Permafrost Feedback Research Articles

Effect of methane mitigation on global temperature under a permafrost feedback

Earth systems may fall into an undesirable system state if 1.5°C of warming is exceeded. Carbon release from substantial permafrost stocks vulnerable to near-term warming represents a positive climate feedback that may increase the risk of 1.5°C warming or greater. Methane (CH4) is a short-lived but powerful greenhouse gas with a global warming potential 28.5 times that of carbon dioxide (CO2) over a 100 year time span. Because permafrost thaw in the coming centuries is partly determined by the warming in the 21st century, rapid reductions in methane emissions early in the 21st century could have far reaching effects. We use a reduced complexity carbon cycle model and a permafrost feedback module to explore the possibility that accelerating reductions in methane emissions could help avoid long-term warming by limiting permafrost melt. We simulate three extended Representative Concentration Pathway (RCP) emission scenarios (RCP 2.6, 4.5, and 6) through the year 2300 and impose methane mitigation strategies where we reduce CH4 emissions by 1%, 5% or 10% annually until the long-term scenario emission level is reached. We find that accelerated rates of methane mitigation do not sufficiently alter the global temperature anomaly to prevent or delay a permafrost feedback, nor do they result in meaningful long term reductions in temperatures. We find that the long-term magnitude of methane mitigation (i.e., long-term emission level) and not the rate of reduction, corresponds to long-term temperature change. Further study of methane-climate dynamics is necessary to fully resolve this question.

Permafrost degradation at two monitored palsa mires in north-west Finland

Abstract. Palsas and peat plateaus are expected to disappear from many regions, including Finnish Lapland. However, detailed long-term monitoring data of the degradation process on palsas are scarce. Here, we present the results of the aerial photography time series analysis (1959–2021), annual real-time kinematic (RTK) GNSS and active layer monitoring (2007–2021), and annual unoccupied aerial system surveys (2016–2021) at two palsa sites (Peera and Laassaniemi, 68∘ N) located in north-west Finland. We analysed temporal trends of palsa degradation and their relation to climate using linear regression. At both sites, the decrease in palsa area by −77 % to −90 % since 1959 and height by −16 % to −49 % since 2007 indicate substantial permafrost degradation throughout the study periods. The area loss rates are mainly connected to winter air temperature changes at Peera and winter precipitation changes at Laassaniemi. The active layer thickness (ALT) has varied annually between 2007 and 2021 with no significant trend and is related mainly to the number of very warm days during summer, autumn rainfall of previous year, and snow depths at Peera. At Laassaniemi, the ALT is weakly related to climate and has been decreasing in the middle part of the palsa during the past 8 years despite the continuous decrease in palsa volume. Our findings imply that the ALT in the inner parts of palsas do not necessarily reflect the overall permafrost conditions and underline the importance of surface position monitoring alongside the active layer measurements. The results also showed a negative relationship between the ALT and snow cover onset, indicating the complexity of climate–permafrost feedbacks in palsa mires.

A globally relevant stock of soil nitrogen in the Yedoma permafrost domain

Nitrogen regulates multiple aspects of the permafrost climate feedback, including plant growth, organic matter decomposition, and the production of the potent greenhouse gas nitrous oxide. Despite its importance, current estimates of permafrost nitrogen are highly uncertain. Here, we compiled a dataset of >2000 samples to quantify nitrogen stocks in the Yedoma domain, a region with organic-rich permafrost that contains ~25% of all permafrost carbon. We estimate that the Yedoma domain contains 41.2 gigatons of nitrogen down to ~20 metre for the deepest unit, which increases the previous estimate for the entire permafrost zone by ~46%. Approximately 90% of this nitrogen (37 gigatons) is stored in permafrost and therefore currently immobile and frozen. Here, we show that of this amount, ¾ is stored >3 metre depth, but if partially mobilised by thaw, this large nitrogen pool could have continental-scale consequences for soil and aquatic biogeochemistry and global-scale consequences for the permafrost feedback.

Topological climate change with permafrost feedback

Climate models predict that the climate of the Earth is warming and will continue to warm in coming centuries, if there is no mitigation. A recent energy balance model [Kypke et al., Nonlin. Process. Geophys. 27 (2020) 391–409] forecasts that, if the current increase of carbon dioxide in the atmosphere continues unabated, then in the next century the climate of the Earth will not only get warmer, but will transition abruptly via a bifurcation, to a warm equable climate unlike any climate seen on Earth since the Pliocene. This transition to a new climate state is a topological change. That model includes the effects of water vapour feedback and ice albedo feedback, as well as ocean and atmospheric heat transport. This paper adds to that model further amplification by permafrost feedback. That is, as the Arctic warms, permafrost will thaw, releasing large amounts of the greenhouse gases carbon dioxide and methane, which cause further warming. Since knowledge of permafrost stores and release rates is limited, a range of permafrost carbon release sensitivities (Q 10) is considered. The model predicts that permafrost feedback accelerates the timing and increases the likelihood of a topological climate change in the Arctic, and reinforces the view that permafrost feedback should not be ignored in Anthropocene climate models.

Plant trait response of tundra shrubs to permafrost thaw and nutrient addition

Abstract. Plant traits reflect growth strategies and trade-offs in response to environmental conditions. Because of climate warming, plant traits might change, altering ecosystem functions and vegetation–climate interactions. Despite important feedbacks of plant trait changes in tundra ecosystems with regional climate, with a key role for shrubs, information on responses of shrub functional traits is limited. Here, we investigate the effects of experimentally increased permafrost thaw depth and (possibly thaw-associated) soil nutrient availability on plant functional traits and strategies of Arctic shrubs in northeastern Siberia. We hypothesize that shrubs will generally shift their strategy from efficient conservation to faster acquisition of resources through adaptation of leaf and stem traits in a coordinated whole-plant fashion. To test this hypothesis, we ran a 4 year permafrost thaw and nutrient fertilization experiment with a fully factorial block design and six treatment combinations – permafrost thaw (control, unheated cable, heated cable) × fertilization (no nutrient addition, nutrient addition). We measured 10 leaf and stem traits related to growth, defence and the resource economics spectrum in four shrub species (Betula nana, Salix pulchra, Ledum palustre and Vaccinium vitis-idaea), which were sampled in the experimental plots. The plant trait data were statistically analysed using linear mixed-effect models and principal component analysis (PCA). The response to increased permafrost thaw was not significant for most shrub traits. However, all shrubs responded to the fertilization treatment, despite decreased thaw depth and soil temperature in fertilized plots. Shrubs tended to grow taller but did not increase their stem density or bark thickness. We found a similar coordinated trait response for all four species at leaf and plant level; i.e. they shifted from a conservative towards a more acquisitive resource economy strategy upon fertilization. In accordance, results point towards a lower investment into defence mechanisms, and hence increased shrub vulnerability to herbivory and climate extremes. Compared to biomass and height only, detailed data involving individual plant organ traits such as leaf area and nutrient contents or stem water content can contribute to a better mechanistic understanding of feedbacks between shrub growth strategies, permafrost thaw and carbon and energy fluxes. In combination with observational data, these experimental tundra trait data allow for a more realistic representation of tundra shrubs in dynamic vegetation models and robust prediction of ecosystem functions and related climate–vegetation–permafrost feedbacks.

Soil moisture as a key factor in carbon release from thawing permafrost in a boreal forest

The feedback between the atmosphere and permafrost soils containing large carbon stocks is currently considered the most important carbon-cycle feedback, but it is missing from climate models due to many uncertainties. Knowledge of how differences in post-thaw hydrological conditions affect carbon (C) release is critical for predicting permafrost feedback, but this knowledge remains limited. In this study, permafrost and active layer soils from the southern margin of the Eurasian boreal permafrost region in Northeast China were collected and incubated under experimentally modified moisture to monitor their CO2 and CH4 productions under simulated natural, drier and flooded conditions. We also characterized soil properties related to soil organic carbon (SOC) quality and microbial activities to determine their relations with measured C productions. We found that permafrost had higher C release per gram of SOC basis (C vulnerability) than the active layer, which suggested that there would be a high risk for C emissions in the permafrost region when permafrost thaws in the warming future. However, hydrological conditions following the permafrost thaw control these emissions. Permafrost C decomposed in relatively aerobic upland systems had higher C emissions than that decomposed in anaerobic wetland environments. Our results suggest a greater climate forcing of C release in aerobic than anaerobic conditions, but there are some uncertainties resulting from the unknown long-term CH4 production rates. Moreover, we found that the aerobic C production in permafrost after thawing could be constrained by water stress, suggesting that previous predictions based on soil incubations at natural soil moisture might overestimate the aerobic permafrost C release.

Climate policy implications of nonlinear decline of Arctic land permafrost and other cryosphere elements

Arctic feedbacks accelerate climate change through carbon releases from thawing permafrost and higher solar absorption from reductions in the surface albedo, following loss of sea ice and land snow. Here, we include dynamic emulators of complex physical models in the integrated assessment model PAGE-ICE to explore nonlinear transitions in the Arctic feedbacks and their subsequent impacts on the global climate and economy under the Paris Agreement scenarios. The permafrost feedback is increasingly positive in warmer climates, while the albedo feedback weakens as the ice and snow melt. Combined, these two factors lead to significant increases in the mean discounted economic effect of climate change: +4.0% ($24.8 trillion) under the 1.5 °C scenario, +5.5% ($33.8 trillion) under the 2 °C scenario, and +4.8% ($66.9 trillion) under mitigation levels consistent with the current national pledges. Considering the nonlinear Arctic feedbacks makes the 1.5 °C target marginally more economically attractive than the 2 °C target, although both are statistically equivalent.

Author Correction: Carbon budgets for 1.5 and 2 °C targets lowered by natural wetland and permafrost feedbacks

In the version of this Article originally published, a parallelization coding problem, which meant that a subset of model grid cells were subjected to erroneous updating of atmospheric gas concentrations, resulted in incorrect calculation of atmospheric CO2 for these grid cells, and therefore underestimation of the carbon uptake by land through vegetation growth and eventual increases to soil carbon stocks. Having re-run the simulations using the corrected code, the authors found that the original estimates of the impact of the natural wetland methane feedback were overestimated. The permafrost and natural wetland methane feedback requires lower permissible emissions of 9–15% to achieve climate stabilization at 1.5 °C, compared with the original published estimate of 17–23%. The Article text, Table 1 and Fig. 3 have been updated online to reflect the revised numerical estimates. The Supplementary Information file has also been amended, with Supplementary Figs 6, 7, 8 and 9 replaced with revised versions produced using the corrected model output. As the strength of feedbacks remain significant, still require inclusion in climate policy and are nonlinear with global warming, the overall conclusions of the Article remain unchanged.

Carbon budgets for 1.5 and 2 °C targets lowered by natural wetland and permafrost feedbacks

Global methane emissions from natural wetlands and carbon release from permafrost thaw have a positive feedback on climate, yet are not represented in most state-of-the-art climate models. Furthermore, a fraction of the thawed permafrost carbon is released as methane, enhancing the combined feedback strength. We present simulations with an inverted intermediate complexity climate model, which follows prescribed global warming pathways to stabilization at 1.5 or 2.0 °C above pre-industrial levels by the year 2100, and which incorporates a state-of-the-art global land surface model with updated descriptions of wetland and permafrost carbon release. We demonstrate that the climate feedbacks from those two processes are substantial. Specifically, permissible anthropogenic fossil fuel CO2 emission budgets are reduced by 9–15% (25–38 GtC) for stabilization at 1.5 °C, and 6–10% (33–52 GtC) for 2.0 °C stabilization. In our simulations these feedback processes respond more quickly at temperatures below 1.5 °C, and the differences between the 1.5 and 2 °C targets are disproportionately small. This key finding holds for transient emission pathways to 2100 and does not account for longer-term implications of these feedback processes. We conclude that natural feedback processes from wetlands and permafrost must be considered in assessments of transient emission pathways to limit global warming. Climate feedbacks associated with wetland methane emissions and permafrost-thaw carbon release substantially reduce available carbon budgets to achieve temperature targets, suggest simulations with a climate–land-surface model system.

Estimation and Sensitivity of Carbon Storage in Permafrost of North-Eastern Yakutia

Organic carbon derived from permafrost can provide a substrate for greenhouse gas production where the buried carbon pool thaws and mobilizes into biogeochemical cycles. Much attention has focused on the permafrost carbon of the Yedoma region of Siberia due to the wide distribution of organic and ice‐rich deposits. Here, we present a new estimation of carbon storage in the upper 25 m of permafrost in north‐eastern Yakutia based on a novel database of total carbon (TC) content, bulk density and ice content of permafrost, and a new map of Quaternary deposits derived from drilling data. The stratigraphic units contain 0.6–2.1% TC, with the highest concentrations in the Holocene cover layer and Late Pleistocene Yedoma superhorizon. The largest carbon pool is found in the Pliocene/Middle Pleistocene Olyor superhorizon. The TC pool of Yedoma is estimated to be 1.5–2 times less than that calculated previously. The TC pool of the study area is 31.2 ± 15.2 Pg C spread across 88 000 km2, with a mean specific carbon content of approximately 14.3 kg C m−3. Carbon storage is estimated excluding the ice‐wedge volume and, due to the limited data for Yedoma and Alas deposits, we present a maximal assessment of the carbon pool for the Yedoma region. Refinement of the size of the Yedoma TC pool is critical for quantifying the scale of permafrost feedback to the carbon cycle. Copyright © 2017 John Wiley & Sons, Ltd.

Ecohydrological feedbacks between permafrost and vegetation dynamics

The presence of forest vegetation can aid in preserving the permafrost layer by maintaining lower soil temperatures via the accretion of an organic layer at the surface. This layer has a low bulk density and low thermal conductivity (due also to high evapotranspiration rates by forest vegetation), which insulates ice-rich permafrost. Forest removal can lead to significant increases in the summer soil temperature, which increases the thickness of the active layer (i.e., the surficial layer above permafrost which thaws during summer and freezes again in winter) and causes a rise in the active layer towards the surface. When vegetation is sensitive to saturated soil conditions, a rise in the active layer can lead to the conversion of forested areas to wetlands. In this manuscript, we develop a modeling framework to relate vegetation–permafrost feedbacks to the emergence of multiple stable ecosystem states. Factors related to soil temperature and hydrologic characteristics of the system were examined to see how they affect the location of the stable and unstable states. This model was also used to examine how an increase in precipitation would affect the temporal dynamics of the active layer and vegetation. Results show that the presence of forest vegetation can enhance the resilience of the system in that it is less prone to state shifts following a disturbance. Understanding these dynamics is important given, (i) the rapid rate at which these systems can shift between states, (ii) the projected climatic changes for forested areas underlain by permafrost and (iii) the high rates of forest loss in these areas.