermore, we show that a quantitative disentanglement of direct forcing and memory effects is key for understanding the impact of individual ENSO events on the tropical C balance, and provides a critical constraint on the cumulative impact of ENSO events in future projections of the tropical C balance.

4.
BG04-D4-AM2-304B-011 (BG04-A005)
 
Quantifying the Effect of Changes in Climate-Driven Carbon Cycle Extremes and Land Use Change on the Terrestrial Carbon Budget Through Year 2300
Bharat SHARMA1#+, Forrest HOFFMAN2,3, Jitendra KUMAR2, Auroop R. GANGULY1
1 Northeastern University, United States, 2 Oak Ridge National Laboratory, United States, 3 University of Tennessee, Knoxville, United States
#Corresponding author: sharma.bha@husky.neu.edu +Presenter

The increasing concentration of atmospheric carbon dioxide and associated effects on the terrestrial biosphere have led to interest in understanding sources and sinks of carbon and biosphere feedbacks. The balance of terrestrial sources and sinks take up about a third of total anthropogenic emissions of CO2, which is modeled as net biosphere production (NBP). Any major climate perturbations or extreme events, such as droughts and heatwaves, have the potential to alter the terrestrial uptake strength, affecting total carbon budgets. Some studies have highlighted that a few spatiotemporal extreme events dominate the global carbon interannual variability. Recent studies have also found that, relative to the overall increase in global carbon uptake, the negative extremes in GPP and NEP would diminish towards the end of 21st century. A few studies have also highlighted that carbon loss due to land use and land cover change (LULCC), between 1850 and 2300, would be larger than the carbon loss due solely to the response of the biosphere to rising anthropogenic atmospheric greenhouse gases and aerosols.

Using results from the Community Earth Systems Model, we analyze the terrestrial carbon cycle extreme events when forced by the representative concentration pathway (RCP) 8.5 extended through the year 2300, in order to capture the non-linear feedbacks in global carbon cycle. The analysis focuses on global extreme events defined at the pixel level, and spatial-temporal contiguous dimensions. To investigate the role of anthropogenic forcing in modifying the extreme events, we consider the following scenarios: with and without anthropogenic atmospheric greenhouse gases and aerosols, and with and without LULCC. Our results provide insights into the contributions of humans in altering carbon cycle extremes, quantifies their growing implications for terrestrial carbon budgets, and can inform future mitigation policy.

5.
BG04-D4-AM2-304B-012 (BG04-A022)
 
Assessing the Impact of the 2015-2016 El Niño on Global Photosynthesis Using Satellite Remote Sensing
Xiangzhong LUO1#, Trevor KEENAN2+
1 Lawrence Berkeley National Laboratory, United States, 2 UC Berkeley, United States
#Corresponding author: xzluo@lbl.gov +Presenter

The El Niño-Southern Oscillation has a large influence on global climate regimes and on the global carbon cycle. Though El Niño is known to be associated with a reduction in the terrestrial carbon sink, results based on prognostic models or measurements disagree over the contributions of photosynthesis and respiration to the reduction. This study analyses five global remote sensing (RS) based gross primary productivity (GPP) products, along with solar-induced fluorescence from GOME-2, to provide a new stream of evidence for studying the impact of the 2015-2016 El Niño on terrestrial carbon uptake.

Our results demonstrate that an ensemble of RS GPP products shows an anomaly of -0.71 and 0.5 Peta-gram C in 2015 and 2016, respectively. RS GPP products show coherent anomalies over about half of the vegetated land surface, but they show large disagreement over the Amazon and tropical Asia. Croplands, shrubland and savanna show less inter-model variations than forests. The meteorological forcings for these RS GPP models demonstrate different patterns in the El Niño years, which partly explains the difference between RS GPP values. Focusing on the regions showing coherent RS GPP anomalies, we found that Africa plays a more important role than previously recognized in reducing GPP during the peak El Niño period and the Northern Hemisphere shows positive GPP anomalies in the late phase of El Niño.

BG04 - Current Status of Terrestrial Carbon Budget and Process Understanding
Thursday, June 07, 2018 | 304B | 13:30-15:30
1.
BG04-D4-PM1-304B-013 (BG04-A018)
 
Enhanced Terrestrial Carbon Uptake and the Role of CO2 Fertilization
Trevor KEENAN1#+, Colin PRENTICE2, Josep CANADELL3, Christopher WILLIAMS4, Han WANG5
1 UC Berkeley, United States, 2 Imperial College London, United Kingdom, 3 Commonwealth Scientific and Industrial Research Organisation, Australia, 4 Clarke University, United States, 5 Northwest A&F University, China
#Corresponding author: trevorkeenan@lbl.gov +Presenter

Terrestrial ecosystems play a significant role in the global carbon cycle and offset a large fraction of anthropogenic CO2 emissions. The terrestrial carbon sink is increasing, yet the mechanisms responsible for its enhancement, and implications for the growth rate of atmospheric CO2, remain unclear. Here, using global carbon budget estimates, ground, atmospheric and satellite observations, and multiple global vegetation models, we examine long-term changes in the terrestrial carbon cycle. We report a recent pause in the growth rate of atmospheric CO2, and a decline in the fraction of anthropogenic emissions that remain in the atmosphere, despite increasing anthropogenic emissions. We attribute the observed decline to increases in the terrestrial sink during the past decade, associated with the effects of rising atmospheric CO2 on vegetation and the slowdown in the rate of warming on global respiration. The pause in the atmospheric CO2 growth rate provides further evidence of the roles of CO2 fertilization and warming-induced respiration, and highlights the need to protect both existing carbon stocks and regions where the sink is growing rapidly.

3.
BG04-D4-PM1-304B-015 (BG04-A010)
 
Evaluations of Terrestrial Biogeochemical Feedbacks of Stratospheric Geoengineering Strategies
Cheng-En YANG1,2#+, Forrest HOFFMAN1,2, Simone TILMES3, Lili XIA4, Katie DAGON3, Joshua FU1, Jadwiga RICHTER3, Michael MILLS3, Ben KRAVITZ5, Douglas MACMARTIN6
1 University of Tennessee, Knoxville, United States, 2 Oak Ridge National Laboratory, United States, 3 National Center for Atmospheric Research, United States, 4 Rutgers University, United States, 5 Pacific Northwest National Laboratory, United States, 6 Cornell University, United States
#Corresponding author: cyang10@vols.utk.edu +Presenter

Stratospheric aerosol geoengineering options, involving injections of sulfur dioxide into the stratosphere, are being proposed to reduce the anthropogenic heating. While the impacts of stratospheric aerosol geoengineering on climate changes, such as stratospheric ozone depletion and weakened monsoons, have been extensively investigated in the past few decades, few studies have considered the biogeochemical responses and feedbacks on land resulting from such treatments. Previous Earth system model simulations incorporating stratospheric aerosol geoengineering scenarios primarily focused on the atmospheric radiative forcing and temperature response in the absence of biogeochemical feedbacks on land. Using the Stratospheric Aerosol Geoengineering Large Ensemble project model output (Tilmes et al., 2018), we evaluated the terrestrial carbon-nitrogen cycles and the hydrological cycle considering vegetation responses on land due to stratospheric aerosol geoengineering. Results of this analysis and implications for the terrestrial carbon cycle and hydrological cycle, as well as their impacts on the global carbon budget, will be presented.

Reference

Tilmes, S., J. H. Richter, M. J. Mills, B. Kravitz, D. MacMartin, I. Simpson, A. S. Glanville, J. Fasullo, et al. (2018): Strategic Stratospheric Aerosol Geoengineering Large Ensemble Project (GLENS). B. AM. METEOROL. SOC. (in preparation).

4.
BG04-D4-PM1-304B-016 (BG04-A009)
 
Parameter Optimization for Improvement of MODIS Gross Primary Production over East Asia
Haemi PARK#+, Jungho IM, Miae KIM
Ulsan National Institute of Science and Technology, South Korea
#Corresponding author: haemipark@unist.ac.kr +Presenter

The satellite-based GPP product is crucial to build and validate various environmental models as an input of carbon absorption. However, the accuracy of MOD17A2H especially in East Asia is still uncertain because of the coarse resolution of land cover and reanalysis meteorological dataset, and the consistent value to calculate light use efficiency (LUE) in MOD17 GPP algorithm. For that reason, the objective of this study is to improve the MOD17A2H GPP product by using a high resolution land cover map and the LUE parameter optimization. Target area is East Asia that includes Eastern China, Korean Peninsula, and Japan in extent of 30-48°N and 106-149°E. The LUEmax in Biome Property Look-Up-Table(BPLUT) was modified by the land cover percentage map of FROM-GLC at 30 m spatial resolution. The TMINmax and VPDmin which make the daily LUE saturate to 1 in the scalars are optimized using RMSE that the GPP compared with AsiaFlux database. Top and bottom 5-40% of TMIN and VPD, respectively, from Japanese 55-year Reanalysis (JRA55) on the flux tower site are tested refining TMINmax and VPDmin thresholds. As the result, the RMSE between optimized FROM-MCD GPP (FROM-MCD-opt) and flux tower GPP decreased than that of between MOD17A2H and flux tower from 21.83 (gC/m2/8days) to 16.11 (gC/m2/8days). The bias also diminished from –12.11 (gC/m2/8days) to –2.78. The results of area sum of annual GPP through climate classes and others were 973.75, 1377.79, and 1385.87 (gC/m2/yr) for MOD17A2H, FROM-MCD-opt, and BESS, respectively. Consequently, showing more positive agreement with the GPP of BESS and flux tower than the MOD17A2H, the improvement of MOD17A2H was successfully achieved in this study.

5.
BG04-D4-PM1-304B-017 (BG04-A002)
 
A Comparative Study on Anthropogenic Emission Inventory Development: Case Study Methane Emissions over China
Penwadee CHEEWAPHONGPHAN#+, Satoru CHATANI
National Institute for Environmental Studies, Japan
#Corresponding author: penwadee.chee@nies.go.jp +Presenter

‘2 degree Celsius’ under Paris Agreement, becomes a big challenge for all 171 (joint) countries to verify the responsibility on climate change problem. Nationally Determined Contributions (NDCs), a report under this agreement demonstrates inventory of greenhouse gas (GHG) emissions and the capability of country to mitigate GHG emissions. To ensure achievement of this target, the validation of NDCs report is necessary. There are several studies focus on inventory of methane (CH4), the short-lived climate pollutants, the second most important GHG, over Asia (especially China which is the major contributor) by using various tools even bottom up or top down approaches, that emission results demonstrate elevated discrepancies, criticizing on high uncertainty. The ambiguity of result between NDC and previous studies persuades to this study, in which aimed at to review and investigate the researches related on CH4 emission over China, identify the uncertainty among each research as well as the reason of the uncertainty, and examine the source of CH4 that take the largest uncertainty result. The study found the average amount of CH4 emission during the year 1990 to 2010 is in the range between 34,924 and 50,915 GgCH4yr-1, which the uncertainty is in the range of 3.4% to 51.3%, the lowest value estimated by bottom up – national scale method and the highest value estimated by bottom up – regional scale method.  Waste sector (MSW and wastewater) contributes the largest uncertainty for all studies, with the highest at more than 300% uncertainty whereas livestock (enteric fermentation and manure management) dominates the lowest uncertainty for all studies at the range between -26% and 12% which the lowest confidence comes from the result of national report.

Poster Presentations

  BG04-D3-PM1-P-018 (BG04-A006)
 
Implications of Overestimated Anthropogenic CO2 Emissions on East Asian and Global Land CO2 Flux Inversions
Tazu SAEKI1#+, Prabir PATRA2,3
1 National Institute for Environmental Studies, Japan, 2 Japan Agency for Marine-Earth Science and Technology, Japan, 3 Tohoku University, Japan
#Corresponding author: Saeki.tazu@nies.go.jp +Presenter

Measurement and modeling of regional or country-level carbon dioxide (CO2) fluxes are critical for verification of the greenhouse gases emission control. One of the commonly adopted approaches is inverse modeling, where CO2 fluxes from the terrestrial ecosystems are estimated by combining atmospheric CO2measurements with atmospheric transport models. The inverse models assume anthropogenic emissions are known, and thus an uncertainty in the emissions would introduce systematic bias in estimated terrestrial (residual) fluxes by inverse modeling. Here we show that the CO2 sink increase, estimated by inverse modelings, over East Asia (China, Japan, Korea and Mongolia) is likely an artifact of the a priori anthropogenic CO2 emissions. The residual CO2 sink increase by about 0.26 PgC yr-1 (1 Pg = 1015 g) during 2001-2010 is calculated as the fossil fuel (anthropogenic) emissions increased too quickly in China by 1.41 PgC yr-1. Independent results from methane (CH4) inversion suggested about 41% lower rate of East Asian CH4 emission increase during 2002-2012. We thus apply a scaling factor of 0.59, based on CH4 inversion, to the rate of anthropogenic CO2 emission increase. By doing that we find no systematic increase in land CO2 uptake over East Asia during 1993-2010 or 2000-2009. High bias in anthropogenic CO2 emissions also leads to stronger land sinks in global land-ocean flux partitioning in our inverse model. The corrected anthropogenic CO2 emissions by CH4 inversion results also produce measurable reductions in the rate of global land CO2 sink increase post-2002, leading to a better agreement with the terrestrial biospheric model simulations that include CO2-fertilization and climate effects.

  BG04-D3-PM1-P-019 (BG04-A008)
 
Plant Regrowth as a Driver of Recent Enhancement of Terrestrial Carbon Uptake
Masayuki KONDO1#+, Kazuhito ICHII1, Prabir PATRA2,3, Benjamin POULTER4, Leonardo CALLE5
1 Chiba University, Japan, 2 Japan Agency for Marine-Earth Science and Technology, Japan, 3 Tohoku University, Japan, 4 NASA Goddard Space Flight Center, United States, 5 Montana State University, United States
#Corresponding author: redmk92@gmail.com +Presenter

Attributing drivers of net carbon uptake in detail leads to clarification of causes for the recent enhancement of carbon dioxide (CO2) uptake by the terrestrial biosphere. The increasing strength of the land uptake in the 2000s has been attributed so far to a stimulating effect of rising atmospheric CO2 on photosynthesis (CO2 fertilization). However, it is still arguable whether the CO2 fertilization is a dominant cause for the recent enhancement of CO2 uptake because, in addition to the level of atmospheric CO2, the terrestrial biosphere has undergone historical changes through land use and management. CO2 emissions resulting from LUC activities account for ~9% of the total global anthropogenic CO2 emissions, therefore changes in LUC could affect the course of the net sink-source pattern of CO2 over time.

Here using an ensemble of biosphere models, we show a decadal-scale carbon uptake enhancement is induced not only by CO2 fertilization, but also an increasing uptake by plant regrowth from past land use changes (LUC), with its effect most pronounced in eastern North America, southern and eastern Europe, and southeastern temperate Eurasia. Our analysis indicates that ecosystems in North America and Europe have established the current productive state through regrowth over a half-century, and those in temperate Eurasia are still in a recovering stage from active LUC in the 1980s. As the strength of model representation of CO2 fertilization is still in debate, plant regrowth might have a greater potential to sequester carbon than indicated by this study.

  BG04-D3-PM1-P-020 (BG04-A014)
 
Teleconnection Based Terrestrial Carbon Cycle Forecasting and Attribution System
Benjamin POULTER1#, Lesley OTT1, Ashley BALLANTYNE2, Philippe CIAIS3, Ana BASTOS3, Abhishek CHATTERJEE4, Stephen SITCH5, Leonardo CALLE6+
1 National Aeronautics and Space Administration, United States, 2 University of Montana, United States, 3 Institut Pierre Simon Laplace, France, 4 NASA Goddard Space Flight Center, United States, 5 University of Exeter, United Kingdom, 6 Montana State University, United States
#Corresponding author: benjamin.poulter@nasa.gov +Presenter

Interannual variations in the atmospheric growth rate of carbon dioxide concentrations are driven primarily by terrestrial ecosystems, which respond on a relatively fast timescale to climate variability. Currently, dynamic global vegetation models (DGVM) are commonly used to diagnose the role of climate, land use, and carbon dioxide concentrations on the exchange of carbon between the land and atmosphere. DGVM models represent first-order processes that control carbon uptake, allocation, and release from ecosystems, but can be prone to high uncertainties and computational challenges related to acquiring forcing data with low latency. Here we present an empirical approach using climatic teleconnections to estimate net-carbon exchange between the land and atmosphere over the past 40 years and use the model to forecast carbon exchange on seasonal timescales. We use an ensemble of climatic teleconnections fitted against data from the TRENDY dynamic global vegetation model ensemble providing fluxes of net ecosystem exchange. The empirical model accounts for uncertainties and interactions between teleconnections and their temporal lags on a per-pixel basis for the past 40 years. Seasonal climate forecasts (one to seven month lead time) from the NASA Global Modeling and Assimilation Office Goddard Earth Observing System Model are used to forecast teleconnection phases, which are then used to predict net carbon uptake. The model is applied to explain recent terrestrial carbon uptake anomalies that occurred in 2011, 2014, and 2016, and is used to forecast the 2017 terrestrial land sink. Integrating process-based approaches and climatic teleconnections within empirical models can potentially allow for rapid assessment and interpretation of historical carbon uptake anomalies and to forecast seasonal.

  BG04-D3-PM1-P-021 (BG04-A015)
 
Detecting Vegetation Changes Induced by Afforestation in China Using Multiple Satellite Products
Kazuhito ICHII1,2#+, Yuji YANAGI3, Jingfeng XIAO4, Masayuki KONDO1
1 Chiba University, Japan, 2 National Institute for Environmental Studies, Japan, 3 Japan Agency for Marine-Earth Science and Technology, Japan, 4 University of New Hampshire, United States
#Corresponding author: kazuhito.ichii@gmail.com +Presenter

The use of multiple satellite-based data products can help analyze and understand changes in terrestrial vegetation cover and terrestrial CO2 cycles. Terrestrial vegetation environment in China is known as affected by many changes including both natural and anthropogenic changes. Especially, afforestation and land use change are considered as two of the most important factors. To date, satellite-based monitoring of terrestrial vegetation changes in China is conducted at either regional or country scales with coarse spatial resolutions. In this study, we analyzed vegetation changes in China from 2000 to 2015 using multiple satellite-based data products with higher spatial resolution. The products include ALOS PALSAR Forest/NonForest Map, LANDSAT based land cover map, MODIS land cover (MCD12Q1), vegetation continuous field (MOD44B) and vegetation index (MOD13A2). First, we assessed changes in forest cover from 2000 to 2015 using multiple forest cover products. We confirmed that two MODIS datasets, MCD12Q1 and MOD44B, were consistent with high resolution satellite based products (LANDSAT and ALOS PALSAR) and forest inventory with slight negative bias for MOD44B. The changes of forest cover by MCD12Q1 and MOD44B products were consistent, showing large increases in forest cover in central China, where afforestation were intensively conducted. Second, we analyzed temporal trends of vegetation index, and their dependency on land cover changes. Clear relations between temporal trends of vegetation index and land use change history were obtained; the highest increasing trends were observed in the grid cells where land use change from non-forest to forest occurred. These multiple pieces of evidence show that afforestation policy in China significantly affects forest areas and terrestrial vegetation for the 2000 to 2015 period.

  BG04-D3-PM1-P-022 (BG04-A017)
 
Global Terrestrial Carbon Budget Simulated by VISIT Model
Etsushi KATO#+
Institute of Applied Energy, Japan
#Corresponding author: e-kato@iae.or.jp +Presenter

Terrestrial sink and carbon uptake and losses affected by the anthropogenic land use and land-use change are the two largest components of the uncertainties in the evaluation of global carbon budget (Le Quéré et al. 2017). In this presentation, processes considered in the modelling of the terrestrial carbon budget by VISIT model are shown and how each component is affecting the calculated NBP. Also, sensitivity from land-use data (LUHv1 and LUHv2) is evaluated.

Reference

Le Quéré et al., 2017, Earth Syst. Sci. Data Discussions, https://doi.org/10.5194/essd-2017-123