Quantifying the role of cold season processes in vegetation-permafrost feedbacks – WINTERPROOF

• Watts, Jennifer D.; Farina, Mary; Kimball, John S.; Schiferl, Luke D.; Liu, Zhihua & Arndt, Kyle A. [Show all 38 contributors for this article] (2023). Carbon uptake in Eurasian boreal forests dominates the high-latitude net ecosystem carbon budget. Global Change Biology. ISSN 1354-1013. 29(7), p. 1870–1889. doi: 10.1111/gcb.16553.
• Tømmervik, Hans; Julitta, Tommaso; Nilsen, Lennart; Park, Taejin; Burkart, Andreas & Ostapowicz, Katarzyna Anna [Show all 10 contributors for this article] (2023). The northernmost hyperspectral FLoX sensor dataset for monitoring of high-Arctic tundra vegetation phenology and Sun-Induced Fluorescence (SIF). Data in Brief. ISSN 2352-3409. 50. doi: 10.1016/j.dib.2023.109581. Full text in Research Archive Show summary

  A hyperspectral field sensor (FloX) was installed in Adventdalen (Svalbard, Norway) in 2019 as part of the Svalbard Integrated Arctic Earth Observing System (SIOS) for monitoring vegetation phenology and Sun-Induced Chlorophyll Fluorescence (SIF) of high-Arctic tundra. This northernmost hyperspectral sensor is located within the footprint of a tower for long-term eddy covariance flux measurements and is an integral part of an automatic environmental monitoring system on Svalbard (AsMovEn), which is also a part of SIOS. One of the measurements that this hyperspectral instrument can capture is SIF, which serves as a proxy of gross primary production (GPP) and carbon flux rates. This paper presents an overview of the data collection and processing, and the 4-year (2019–2021) datasets in processed format are available at: https://thredds.met.no/thredds/catalog/arcticdata/infranor/NINA-FLOX/raw/catalog.html associated with https://doi.org/10.21343/ZDM7-JD72 under a CC-BY-4.0 license. Results obtained from the first three years in operation showed interannual variation in SIF and other spectral vegetation indices including MERIS Terrestrial Chlorophyll Index (MTCI), EVI and NDVI. Synergistic uses of the measurements from this northernmost hyperspectral FLoX sensor, in conjunction with other monitoring systems, will advance our understanding of how tundra vegetation responds to changing climate and the resulting implications on carbon and energy balance. Chlorophyll fluorescenceSolar Induced Fluorescence (SIF)ReflectancePhotosynthetic functionMERIS terrestrial chlorophyll index (MTCI)High-Arctic tundra

• Lambert, Marius; Tang, Hui; Aas, Kjetil Schanke; Stordal, Frode; Fisher, Rosie & Bjerke, Jarle Werner [Show all 8 contributors for this article] (2023). Integration of a Frost Mortality Scheme Into the Demographic Vegetation Model FATES. Journal of Advances in Modeling Earth Systems. ISSN 1942-2466. 15(7). doi: 10.1029/2022MS003333. Full text in Research Archive
• Euskirchen, Eugénie S.; Bruhwiler, Lori M.; Commane, Róisín; Parmentier, Frans-Jan W.; Schädel, Christina & Schuur, Edward A. G. [Show all 7 contributors for this article] (2022). Current knowledge and uncertainties associated with the Arctic greenhouse gas budget. In Poulter, Benjamin; Canadell, Josep G.; Hayes, Daniel J. & Thompson, Rona Louise (Ed.), Balancing Greenhouse Gas Budgets. Accounting for Natural and Anthropogenic Flows of CO2 and other Trace Gases. Elsevier. ISSN 9780128149522. p. 159–201. doi: 10.1016/B978-0-12-814952-2.00007-1.
• Oehri, Jacqueline; Schaepman-Strub, Gabriela; Kim, Jin-Soo; Grysko, Raleigh; Kropp, Heather & Grünberg, Inge [Show all 74 contributors for this article] (2022). Vegetation type is an important predictor of the arctic summer land surface energy budget. Nature Communications. ISSN 2041-1723. 13. doi: 10.1038/s41467-022-34049-3. Full text in Research Archive
• Lambert, Marius; Tang, Hui; Aas, Kjetil Schanke; Stordal, Frode; Fisher, Rosie & Fang, Yilin [Show all 8 contributors for this article] (2022). Inclusion of a cold hardening scheme to represent frost tolerance is essential to model realistic plant hydraulics in the Arctic-boreal zone in CLM5.0-FATES-Hydro. Geoscientific Model Development. ISSN 1991-959X. 15(23), p. 8809–8829. doi: 10.5194/gmd-15-8809-2022. Full text in Research Archive Show summary

  As temperatures decrease in autumn, vegetation of temperate and boreal ecosystems increases its tolerance to freezing. This process, known as hardening, results in a set of physiological changes at the molecular level that initiate modifications of cell membrane composition and the synthesis of anti-freeze proteins. Together with the freezing of extracellular water, anti-freeze proteins reduce plant water potentials and xylem conductivity. To represent the responses of vegetation to climate change, land surface schemes increasingly employ “hydrodynamic” models that represent the explicit fluxes of water from soil and through plants. The functioning of such schemes under frozen soil conditions, however, is poorly understood. Nonetheless, hydraulic processes are of major importance in the dynamics of these systems, which can suffer from, e.g., winter “frost drought” events. In this study, we implement a scheme that represents hardening into CLM5.0-FATES-Hydro. FATES-Hydro is a plant hydrodynamics module in FATES, a cohort model of vegetation physiology, growth, and dynamics hosted in CLM5.0. We find that, in frozen systems, it is necessary to introduce reductions in plant water loss associated with hardening to prevent winter desiccation. This work makes it possible to use CLM5.0-FATES-Hydro to model realistic impacts from frost droughts on vegetation growth and photosynthesis, leading to more reliable projections of how northern ecosystems respond to climate change.

• Virkkala, Anna-Maria; Natali, Susan M.; Rogers, Brendan M.; Watts, Jennifer D.; Savage, Kathleen & Connon, Sara June [Show all 64 contributors for this article] (2022). The ABCflux database: Arctic–boreal CO2 flux observations and ancillary information aggregated to monthly time steps across terrestrial ecosystems. Earth System Science Data. ISSN 1866-3508. 14(1), p. 179–208. doi: 10.5194/essd-14-179-2022. Full text in Research Archive Show summary

  Past efforts to synthesize and quantify the magnitude and change in carbon dioxide (CO2) fluxes in terrestrial ecosystems across the rapidly warming Arctic–boreal zone (ABZ) have provided valuable information but were limited in their geographical and temporal coverage. Furthermore, these efforts have been based on data aggregated over varying time periods, often with only minimal site ancillary data, thus limiting their potential to be used in large-scale carbon budget assessments. To bridge these gaps, we developed a standardized monthly database of Arctic–boreal CO2 fluxes (ABCflux) that aggregates in situ measurements of terrestrial net ecosystem CO2 exchange and its derived partitioned component fluxes: gross primary productivity and ecosystem respiration. The data span from 1989 to 2020 with over 70 supporting variables that describe key site conditions (e.g., vegetation and disturbance type), micrometeorological and environmental measurements (e.g., air and soil temperatures), and flux measurement techniques. Here, we describe these variables, the spatial and temporal distribution of observations, the main strengths and limitations of the database, and the potential research opportunities it enables. In total, ABCflux includes 244 sites and 6309 monthly observations; 136 sites and 2217 monthly observations represent tundra, and 108 sites and 4092 observations represent the boreal biome. The database includes fluxes estimated with chamber (19 % of the monthly observations), snow diffusion (3 %) and eddy covariance (78 %) techniques. The largest number of observations were collected during the climatological summer (June–August; 32 %), and fewer observations were available for autumn (September–October; 25 %), winter (December–February; 18 %), and spring (March–May; 25 %). ABCflux can be used in a wide array of empirical, remote sensing and modeling studies to improve understanding of the regional and temporal variability in CO2 fluxes and to better estimate the terrestrial ABZ CO2 budget. ABCflux is openly and freely available online (Virkkala et al., 2021b, https://doi.org/10.3334/ORNLDAAC/1934).

• Helbig, M.; Živković, T.; Alekseychik, P.; Aurela, M.; El-Madany, T. S. & Euskirchen, E. S. [Show all 33 contributors for this article] (2022). Warming response of peatland CO2 sink is sensitive to seasonality in warming trends. Nature Climate Change. ISSN 1758-678X. 12, p. 743–749. doi: 10.1038/s41558-022-01428-z. Show summary

  Peatlands have acted as net CO2 sinks over millennia, exerting a global climate cooling effect. Rapid warming at northern latitudes, where peatlands are abundant, can disturb their CO2 sink function. Here we show that sensitivity of peatland net CO2 exchange to warming changes in sign and magnitude across seasons, resulting in complex net CO2 sink responses. We use multiannual net CO2 exchange observations from 20 northern peatlands to show that warmer early summers are linked to increased net CO2 uptake, while warmer late summers lead to decreased net CO2 uptake. Thus, net CO2 sinks of peatlands in regions experiencing early summer warming, such as central Siberia, are more likely to persist under warmer climate conditions than are those in other regions. Our results will be useful to improve the design of future warming experiments and to better interpret large-scale trends in peatland net CO2 uptake over the coming few decades.

• Parmentier, Frans-Jan W.; Nilsen, Lennart; Tømmervik, Hans & Cooper, Elisabeth J. (2021). A distributed time-lapse camera network to track vegetation phenology with high temporal detail and at varying scales. Earth System Science Data. ISSN 1866-3508. 13(7), p. 3593–3606. doi: 10.5194/essd-13-3593-2021. Full text in Research Archive Show summary

  Near-surface remote sensing techniques are essential monitoring tools to provide spatial and temporal resolutions beyond the capabilities of orbital methods. This high level of detail is especially helpful to monitor specific plant communities and to accurately time the phenological stages of vegetation – which satellites can miss by days or weeks in frequently clouded areas such as the Arctic. In this paper, we describe a measurement network that is distributed across varying plant communities in the high Arctic valley of Adventdalen on the Svalbard archipelago with the aim of monitoring vegetation phenology. The network consists of 10 racks equipped with sensors that measure NDVI (normalized difference vegetation index), soil temperature, and moisture as well as time-lapse RGB cameras (i.e. phenocams). Three additional time-lapse cameras are placed on nearby mountains to provide an overview of the valley. We derived the vegetation index GCC (green chromatic channel) from these RGB photos, which has similar applications as NDVI but at a fraction of the cost of NDVI imaging sensors. To create a robust time series for GCC, each set of photos was adjusted for unwanted movement of the camera with a stabilizing algorithm that enhances the spatial precision of these measurements. This code is available at https://doi.org/10.5281/zenodo.4554937 (Parmentier, 2021) and can be applied to time series obtained with other time-lapse cameras. This paper presents an overview of the data collection and processing and an overview of the dataset that is available at https://doi.org/10.21343/kbpq-xb91 (Nilsen et al., 2021). In addition, we provide some examples of how these data can be used to monitor different vegetation communities in the landscape.

• Virkkala, Anna-Maria; Aalto, Juha; Rogers, Brendan M.; Tagesson, Torbern; Treat, Claire C. & Natali, Susan M. [Show all 49 contributors for this article] (2021). Statistical upscaling of ecosystem CO2 fluxes across the terrestrial tundra and boreal domain: regional patterns and uncertainties. Global Change Biology. ISSN 1354-1013. 27(17), p. 4040–4059. doi: 10.1111/gcb.15659. Full text in Research Archive Show summary

  The regional variability in tundra and boreal carbon dioxide (CO2) fluxes can be high, complicating efforts to quantify sink-source patterns across the entire region. Statistical models are increasingly used to predict (i.e., upscale) CO2 fluxes across large spatial domains, but the reliability of different modeling techniques, each with different specifications and assumptions, has not been assessed in detail. Here, we compile eddy covariance and chamber measurements of annual and growing season CO2 fluxes of gross primary productivity (GPP), ecosystem respiration (ER), and net ecosystem exchange (NEE) during 1990–2015 from 148 terrestrial high-latitude (i.e., tundra and boreal) sites to analyze the spatial patterns and drivers of CO2 fluxes and test the accuracy and uncertainty of different statistical models. CO2 fluxes were upscaled at relatively high spatial resolution (1 km2) across the high-latitude region using five commonly used statistical models and their ensemble, that is, the median of all five models, using climatic, vegetation, and soil predictors. We found the performance of machine learning and ensemble predictions to outperform traditional regression methods. We also found the predictive performance of NEE-focused models to be low, relative to models predicting GPP and ER. Our data compilation and ensemble predictions showed that CO2 sink strength was larger in the boreal biome (observed and predicted average annual NEE −46 and −29 g C m−2 yr−1, respectively) compared to tundra (average annual NEE +10 and −2 g C m−2 yr−1). This pattern was associated with large spatial variability, reflecting local heterogeneity in soil organic carbon stocks, climate, and vegetation productivity. The terrestrial ecosystem CO2 budget, estimated using the annual NEE ensemble prediction, suggests the high-latitude region was on average an annual CO2 sink during 1990–2015, although uncertainty remains high.

• Bruhwiler, Lori; Parmentier, Frans-Jan W.; Crill, Patrick; Leonard, Mark & Palmer, Paul I. (2021). The Arctic Carbon Cycle and Its Response to Changing Climate. Current Climate Change Reports. ISSN 2198-6061. 7, p. 14–34. doi: 10.1007/s40641-020-00169-5. Full text in Research Archive Show summary

  The Arctic has experienced the most rapid change in climate of anywhere on Earth, and these changes are certain to drive changes in the carbon budget of the Arctic as vegetation changes, soils warm, fires become more frequent, and wetlands evolve as permafrost thaws. In this study, we review the extensive evidence for Arctic climate change and effects on the carbon cycle. In addition, we re-evaluate some of the observational evidence for changing Arctic carbon budgets. Observations suggest a more active CO2 cycle in high northern latitude ecosystems. Evidence points to increased uptake by boreal forests and Arctic ecosystems, as well as increasing respiration, especially in autumn. However, there is currently no strong evidence of increased CH4 emissions. Long-term observations using both bottom-up (e.g., flux) and top-down (atmospheric abundance) approaches are essential for understanding changing carbon cycle budgets. Consideration of atmospheric transport is critical for interpretation of top-down observations of atmospheric carbon.

• Pongracz, Alexandra; Wårlind, David; Miller, Paul A. & Parmentier, Frans-Jan W. (2021). Model simulations of arctic biogeochemistry and permafrost extent are highly sensitive to the implemented snow scheme in LPJ-GUESS. Biogeosciences. ISSN 1726-4170. 18(20), p. 5767–5787. doi: 10.5194/bg-18-5767-2021. Full text in Research Archive Show summary

  The Arctic is warming rapidly, especially in winter, which is causing large-scale reductions in snow cover. Snow is one of the main controls on soil thermodynamics, and changes in its thickness and extent affect both permafrost thaw and soil biogeochemistry. Since soil respiration during the cold season potentially offsets carbon uptake during the growing season, it is essential to achieve a realistic simulation of the effect of snow cover on soil conditions to more accurately project the direction of arctic carbon–climate feedbacks under continued winter warming. The Lund–Potsdam–Jena General Ecosystem Simulator (LPJ-GUESS) dynamic vegetation model has used – up until now – a single layer snow scheme, which underestimated the insulation effect of snow, leading to a cold bias in soil temperature. To address this shortcoming, we developed and integrated a dynamic, multi-layer snow scheme in LPJ-GUESS. The new snow scheme performs well in simulating the insulation of snow at hundreds of locations across Russia compared to observations. We show that improving this single physical factor enhanced simulations of permafrost extent compared to an advanced permafrost product, where the overestimation of permafrost cover decreased from 10 % to 5 % using the new snow scheme. Besides soil thermodynamics, the new snow scheme resulted in a doubled winter respiration and an overall higher vegetation carbon content. This study highlights the importance of a correct representation of snow in ecosystem models to project biogeochemical processes that govern climate feedbacks. The new dynamic snow scheme is an essential improvement in the simulation of cold season processes, which reduces the uncertainty of model projections. These developments contribute to a more realistic simulation of arctic carbon–climate feedbacks.

• Olefeldt, David; Hovemyr, Mikael; Kuhn, McKenzie A.; Bastviken, David; Bohn, Theodore J. & Connolly, John [Show all 34 contributors for this article] (2021). The Boreal–Arctic Wetland and Lake Dataset (BAWLD). Earth System Science Data. ISSN 1866-3508. 13(11), p. 5127–5149. doi: 10.5194/essd-13-5127-2021. Full text in Research Archive Show summary

  Methane emissions from boreal and arctic wetlands, lakes, and rivers are expected to increase in response to warming and associated permafrost thaw. However, the lack of appropriate land cover datasets for scaling field-measured methane emissions to circumpolar scales has contributed to a large uncertainty for our understanding of present-day and future methane emissions. Here we present the Boreal–Arctic Wetland and Lake Dataset (BAWLD), a land cover dataset based on an expert assessment, extrapolated using random forest modelling from available spatial datasets of climate, topography, soils, permafrost conditions, vegetation, wetlands, and surface water extents and dynamics. In BAWLD, we estimate the fractional coverage of five wetland, seven lake, and three river classes within 0.5 × 0.5∘ grid cells that cover the northern boreal and tundra biomes (17 % of the global land surface). Land cover classes were defined using criteria that ensured distinct methane emissions among classes, as indicated by a co-developed comprehensive dataset of methane flux observations. In BAWLD, wetlands occupied 3.2 × 106 km2 (14 % of domain) with a 95 % confidence interval between 2.8 and 3.8 × 106 km2. Bog, fen, and permafrost bog were the most abundant wetland classes, covering ∼ 28 % each of the total wetland area, while the highest-methane-emitting marsh and tundra wetland classes occupied 5 % and 12 %, respectively. Lakes, defined to include all lentic open-water ecosystems regardless of size, covered 1.4 × 106 km2 (6 % of domain). Low-methane-emitting large lakes (>10 km2) and glacial lakes jointly represented 78 % of the total lake area, while high-emitting peatland and yedoma lakes covered 18 % and 4 %, respectively. Small (<0.1 km2) glacial, peatland, and yedoma lakes combined covered 17 % of the total lake area but contributed disproportionally to the overall spatial uncertainty in lake area with a 95 % confidence interval between 0.15 and 0.38 × 106 km2. Rivers and streams were estimated to cover 0.12  × 106 km2 (0.5 % of domain), of which 8 % was associated with high-methane-emitting headwaters that drain organic-rich landscapes. Distinct combinations of spatially co-occurring wetland and lake classes were identified across the BAWLD domain, allowing for the mapping of “wetscapes” that have characteristic methane emission magnitudes and sensitivities to climate change at regional scales. With BAWLD, we provide a dataset which avoids double-accounting of wetland, lake, and river extents and which includes confidence intervals for each land cover class. As such, BAWLD will be suitable for many hydrological and biogeochemical modelling and upscaling efforts for the northern boreal and arctic region, in particular those aimed at improving assessments of current and future methane emissions. Data are freely available at https://doi.org/10.18739/A2C824F9X (Olefeldt et al., 2021).

• Chadburn, Sarah E.; Aalto, Tuula; Aurela, Mika; Baldocchi, Dennis; Biasi, Christina & Boike, Julia [Show all 25 contributors for this article] (2020). Modeled Microbial Dynamics Explain the Apparent Temperature Sensitivity of Wetland Methane Emissions. Global Biogeochemical Cycles. ISSN 0886-6236. 34( 11). doi: 10.1029/2020GB006678. Full text in Research Archive Show summary

  Methane emissions from natural wetlands tend to increase with temperature and therefore may lead to a positive feedback under future climate change. However, their temperature response includes confounding factors and appears to differ on different time scales. Observed methane emissions depend strongly on temperature on a seasonal basis, but if the annual mean emissions are compared between sites, there is only a small temperature effect. We hypothesize that microbial dynamics are a major driver of the seasonal cycle and that they can explain this apparent discrepancy. We introduce a relatively simple model of methanogenic growth and dormancy into a wetland methane scheme that is used in an Earth system model. We show that this addition is sufficient to reproduce the observed seasonal dynamics of methane emissions in fully saturated wetland sites, at the same time as reproducing the annual mean emissions. We find that a more complex scheme used in recent Earth system models does not add predictive power. The sites used span a range of climatic conditions, with the majority in high latitudes. The difference in apparent temperature sensitivity seasonally versus spatially cannot be recreated by the non-microbial schemes tested. We therefore conclude that microbial dynamics are a strong candidate to be driving the seasonal cycle of wetland methane emissions. We quantify longer-term temperature sensitivity using this scheme and show that it gives approximately a 12% increase in emissions per degree of warming globally. This is in addition to any hydrological changes, which could also impact future methane emissions.

• Myers-Smith, Isla H.; Kerby, Jeffrey T.; Phoenix, Gareth K.; Bjerke, Jarle W.; Epstein, Howard E. & Assmann, Jakob J. [Show all 41 contributors for this article] (2020). Complexity revealed in the greening of the Arctic. Nature Climate Change. ISSN 1758-678X. 10(2), p. 106–117. doi: 10.1038/s41558-019-0688-1. Full text in Research Archive Show summary

  As the Arctic warms, vegetation is responding, and satellite measures indicate widespread greening at high latitudes. This ‘greening of the Arctic’ is among the world’s most important large-scale ecological responses to global climate change. However, a consensus is emerging that the underlying causes and future dynamics of so-called Arctic greening and browning trends are more complex, variable and inherently scale-dependent than previously thought. Here we summarize the complexities of observing and interpreting high-latitude greening to identify priorities for future research. Incorporating satellite and proximal remote sensing with in-situ data, while accounting for uncertainties and scale issues, will advance the study of past, present and future Arctic vegetation change.

• Pastorello, Gilberto; Trotta, Carlo; Canfora, Eleonora; Chu, Housen; Christianson, Danielle & Cheah, You-Wei [Show all 287 contributors for this article] (2020). The FLUXNET2015 dataset and the ONEFlux processing pipeline for eddy covariance data. Scientific Data. ISSN 2052-4463. 7. doi: 10.1038/s41597-020-0534-3. Full text in Research Archive Show summary

  The FLUXNET2015 dataset provides ecosystem-scale data on CO2, water, and energy exchange between the biosphere and the atmosphere, and other meteorological and biological measurements, from 212 sites around the globe (over 1500 site-years, up to and including year 2014). These sites, independently managed and operated, voluntarily contributed their data to create global datasets. Data were quality controlled and processed using uniform methods, to improve consistency and intercomparability across sites. The dataset is already being used in a number of applications, including ecophysiology studies, remote sensing studies, and development of ecosystem and Earth system models. FLUXNET2015 includes derived-data products, such as gap-filled time series, ecosystem respiration and photosynthetic uptake estimates, estimation of uncertainties, and metadata about the measurements, presented for the first time in this paper. In addition, 206 of these sites are for the first time distributed under a Creative Commons (CC-BY 4.0) license. This paper details this enhanced dataset and the processing methods, now made available as open-source codes, making the dataset more accessible, transparent, and reproducible.

• Box, Jason E.; Colgan, William T.; Christensen, Torben Røjle; Schmidt, Niels Martin; Lund, Magnus & Parmentier, Frans-Jan W. [Show all 20 contributors for this article] (2019). Key indicators of Arctic climate change: 1971–2017 . Environmental Research Letters. ISSN 1748-9326. 14(4). doi: 10.1088/1748-9326/aafc1b. Full text in Research Archive Show summary

  Key observational indicators of climate change in the Arctic, most spanning a 47 year period (1971–2017) demonstrate fundamental changes among nine key elements of the Arctic system. We find that, coherent with increasing air temperature, there is an intensification of the hydrological cycle, evident from increases in humidity, precipitation, river discharge, glacier equilibrium line altitude and land ice wastage. Downward trends continue in sea ice thickness (and extent) and spring snow cover extent and duration, while near-surface permafrost continues to warm. Several of the climate indicators exhibit a significant statistical correlation with air temperature or precipitation, reinforcing the notion that increasing air temperatures and precipitation are drivers of major changes in various components of the Arctic system. To progress beyond a presentation of the Arctic physical climate changes, we find a correspondence between air temperature and biophysical indicators such as tundra biomass and identify numerous biophysical disruptions with cascading effects throughout the trophic levels. These include: increased delivery of organic matter and nutrients to Arctic near‐coastal zones; condensed flowering and pollination plant species periods; timing mismatch between plant flowering and pollinators; increased plant vulnerability to insect disturbance; increased shrub biomass; increased ignition of wildfires; increased growing season CO2 uptake, with counterbalancing increases in shoulder season and winter CO2 emissions; increased carbon cycling, regulated by local hydrology and permafrost thaw; conversion between terrestrial and aquatic ecosystems; and shifting animal distribution and demographics. The Arctic biophysical system is now clearly trending away from its 20th Century state and into an unprecedented state, with implications not only within but beyond the Arctic. The indicator time series of this study are freely downloadable at AMAP.no.

• Natali, Susan M.; Watts, Jennifer D.; Rogers, Brendan M.; Potter, Stefano; Ludwig, Sarah M. & Selbmann, Anne-Katrin [Show all 75 contributors for this article] (2019). Large loss of CO2 in winter observed across the northern permafrost region. Nature Climate Change. ISSN 1758-678X. 9, p. 852–857. doi: 10.1038/s41558-019-0592-8. Full text in Research Archive
• Christensen, Torben R.; Arora, Vivek K; Gauss, Michael; Hoglund-Isaksson, Lena & Parmentier, Frans-Jan W. (2019). Tracing the climate signal: mitigation of anthropogenic methane emissions can outweigh a large Arctic natural emission increase. Scientific Reports. ISSN 2045-2322. 9. doi: 10.1038/s41598-018-37719-9. Full text in Research Archive

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• Lambert, Marius; Tang, Hui; Aas, Kjetil Schanke; Stordal, Frode; Bjerke, Jarle Werner & Fisher, Rosie [Show all 10 contributors for this article] (2023). Winter survival of vegetation in the Arctic-boreal region: Integrating cold hardiness and frost mortality schemes into CLM-FATES.
• Pongracz, Alexandra; Wårlind, David; Miller, Paul A. ; Rabin, Sam S.; Gustafson, Adrian & Parmentier, Frans-Jan (2023). Contrasting trends in snow thickness govern future trajectories of Arctic-boreal carbon release.
• Parmentier, Frans-Jan W. (2022). Vinterskader: Hvordan påvirkes naturen av ekstremt vintervær og vintertørke?
• Parmentier, Frans-Jan; Hessen, Dag Olav & Wang, You-Ren (2022). Ekstremoppvarmingen av Arktis gir økte CO2-utslipp. Dagens næringsliv. ISSN 0803-9372. p. 31–31.
• Lambert, Marius S. A.; Tang, Hui; Aas, Kjetil Schanke; Stordal, Frode; Fisher, Rosie & Bjerke, Jarle W. [Show all 7 contributors for this article] (2022). Towards realistic plant hydraulics and frost damage in the Arctic-Boreal Zone by modelling cold acclimation in CTSM5-Fates (hydro).
• Pongracz, Alexandra; Wårlind, David; Miller, Paul A. & Parmentier, Frans-Jan W. (2022). Quantifying the impact of winter warming on arctic-boreal ecosystems and greenhouse gas exchange.
• Parmentier, Frans-Jan W.; Nilsen, Lennart; Tømmervik, Hans & Cooper, Elisabeth J. (2022). A distributed time-lapse camera network on high-arctic Svalbard to track vegetation phenology with high temporal detail and at varying scales .
• White, Joel D.; Ahrén, Dag; Ström, Lena; Klemedtsson, Leif & Parmentier, Frans-Jan W. (2022). Methane producing and reducing microorganisms display a high resilience to the effects of short term drought in a Swedish hemi boreal fen.
• Parmentier, Frans-Jan W. (2022). Klimaendring er ikke som ­å skru opp varmen med en grad. Klassekampen. ISSN 0805-3839. p. 2–3.
• Parmentier, Frans-Jan W. (2022). På vippepunktet. Klassekampen. ISSN 0805-3839. p. 3–3.
• Aas, Kjetil Schanke; Lambert, Marius; Tang, Hui; Althuizen, Inge; Berntsen, Terje Koren & Fisher, Rosie [Show all 11 contributors for this article] (2022). Recent high-latitude vegetation developments in CLM-FATES.
• Parmentier, Frans-Jan W. (2022). Adjø, Sibir. Klassekampen. ISSN 0805-3839. p. 3–3.
• Parmentier, Frans-Jan W. (2022). Langt, langt borte. Klassekampen. ISSN 0805-3839. p. 3–3.
• Pongracz, Alexandra; Wårlind, David; Miller, Paul A. & Parmentier, Frans-Jan W. (2021). Quantifying the impact of wintertime changes on the arctic carbon cycle.
• Helbig, Manuel; Zivkovic, Tatjana; Alekseychik, Pavel; Aurela, Mika; Euskirchen, Eugénie S. & Flanagan, Lawrence B. [Show all 27 contributors for this article] (2021). Early but not late growing season warming enhances peatland net ecosystem carbon dioxide uptake.
• Lambert, Marius; Aas, Kjetil Schanke; Tang, Hui; Stordal, Frode & Parmentier, Frans-Jan (2021). Modelling insights into the effects of hardening during extreme winter root water release.
• Lambert, Marius (2021). Grønt eller brunt? Uforutsigbar fremtid i Arktis. Naturen. ISSN 0028-0887. 145(5), p. 226–229. doi: 10.18261/issn.1504-3118-2021-05-03.
• Parmentier, Frans-Jan W. (2021). Ingen unnskyldninger. Klassekampen. ISSN 0805-3839. p. 3–3.
• Parmentier, Frans-Jan W. (2021). Zombier i skogen. Klassekampen. ISSN 0805-3839. p. 3–3.
• Parmentier, Frans-Jan W. (2021). Helt på jordet. Klassekampen. ISSN 0805-3839. p. 3–3.
• Parmentier, Frans-Jan W. (2021). Ko-ko-klima! Klassekampen. ISSN 0805-3839. p. 3–3.
• Parmentier, Frans-Jan W. (2021). Permafrost: den sovende klimakjempen. Naturen. ISSN 0028-0887. 145(5), p. 230–235.
• Parmentier, Frans-Jan W. (2021). Komplekst kaos. Klassekampen. ISSN 0805-3839. p. 3–3.
• Parmentier, Frans-Jan W.; Nilsen, Lennart; Tømmervik, Hans & Cooper, Elisabeth J. (2021). A distributed time-lapse camera network on high-arctic Svalbard to track vegetation phenology with high temporal detail and at varying scales. Show summary

  Near-surface remote sensing techniques are essential monitoring tools to provide spatial and temporal resolutions beyond the capabilities of orbital methods. This high level of detail is especially helpful to monitor specific plant communities and to accurately time the phenological stages of vegetation – which satellites can miss by days or weeks in frequently clouded areas such as the Arctic. Therefore, we established a measurement network that is distributed across varying plant communities in the high arctic valley of Adventdalen on the Svalbard archipelago, with the aim to monitor vegetation phenology. The network consists of ten racks equipped with sensors that measure NDVI (Normalized Difference Vegetation Index), soil temperature and moisture, as well as time-lapse RGB cameras. Three additional time-lapse cameras are placed on nearby mountain tops to provide an overview of the valley. From these RGB photos we derived the vegetation index GCC (Green Chromatic Channel), which has similar applications as NDVI but at a fraction of the cost of NDVI imaging sensors. To create a robust timeseries for GCC, each set of photos was adjusted for unwanted movement of the camera with a stabilizing algorithm that enhances the spatial precision of these measurements. We show how this data can be used to monitor different vegetation communities in the landscape and that this can form the basis for a direct comparison to space-borne observations and further upscaling.

• Parmentier, Frans-Jan W. (2021). Hvit jul for Rudolf. Klassekampen. ISSN 0805-3839. p. 3–3.
• Nilsen, Lennart; Parmentier, Frans-Jan W.; Tømmervik, Hans & Cooper, Elisabeth J. (2021). Near-surface vegetation monitoring in Adventdalen, Svalbard (Rack #1-#10, 2015-2018). Show summary

  NDVI, GCC, soil and surface temperature, and soil water content data from Adventdalen, Svalbard. This data was collected with a time-lapse RGB camera and NDVI sensor installed on a two meter high metal rack to monitor tundra vegetation. The time-lapse photos have gone through a manual quality check and were automatically adjusted with an algorithm to correct for lateral and rotational movements. A mask was used to calculate Green Chromatic Channel (GCC) from the photos. The NDVI data was quality controlled by removing outliers that were two standard deviations removed from the mean value of the growing season, and by removing dates where there was snow on the ground (as indicated by the time-lapse photos). In addition, soil and surface temperature and soil moisture were measured to facilitate the interpretation of shifts in the vegetation indices.

• Pongracz, Alexandra; Miller, Paul A.; Wårlind, David & Parmentier, Frans-Jan W. (2020). Model Simulations of Arctic Biogeochemistry and Permafrost Extent Are Sensitive to the Implemented Snow Scheme. Show summary

  The amplified warming of the Arctic is strongest in winter, which is causing large-scale reductions in snow cover. Since snow is one of the main factors governing soil thermodynamics, changes in its thickness and extent also affects permafrost thaw and soil biogeochemistry. Soil respiration during the cold season may have the potential to offset carbon uptake during the growing season. Therefore, a correct simulation of snow cover is essential to project the direction of arctic carbon-climate feedbacks into the future. The Lund-Potsdam-Jena General Ecosystem Simulator (LPJ-GUESS) dynamic vegetation model has used – up until now – a single layer snow scheme, which underestimated the insulation effect of snow leading to a cold bias in soil temperature. To address this shortcoming, we developed and integrated a dynamic, multi-layer snow scheme in LPJ-GUESS and show how improvement of this single physical parameter affects simulations of permafrost extent, vegetation distribution and greenhouse gas exchange. The new snow scheme performs well in simulating the insulation of snow across hundreds of locations across Russia and has a strongly improved correspondence in soil temperatures to a detailed permafrost model. Our analysis shows that the new snow scheme not only influences soil thermodynamics, but also affects soil carbon content, vegetation distribution and biogeochemistry. This study highlights the importance of a correct representation of snow in ecosystem models to realistically project biogeochemical processes that govern climate feedbacks. The implemented dynamic snow scheme prompts further model development in simulating cold season processes, which may reduce the uncertainty of future projections. Ultimately, these developments can contribute to a better understanding of the role of the Arctic in the global carbon cycle.

• Lambert, Marius Stephane Astrid; Tang, Hui; Stordal, Frode; Aas, Kjetil Schanke & Parmentier, Frans-Jan W. (2020). Causes of plant mortality from extreme winter events: model insights into desiccation processes during frost droughts. Show summary

  Arctic and boreal vegetation has experienced significant change during the last decades. Shrubs have grown larger, and trees expand northwards and move upwards along mountain slopes. Although the overall living biomass has gone up, there are significant areas across the Arctic that experienced a decrease in vegetation productivity in recent years – a phenomenon, called "Arctic browning". Part of the reason for arctic browning is a vulnerability to a growing number of extreme weather events associated with climate change. Extreme winter events can initiate icing, loss of frost tolerance, and frost droughts that lead to vegetation damage and death of tissues. While frost droughts are not as well-documented as summer droughts, they are the cause of a considerable proportion of observed damage. They have been suggested to occur when sudden warm events trigger leaf transpiration combined with deeply frozen soils due to the lack of snow that prevent plants from replenishing leaf water loss from soil. Most terrestrial biosphere models represent plant water transport as one single resistance term, or ignore plant hydraulics completely. As a result, leaf transpiration is too strongly regulated by soil water stress, and the disparity between leaf transpiration and soil water stress as expected in frost droughts can hardly be depicted by the models. Recent incorporation of much more detailed plant hydraulic modules, based on tissue (root,stem,leaf) level traits, however, opens up the possibility to properly represent frost droughts experienced by plants, and to investigate how frost droughts impact land-atmosphere interactions. In this study, we used the FATESHydro, a cohort model of vegetation coexistence and competition, driven by high resolution atmospheric forcing derived from COSMO-REA6, to evaluate how frost droughts impact vegetation mortality in northern Norway over the period 2012-2020. We established a clear link between snow depth and drought intensity. We show that root water exudation at low soil water potentials, rather than leaf transpiration loss at high vapor pressure deficit, explained tissue desiccation during shallow snow covered winters. We describe which areas of our domain (northern Norway) are most vulnerable and have been strongly hit by frost droughts over the period 2012-2020.

• Parmentier, Frans-Jan W. (2020). Tampen brenner. Klassekampen. ISSN 0805-3839. p. 3–3.
• Parmentier, Frans-Jan W. (2020). Godt nytt for klimaet? Klassekampen. ISSN 0805-3839. p. 3–3.
• Parmentier, Frans-Jan W. (2020). Arctic Ecosystems: The Thin Green Line Between the Soil and the Atmosphere.
• Parmentier, Frans-Jan W. (2019). Apokalypse nå? Klassekampen. ISSN 0805-3839. p. 3–3.
• Parmentier, Frans-Jan W. (2019). 'Doomsday vault' town warming faster than any other on Earth. [Internet]. CNN Digital.
• Parmentier, Frans-Jan W. (2019). Du grønne glitrende. Klassekampen. ISSN 0805-3839. p. 3–3.
• Parmentier, Frans-Jan W. (2019). Arctic greening and browning: the two-sided impact of global warming on polar ecosystems and climate feedbacks.
• Watts, Jennifer D.; Natali, Sue; Minions, Christina; Ludwig, Sarah; Rogers, Brendan M. & Risk, David [Show all 39 contributors for this article] (2019). Soil CO2 flux in the permafrost zone: New insight from a year-round chamber network in Alaska and Canada.
• Mauritz, Marguerite; Celis, Gerardo; Commane, Roisin; Euskirchen, Eugénie S.; Goeckede, Mathias & Humphreys, Elyn [Show all 19 contributors for this article] (2019). Reconciling Historical and Contemporary Trends in Terrestrial Carbon Exchange of the High-latitude Permafrost-zone.
• Parmentier, Frans-Jan W. (2019). Hva sier planten? Klassekampen. ISSN 0805-3839. p. 3–3.
• Parmentier, Frans-Jan W.; Nilsen, Lennart; Tømmervik, Hans; Meisel, Ove H.; Bröder, Lisa M. & Vonk, Jorien E. [Show all 8 contributors for this article] (2019). Thicker Snow Cover Triggers Permafrost Carbon Loss Through Both Enhanced Warming and Surface Runoff.
• Parmentier, Frans-Jan W. (2019). Ulven under tundraen. [Newspaper]. Klassekampen. Show summary

  Sibir tiner og våkner til live. Ingen vet sikkert hva tøværet bringer:

• Parmentier, Frans-Jan W. (2019). Modellplaneten. Klassekampen. ISSN 0805-3839. p. 3–3.
• Parmentier, Frans-Jan W.; Sonnentag, Oliver; Mauritz, Marguerite; Virkkala, Anna-Maria & Schuur, Edward A.G. (2019). Is the northern permafrost zone a source or a sink for carbon? EOS. ISSN 0096-3941. 100. doi: 10.1029/2019EO130507.
• Parmentier, Frans-Jan W. (2019). Töväder mitt i vintern – ett nytt mönster i vädret kan påverka klimatförändringarna. [Newspaper]. Sydsvenskan. Show summary

  Klimatförändringarna påverkar jorden i allt snabbare takt. Nu måste vi bestämma oss för hur vi ska förhålla oss till det. Det är det viktigaste budskapet i klimatpanelens senaste rapport, säger Frans-Jan Parmentier, klimatforskare vid Lunds universitet.

• Parmentier, Frans-Jan W. (2019). Slår fast att havsstigningen accelererar. [Internet]. Forskning & Framsteg. Show summary

  Havsytan steg i snitt med 15 centimeter under 1900-talet. Nu går stigningen mer än dubbelt så fort, och den accelererar, enligt klimatpanelen IPCC:s rapport om hav och isar.

• Parmentier, Frans-Jan W. (2018). Det varme nord. Klassekampen. ISSN 0805-3839. p. 3–3.
• Natali, Sue; Watts, Jennifer; Rogers, Brendan M.; Potter, Stefano; Abbott, Benjamin & Arndt, Kyle [Show all 72 contributors for this article] (2018). A pan-arctic synthesis of nongrowing season respiration: Key drivers and responses to a changing climate .
• Parmentier, Frans-Jan W. (2018). Pando dør. Klassekampen. ISSN 0805-3839. p. 3–3.
• Christensen, Torben R.; Arora, Vivek K.; Gauss, Michael; Hoglund-Isaksson, Lena & Parmentier, Frans-Jan W. (2018). Arctic methane as an amplifier of global warming.
• Chadburn, Sarah; Fan, Yuanchao; Aalto, Tuula; Aurela, Mika; Bartsch, Annett & Boike, Julia [Show all 25 contributors for this article] (2018). Including microbial dynamics is essential for modelling Arctic methane emissions.
• Parmentier, Frans-Jan W.; Nilsen, Lennart; Tømmervik, Hans; Meisel, Ove; Bröder, Lisa & Vonk, Jorien E. [Show all 8 contributors for this article] (2018). Thicker Snow Cover Triggers Lateral Permafrost Carbon Loss Both Through Enhanced Warming and Surface Runoff.

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