Woodwell Climate Research Center

Warming-induced greenhouse gas emissions from permafrost constitute a major uncertainty in assessments of Earth system stability, remaining carbon budgets, and the feasibility of long-term climate targets. While gradual permafrost thaw is represented in several complex Earth system models, abrupt thaw processes such as thermokarst development and active-layer detachment remain absent, despite their potential to generate rapid and substantial emissions. Here, we quantify the contribution of both gradual and abrupt permafrost thaw to CO2 and CH4 emissions and associated climate risks using the compact Earth system model OSCAR, extended with a newly implemented inventory-based module for abrupt permafrost thaw dynamics. Probabilistic projections of global temperature, sea-level rise, and direct economic damage costs are enabled across seven state-of-the-art scenarios from the Network for Greening the Financial System.Our results show that permafrost carbon feedback introduces pronounced nonlinearities into climate outcomes. Risks associated with gradual thaw scale closely with global warming, whereas abrupt thaw exhibits complex, scenario-dependent effects that disproportionately influence upper-tail risks. These findings suggest that neglecting permafrost thaw may lead to systematic underestimation of tail risks. By explicitly linking permafrost thaw processes to climate risk metrics, this study contributes to reducing a key blind spot in climate‑impact assessments.

Global warming and associated permafrost thaw in the Arctic raise concerns about increased greenhouse gas emissions. Nitrous oxide (N2O) is a potent greenhouse gas produced in soils, but the magnitude of N2O fluxes from permafrost regions remains highly uncertain. While high N2O emissions for nutrient-rich, bare Arctic soils have been reported, for nutrient-poor soils that dominate the region the magnitude and drivers of N2O fluxes have rarely been investigated. We present an unprecedented dataset of 1487 chamber flux observations covering three snow-free seasons in a nutrient-poor thawing permafrost peatland in northern Sweden. Our results show that this ecosystem can act as a continuous and non-negligible, albeit small, sink of N2O during the snow-free season, which has not been reported from in-situ studies before. We also discovered a continuous N2O hotspot that indicates potential for substantial N2O production and net emissions in specific areas of the peatland. Our study identifies complex controls of N2O fluxes, highlighting interactions between photosynthetically active radiation (PAR), carbon dioxide (CO2) fluxes, and other environmental factors. We show that PAR is an important but not exclusive driver, with differences in the set of drivers and shape of dependencies between light and dark conditions.Our results underscore the non-negligible N2O fluxes in nutrient-poor Arctic soils and the presence of hot spots which may be important for the total landscape scale N2O budget. The crucial role of soil-plant-atmosphere interactions in N2O dynamics and the role of light as a driver of N2O flux may have implications for global greenhouse gas budgets and climate mitigation and should be further investigated in future studies.

Abstract. Permafrost soils are one of the largest terrestrial pools of mercury (Hg) in the world, storing an estimated 500–1500 Gg of Hg in the top three meters of soil. Ongoing climate-driven thaw threatens to release this legacy Hg into the environment. Efforts to quantify and model this pool have been hindered by a lack of harmonized, spatially resolved observations. To address this, we compiled a database of 117,802 Hg observations collected between 1988 and 2022 from 59 studies across Arctic, sub-Arctic, and alpine permafrost regions of the Northern Hemisphere, including North America, northern Europe, Eurasian and the Tibetan Plateau. The database includes Hg concentration measurements in solid materials—such as soil, leaves, roots, wood, and litter—as well as in water samples from soil porewater, lakes, and rivers across the northern hemisphere permafrost domain. The database enables cross-site synthesis, model calibration and evaluation, and environmental assessments by standardizing and harmonizing data from diverse sources. Data harmonization steps included unit conversion, categorization of observations by type, and quality control measures to ensure consistency across studies. Analytical uncertainty was preserved where reported in source studies, and qualitative uncertainty indicators and flags were applied where uncertainty information was incomplete or heterogeneous. Mercury concentrations vary widely across observations, with lake sediment showing the highest median values (70 ng g⁻¹, IQR: 45–116), followed by soil (50 ng g⁻¹, IQR: 32–90), and vegetation (15 ng g⁻¹, IQR: 9–33). Water observations had a median of 2 ng L⁻¹ (IQR: 2–6). Statistically significant differences in Hg concentrations among observation types were observed at both global and regional scales, consistently following the pattern: lake sediment > soil > vegetation. These patterns, along with spatial and observation-type biases, highlight the need for improved coverage in underrepresented regions such as Eurasia. The database is freely accessible through Zenodo under the concept DOI 10.5281/zenodo.18300989 (all versions), to support ongoing research and model development in Arctic and sub-Arctic Hg cycle studies.

ABSTRACT To characterize sediment compressibility and permeability in the presence of gas hydrate, a naturally occurring combination of water and methane that requires elevated pressure and reduced temperature to remain stable, a high-stress permeameter (HSP) device was developed. The HSP was designed to accept gas hydrate-bearing pressure core specimens in their plastic liner at pressures of 10–11 MPa. The HSP was further designed to carry out compressibility and permeability tests over a range of effective stresses while maintaining the requirements for gas hydrate stability. To verify the validity of HSP measurements of sediment consolidation properties, we tested remolded kaolin samples in the HSP and three standard fixed-ring oedometers. Furthermore, we compared the direct fluid-flow permeability measurements from the HSP with estimates based on Terzaghi’s log-time method for calculating permeability from 1-dimensional oedometer-style consolidation tests. We found agreement between all devices for consolidation (e.g., coefficients of compressibility and recompression) and permeability results. These findings indicate the suitability of the HSP for consolidation tests, as well as the log-time method for estimating permeability from oedometer consolidation tests.

Abstract. Sediment yields from fluvial networks to the global oceans impact land carbon and nutrient cycles and are susceptible to climate, population, and vegetation changes. The Congo River Basin is a frontier for population and land use change, but sediment yield dynamics are poorly constrained within its basin, in particular within its largest tributary, the Kasaï River. To address this, we aimed to (1) introduce a spatially flexible methodology for estimating sediment yield from remote sensing monitoring, (2) establish a budget for the Congo and Kasaï river basins from both major and secondary tributaries, and (3) better constrain depositional losses of sediment during transit in the mainstem. A random forest model was calibrated on Landsat-8 spectral data, and total suspended sediment was accurately predicted (measured vs. predicted R2 = 0.79), though predictions degraded in highly turbid waters due to spectral saturation. A sediment budget of the Congo River revealed that 33.0 Tg yr−1 are exported to the coastal ocean. Most sediment is derived from Congo River headwaters, the Kasaï River, the Oubangui River, and the Aruwimi River, whereas lower-order tributaries contributed 10 % of all sediment inputs. Meanwhile, major contributors to the Kasaï budget (export = 11.1 Tg yr−1) were the Kasaï headwaters, Sankuru, and Kwango-Kwilu rivers. Finally, we found the Cuvette Centrale, a peatland-dominated depression, to be a depositional hotspot, and we estimated its net sediment deposition to be between 5.96 Tg yr−1 and 9.4 Tg yr−1. By monitoring Congo River Basin sediment transport, we aim to provide a better understanding of the Earth-surface processes occurring in a globally significant and rapidly changing watershed that lacks crucial baseline information on its sediment and carbon cycles.

Research on affective visualization design has shown that color is an especially powerful feature for influencing the emotional connotation of visualizations. Associations between colors and emotions are largely driven by lightness (e.g., lighter colors are associated with positive emotions, whereas darker colors are associated with negative emotions). Designing visualizations to have all light or all dark colors to convey particular emotions may work well for visualizations in which colors represent categories and spatial channels encode data values. However, this approach poses a problem for visualizations that use color to represent spatial patterns in data (e.g., colormap data visualizations) because lightness contrast is needed to reveal fine details in spatial structure. In this study, we found it is possible to design colormaps that have strong lightness contrast to support spatial vision while communicating clear affective connotation. We also found that affective connotation depended not only on the color scales used to construct the colormaps, but also the frequency with which colors appeared in the map, as determined by the underlying dataset (data-dependence hypothesis). These results emphasize the importance of data-aware design, which accounts for not only the design features that encode data (e.g., colors, shapes, textures), but also how those design features are instantiated in a visualization, given the properties of the data.

Abstract The forecast of water exchange between the continental shelf and the coastline is required in a variety of coastal and ocean applications such as sediment budget and coastal morphodynamics evolution. This exchange is controlled by physical processes including hydrodynamics, human interventions, and resulting bathymetric evolution. To improve the understanding of this exchange, field observations, process-based modeling of ocean circulation and sediment processes over the entire shelf and nearshore need to be conducted under varying forcing conditions. Accordingly, circulation over the shore-oblique sand deposits at the shelf offshore of Fire Island, New York, USA has been investigated.

Abstract. Fire is a global phenomenon and a key Earth system process. Extreme fire events have increased in recent years, and fire frequency and intensity are projected to rise across most regions and biomes, posing substantial challenges for ecosystems, the carbon cycle, and society. The Fire Model Intercomparison Project (FireMIP), launched in 2014, has contributed to advancing global fire modeling in Dynamic Global Vegetation Models (DGVMs) and improving understanding of fire's local drivers and local impacts on vegetation and land carbon budgets through land offline (i.e., uncoupled from the atmosphere) simulations. We now bring FireMIP into Coupled Model Intercomparison Project Phase 7 (CMIP7) to: (1) evaluate fire simulations in state-of-the-art fully coupled Earth system models (ESMs); (2) assess fire regime changes in the past, present, and future, and identify their primary natural and anthropogenic forcings and causal pathways within the Earth system, including the associated uncertainties; and (3) quantify the impacts of fires and fire changes on climate, ecosystems, and society across Earth system components, regions, and timescales, and elucidate the underlying mechanisms. FireMIP in CMIP7 will advance the fire and fire-related modeling in fully coupled ESMs, and provide a quantitative, detailed, and process-based understanding of fire's role in the Earth system by using models that incorporate critical climate feedbacks and multi-model, multi-initial-condition, and CMIP7 multi-scenario ensembles. This paper presents the motivation, scientific questions, experimental design and its rationale, model inputs and outputs, and the analysis framework for FireMIP in CMIP7, providing guidance for Earth system modeling teams conducting simulations and informing communities studying fire, climate change, and climate solutions.

Abstract Global warming and permafrost thaw in the Arctic raise concerns about increased greenhouse gas emissions. Nitrous oxide(N 2 O) is a potent greenhouse gas produced in soils, but its fluxes from nutrient-poor Arctic peatlands remain poorly quantified. Here, we present 1,487 chamber flux observations across three snow-free seasons in a nutrient-poor thawing permafrost peatland. Our results reveal this ecosystem acts as a continuous, albeit small N 2 O sink during the snow-free season—unreported in prior in-situ studies. We also identify a persistent N 2 O hot spot, indicating substantial localised production potential. Complex interactions between photosynthetically active radiation (PAR), CO 2 fluxes, and other environmental factors drive N 2 O fluxes, with PAR being important but not exclusive. Differences in drivers and response shapes were evident between light and dark conditions. These findings highlight non-negligible N 2 O fluxes in nutrient-poor Arctic soils and the significance of hot spots for landscape-scale budgets. The critical role of soil-plant-atmosphere interactions and light as a driver has implications for global greenhouse gas budgets and climate mitigation, underscoring the need for further research.

Abstract. Wetland and upland ecosystems play significant but opposing roles in the global methane (CH4) budget, acting as natural sources and sinks, respectively. Two of the most common approaches for measuring CH4 fluxes (FCH4) are chambers, which capture temporally intermittent, fine-scale spatial heterogeneity (ca. 1 m2), and eddy covariance (EC) towers, which cover a larger area (ca. 100–10000 m2) at a longer term. Although chamber and EC observations have been combined in various syntheses and databases to estimate CH4 budgets, a unified cross-site evaluation of FCH4 estimates at plot and ecosystem scales is lacking. As a first step toward a systematic spatiotemporal scaling of EC tower and chamber footprints, we quantified the differences between site-level aggregate FCH4 (EC vs chamber; ΔFCH4) from ten wetland and upland sites at half-hourly, hourly, daily, weekly, monthly, and annual timescales. We found that ecosystem-scale median FCH4 was consistently higher than plot-scale FCH4 at all temporal scales, with the smallest difference at daily timescale (multi-site median ΔFCH4: 1.36 nmol m-2 s-1; ~ 104 % higher ecosystem-scale than plot-scale FCH4) and largest at annual scales (2.58 nmol m-2 s-1; ~ 87 % higher ecosystem-scale than plot-scale FCH4). In general, the agreement between ecosystem- and plot-scale FCH4 decreased with finer temporal resolution (from Spearman ⍴ = 0.95 at annual scale to ⍴ = 0.65 at half-hourly scale), while ΔFCH4 variation was greatest at daily-to-annual scales. Key environmental predictors of ΔFCH4 included plot-scale spatial heterogeneity, dominant vegetation type, vapor pressure deficit, atmospheric pressure, and friction velocity at the daily and monthly scales. Wind direction was a significant predictor only at the monthly scale, suggesting EC footprint effects. These findings suggest accounting for variation in EC footprint extent, chamber measurement placement and artifacts is key to reconciling multi-scale FCH4 observations in diverse ecosystems and refining CH4 budgets.