| 1. |
- Bruhwiler, Lori, et al.
(författare)
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The Arctic Carbon Cycle and Its Response to Changing Climate
- 2021
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Ingår i: Current Climate Change Reports. - : Springer Science and Business Media LLC. - 2198-6061. ; 7:1, s. 14-34
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Forskningsöversikt (refereegranskat)abstract
- Purpose of Review: 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. Recent Findings: 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. Summary: 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.
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| 2. |
- Chadburn, Sarah E., et al.
(författare)
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Modeled Microbial Dynamics Explain the Apparent Temperature Sensitivity of Wetland Methane Emissions
- 2020
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Ingår i: Global Biogeochemical Cycles. - 0886-6236 .- 1944-9224. ; 34:11
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
- Euskirchen, Eugénie S., et al.
(författare)
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Current knowledge and uncertainties associated with the Arctic greenhouse gas budget
- 2022
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Ingår i: Balancing Greenhouse Gas Budgets : Accounting for Natural and Anthropogenic Flows of CO2 and other Trace Gases - Accounting for Natural and Anthropogenic Flows of CO2 and other Trace Gases. - 9780128149539 - 9780128149522 ; , s. 159-201
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Bokkapitel (refereegranskat)abstract
- • The Arctic is continuing to warm faster than any other region on Earth, but key uncertainties remain in our knowledge of the Arctic carbon cycle. • We review the most current knowledge pertaining to estimates of arctic greenhouse gas components and discuss uncertainties associated with these measurements and models. • While the Arctic Ocean is consistently estimated as a carbon sink, we have yet to reach an agreement on either the magnitude or the sign of the arctic terrestrial carbon budget. • Much of the uncertainty in the arctic carbon budget is related to the extent of the amount of carbon released as permafrost thaws, the magnitude of shoulder season and winter ecosystem respiration, and the impact of rising temperature and atmospheric [CO2] on plant growth. • We cannot count on the Arctic to store as much carbon as it has in the past, and evidence indicates it will likely store much less.
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| 4. |
- Keetz, Lasse T., et al.
(författare)
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Climate–ecosystem modelling made easy : The Land Sites Platform
- 2023
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Ingår i: Global Change Biology. - 1354-1013. ; 29:15, s. 4440-4452
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Tidskriftsartikel (refereegranskat)abstract
- Dynamic Global Vegetation Models (DGVMs) provide a state-of-the-art process-based approach to study the complex interplay between vegetation and its physical environment. For example, they help to predict how terrestrial plants interact with climate, soils, disturbance and competition for resources. We argue that there is untapped potential for the use of DGVMs in ecological and ecophysiological research. One fundamental barrier to realize this potential is that many researchers with relevant expertize (ecology, plant physiology, soil science, etc.) lack access to the technical resources or awareness of the research potential of DGVMs. Here we present the Land Sites Platform (LSP): new software that facilitates single-site simulations with the Functionally Assembled Terrestrial Ecosystem Simulator, an advanced DGVM coupled with the Community Land Model. The LSP includes a Graphical User Interface and an Application Programming Interface, which improve the user experience and lower the technical thresholds for installing these model architectures and setting up model experiments. The software is distributed via version-controlled containers; researchers and students can run simulations directly on their personal computers or servers, with relatively low hardware requirements, and on different operating systems. Version 1.0 of the LSP supports site-level simulations. We provide input data for 20 established geo-ecological observation sites in Norway and workflows to add generic sites from public global datasets. The LSP makes standard model experiments with default data easily achievable (e.g., for educational or introductory purposes) while retaining flexibility for more advanced scientific uses. We further provide tools to visualize the model input and output, including simple examples to relate predictions to local observations. The LSP improves access to land surface and DGVM modelling as a building block of community cyberinfrastructure that may inspire new avenues for mechanistic ecosystem research across disciplines.
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| 5. |
- Lambert, Marius S.A., et al.
(författare)
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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
- 2022
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Ingår i: Geoscientific Model Development. - : Copernicus GmbH. - 1991-959X .- 1991-9603. ; 15:23, s. 8809-8829
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 6. |
- Lambert, Marius S.A., et al.
(författare)
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Integration of a Frost Mortality Scheme Into the Demographic Vegetation Model FATES
- 2023
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Ingår i: Journal of Advances in Modeling Earth Systems. - 1942-2466. ; 15:7
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Tidskriftsartikel (refereegranskat)abstract
- Frost is damaging to plants when air temperature drops below their tolerance threshold. The set of mechanisms used by cold-tolerant plants to withstand freezing is called “hardening” and typically take place in autumn to protect against winter damage. The recent incorporation of a hardening scheme in the demographic vegetation model FATES opens up the possibility to investigate frost mortality to vegetation. Previously, the hardening scheme was used to improve hydraulic processes in cold-tolerant plants. In this study, we expand upon the existing hardening scheme by implementing hardiness-dependent frost mortality into CLM5.0-FATES to study the impacts of frost on vegetation in temperate and boreal sites from 1950 to 2015. Our results show that the original freezing mortality approach of FATES, where each plant type had a fixed freezing tolerance threshold—an approach common to many other dynamic vegetation models, was restricted to predicting plant type distribution. The main results emerging from the new scheme are a high autumn and spring frost mortality, especially at colder sites, and increasing mid-winter frost mortality due to global warming, especially at warmer sites. We demonstrate that the new frost scheme is a major step forward in dynamically representing vegetation in ESMs by for the first time including a level of frost tolerance that is responding to the environment and includes some level of cost (implicitly) and benefit. By linking hardening and frost mortality in a land surface model, we open new ways to explore the impact of frost events in the context of global warming.
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| 7. |
- Myers-Smith, Isla H., et al.
(författare)
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Complexity revealed in the greening of the Arctic
- 2020
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Ingår i: Nature Climate Change. - : Springer Science and Business Media LLC. - 1758-678X .- 1758-6798. ; 10:2, s. 106-117
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 8. |
- Olefeldt, David, et al.
(författare)
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The Boreal-Arctic Wetland and Lake Dataset (BAWLD)
- 2021
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Ingår i: Earth System Science Data. - : Copernicus Gesellschaft MBH. - 1866-3508 .- 1866-3516. ; 13:11, s. 5127-5149
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Tidskriftsartikel (refereegranskat)abstract
- 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 BorealArctic 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 x 0.5 degrees 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 x 10(6) km(2) (14 % of domain) with a 95 % confidence interval between 2.8 and 3.8 x 10(6) km(2). Bog, fen, and permafrost bog were the most abundant wetland classes, covering similar to 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 x 10(6) km(2) (6 % of domain). Low-methane-emitting large lakes (>10 km(2)) 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 km(2)) 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 x 10(6) km(2). Rivers and streams were estimated to cover 0.12 x 10(6) km(2) (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.
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| 9. |
- Parmentier, Frans-Jan
(författare)
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Permafrost: den sovende klimakjempen
- 2021
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Ingår i: Naturen. - : Scandinavian University Press / Universitetsforlaget AS. - 1504-3118 .- 0028-0887. ; 145:5, s. 230-235
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- SammendragI Arktis er en klimakjempe i ferd med å våkne sakte, men sikkert fra sin lange dvale: Permafrosten – grunn som kan ha vært frosset i tusenvis av år – begynner flere steder å tine på grunn av de sterkt økende temperaturene (Box m.fl. 2019). Dette kan gjøre klimaproblemet enda verre enn det allerede er, fordi det kan føre til store utslipp av drivhusgasser som CO2 og metan (CH4). Når det skjer, varmes klimaet opp enda mer, som gjør at mer permafrost tiner, slik at flere drivhusgasser igjen slipper ut – og så videre. En selvforsterkende effekt med andre ord, og et mulig vippepunkt i klimasystemet. Men hvor stor er sjansen for at dette virkelig vil skje, og hvordan er det i det hele tatt mulig at drivhusgasser slipper ut i det høye nord?
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| 10. |
- Parmentier, Frans Jan W., et al.
(författare)
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A distributed time-lapse camera network to track vegetation phenology with high temporal detail and at varying scales
- 2021
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Ingår i: Earth System Science Data. - : Copernicus GmbH. - 1866-3508 .- 1866-3516. ; 13:7, s. 3593-3606
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Tidskriftsartikel (refereegranskat)abstract
- 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 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 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.
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