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Extreme cold events (ECEs) have intensified in East Asia over the past decades, disrupting socio‐economic activities and public health. Understanding the mechanism and accurate prediction are crucial yet challenging. This study explores the causes and prediction biases for a severe ECE in Beijing‐Tianjin‐Hebei (BTH) during the 2022 Winter Olympics. Two upper‐tropospheric quasi‐biweekly oscillations (QBWO), propagating eastward along the mid‐ and high‐latitudes, respectively, have been confirmed to trigger a low‐tropospheric cyclonic anomaly (LCA) via potential vorticity advection and meridional secondary circulation. This LCA generated the BTH ECE by reducing incoming solar radiation due to increased snowfall and cloud cover, and by advecting cold air into BTH. Both the subseasonal dynamical prediction and long‐term historical observational diagnosis further indicate a strong connection between mid‐high‐latitude QBWO and the regional ECEs. This research deepens our understanding of the ECE mechanisms and underscores the need for improving the prediction of extratropical subseasonal signals for better forecasting of extreme events. Plain Language Summary In February 2022, an extreme cold event affected the Beijing‐Tianjin‐Hebei (BTH) region during the Winter Olympics, posing significant challenges to public health and economic activities. This study investigates the main subseasonal atmospheric conditions that caused this extreme cold spell by observational diagnostics and subseasonal prediction analyses. Two propagating quasi‐biweekly oscillations (QBWO) contributed to the development of the event by generating and enhancing a low‐level cyclonic anomaly, which created favorable conditions for cold air accumulation over BTH. The fidelity of the dynamic model to the mid‐high‐latitude QBWO signals determines the accuracy of the subseasonal prediction of such cold events. Key Points Quasi‐biweekly oscillations (QBWO) play a key role in the 2022 extreme cold event (ECE) in Beijing‐Tianjin‐Hebei (BTH) region Mid‐ and high‐latitude QBWO waves jointly trigger and sustain the BTH ECE Prediction skill of mid‐high‐latitude QBWO signals determines the success or failure of the ECE subseasonal prediction

1. Climate warming is predicted to alter ecological boundaries in high-latitude ecosystems including the elevational or latitudinal extent of tall shrubs in Arctic and alpine tundra. Over 60 studies from 128 locations around the tundra biome have investigated shrub expansion in tundra ecosystems; however, only six studies test whether shrublines are actually advancing up hill-slopes or northward into tundra where tall shrubs are currently absent. 2. We test the hypothesis that willow shrublines have expanded to higher elevations in relation to climate across a 50 × 50 km area in the Kluane Region of the southwest Yukon Territory, Canada by surveying of 379 shrubs at 14 sites and sampling of 297 of the surveyed shrubs at 10 sites. We compared growth and recruitment to climate variables to test the climate sensitivity of shrub increase using annual radial growth analysis, age distributions and repeat field surveys to estimate the current rate of shrubline advance. 3. We found consistent and increasing rates of recruitment of alpine willows, with estimates of faster advancing shrublines on shallower hill-slopes. Mortality was extremely low across the elevation gradient. Aspect, elevation and species identity did not explain variation in recruitment patterns, suggesting a regional factor, such as climate, as the driver of the observed shrubline advance. 4. Annual radial growth of willows was best explained by variation in summer temperatures, and recruitment pulses by winter temperatures. Measured recruitment rates are ~20 ± 5 individuals per hectare per decade (M ± SE) and measured rates of increased shrub cover of ~5 ± 1% per decade (M ± SE) measured at the Pika Camp site between field surveys in 2009 and 2013. Our results suggest that shrubline will continue to advance over the next 50 years, if growing conditions remain suitable. However, if future conditions differ between summer and winter seasons, this could lead to contrasting trajectories for recruitment vs. growth, and influence the vegetation change observed on the landscape. 5. Synthesis. Our findings in the context of a review of the existing literature indicate that elevational and latitudinal shrublines, like treelines, are advancing in response to climate warming; however, the trajectories of change will depend on the climate drivers controlling recruitment vs. growth.

We systematically evaluate the high‐latitude Joule heating of the recently released version 3.0 Thermosphere Ionosphere Electrodynamics General Circulation Model (TIE‐GCM) by comparison to EISCAT incoherent scatter radar measurements. The model performance is examined using normalized root mean square deviations derived from test runs driven by different convection patterns from empirical and data‐assimilated models. The following features are revealed: (a) Data‐assimilated geomagnetic forcing improves the agreement between modeled and EISCAT‐derived Joule heating rates by 8%, 28%, and 54% for low, moderate, and high geomagnetic activity. (b) Increasing model grid resolution from 2.5° to 1.25° leads to ∼${\\sim} $ 20% higher Joule heating rates. (c) AMIE‐driven runs better reproduce the magnitude of the Joule heating rates, AMGeO‐driven runs the vertical profile. (d) Internal model time step resolution has no effect on the Joule heating rates.

The gradient drift instability (GDI) commonly occurs in the high‐latitude ionosphere and is widely recognized for producing elongated striation structures. While previous studies have established the linear growth and primary nonlinear development of striations, the formation of secondary structures remains not fully understood. Using two‐dimensional numerical simulations, we show that smaller branch structures evolve asymmetrically on the sides of striations when either the background electric field or the wave vector has a component along the density gradient. Our results indicate that in the linear stage, the electric field in the direction of density gradient modifies the effective growth rate by altering the wave vector orientation. In the nonlinear stage, electric field and wave vector direction coupling govern the emergence of branch structure, with electric field dominating when its effect opposes that of the wave vector. These results highlight the critical roles of electric field and wave vector orientation in generating secondary GDI structures.

Amplified warming has altered the phenology and structure of high‐latitude forests, yet their carbon uptake responses to environmental variations remain uncertain. Using satellite observations of solar‐induced chlorophyll fluorescence (SIF), we quantify interannual variations in growing‐season (GS) productivity of these forests and their climatic drivers. GS productivity is largely controlled by early‐ and peak‐season temperatures: warmer springs enhance carbon uptake and, despite moderate legacy declines later in the season, overall productivity increases in warmer years in most regions. Pronounced heterogeneity is observed among plant functional types—deciduous needleleaf forests (DNF) show weaker temperature sensitivity and stronger water dependence than other forests. In DNF, temperature effects weaken or reverse under dry conditions and persist after accounting for canopy structural effects, indicating strong water constraints on physiological responses. These results underscore the heterogeneous climate sensitivities of high‐latitude forests and highlight SIF as a powerful tool for monitoring their productivity and responses to climate.

The global atmospheric CO2 growth rate in 2023–2024 reached an unprecedented level, exceeding all records since modern monitoring began. Using a CO2 flux inversion, constrained by column‐averaged CO2 observations from Greenhouse gases Observing SATellite (GOSAT), we investigated spatio‐temporal drivers of this anomaly. The 2023–2024 El Niño seem to have increased non‐fossil CO2 fluxes globally; however, unlike the former big 2015–2016 El Niño, which was dominated by tropical anomalies (0.96 PgC year−1), the 2023–2024 event exhibited not only distinct tropical increases (1.11 Pg C year−1) but also notable weakening of net CO2 uptake (0.42 PgC year−1) across northern mid‐to‐high latitudes, whose flux variations have less sensitivity to El Niño in the past. The flux variability in the northern mid‐to‐high latitudes was primarily temperature‐associated, while fire emissions contributed only weakly and episodically.

Marine microalgae within seawater and sea ice fuel high-latitude ecosystems and drive biogeochemical cycles through the fixation and export of carbon, uptake of nutrients, and production and release of oxygen and organic compounds. High-latitude marine environments are characterized by cold temperatures, dark winters and a strong seasonal cycle. Within this environment a number of diverse and dynamic habitats exist, particularly in association with the formation and melt of sea ice, with distinct microalgal communities that transition with the season. Algal physiology is a crucial component, both responding to the dynamic environment and in turn influencing its immediate physicochemical environment. As high-latitude oceans shift into new climate regimes the analysis of seasonal responses may provide insights into how microalgae will respond to long-term environmental change. This review discusses recent developments in our understanding of how the physiology of highlatitude marine microalgae is regulated over a polar seasonal cycle, with a focus on iceassociated (sympagic) algae. In particular, physiologies that impact larger scale processes will be explored, with an aim to improve our understanding of current and future ecosystems and biogeochemical cycles.

Aim Biodiversity is currently undergoing rapid restructuring across the globe. However, the nature of biodiversity change is not well understood, as community‐level changes may hide differential responses in individual population trajectories. Here, we quantify spatio‐temporal community and stability dynamics using a long‐term high‐quality moth monitoring dataset. Location Finland, Northern Europe. Time period 1993–2012. Major taxa studied Nocturnal moths (Lepidoptera). Methods We quantified patterns of change in species richness, total abundance, dominance and temporal variability at different organizational levels over a 20 year period and along a latitudinal gradient of 1,100 km. We used mixed‐effects and linear models to quantify temporal trends for the different community and stability metrics and to test for latitudinal (or longitudinal) effects. Results We found contrasting patterns for different community metrics, and strong latitudinal patterns. While total moth abundance has declined, species richness has simultaneously increased over the study period, but with rates accelerating with latitude. In addition, we revealed a latitudinal pattern in temporal variability—the northernmost locations exhibited higher variability over time, as quantified by both metrics of richness and aggregated species population trends. Main conclusions When combined, our findings likely reflect an influx of species expanding their ranges poleward in response to warming. The overall decline in abundance and the latitudinal effect on temporal variability highlight potentially severe consequences of global change for community structure and integrity across high‐latitude regions. Importantly, our results underscore that increases in species richness may be paralleled by a loss of individuals, which in turn might affect higher trophic levels. Our findings suggest that the ongoing global species redistribution is affecting both community structure and stability over time, leading to compounded and partly opposing effects of global change depending on which biodiversity dimension we focus on.

Vegetation phenology is a key biological indicator for monitoring terrestrial ecosystems and global change, and regions with the most obvious phenological changes in vegetation are primarily located at high latitudes and altitudes. Over the past three decades, investigations of obvious phenological changes in vegetation at middle and high latitudes in the Northern Hemisphere have provided significant contributions to understanding global climate change. In this study, phenological parameters were extracted from the Global Inventory Modeling and Mapping Studies (GIMMS) Normalized Difference Vegetation Index (NDVI3g) to analyze the spatial and temporal characteristics of vegetation phenological changes above 40°N in the Northern Hemisphere from 1982–2013. The results showed that the start of season (SOS) was significantly advanced (−2.2 ± 0.6 days·decade−1, p < 0.05) and that the end of season (EOS) was slightly delayed (0.78 ± 0.6 days·decade−1, p = 0.21) over the entire study area in the initial 21 years (1982–2002). When the time scale was extended to 2013, the change rate of the SOS and EOS was significantly reduced; in addition, the SOS was delayed (3.2 ± 1.7 days·decade−1, p < 0.05), and the EOS was advanced (4.5 ± 0.9 days·decade−1, p < 0.05) over the entire study area in the last 11 years (2003–2013). The trends of advanced SOS and delayed EOS over the past three decades were slower than those over the initial two decades on a hemispheric scale. The change trends showed obvious variability with different vegetation types and were greater for woody plants than for herbaceous plants. For broad-leaved forest, the SOS was significantly advanced (2 ± 0.5 days·decade−1, p < 0.05) and the EOS was significantly delayed (2.7 ± 0.6 days·decade−1, p < 0.05) from 1982–2013. The trend of delayed EOS was greater than that of advanced SOS for different vegetation types. With respect to the spatial distribution of phenological trends in the Northern Hemisphere, the trends of advanced SOS and delayed EOS were strongest in Europe followed by North America, and the trends were least significant in Asia. Coniferous forest, shrub forest, grassland, and the entire study area have the same change trends for the two time periods (1982–2002 and 2003–2013), and the increased rate of the phenology parameters has decelerated over the most recent decade. The length of season (LOS) of broad-leaved forest and mixed forest over the past 32 years shows a strong increased trend, and simultaneously, the SOS and EOS show an advanced trend and a delayed trend, respectively

Wildfires, increasingly frequent extreme events driven by global change, have significantly accelerated the release of mercury (Hg) stored in soils. However, a systematic quantification of Hg emissions from topsoil heating during global wildfires has been lacking. This study proposes a novel method for estimating these emissions, based on quantitative formulas that link soil heating depths with fire temperature and fire radiative power. Our results estimate that annual soil Hg emissions from topsoil heating during 2008–2019 were 98.1 Mg yr−1 (24.5–290.0 Mg yr−1). Emission hotspots were predominantly located in northern high‐latitude (25%) and tropical regions (41%). In high‐latitude regions, substantial historical Hg accumulation in soils, combined with rising wildfire frequency and intensity, contributed to significant emissions. In tropical regions, frequent wildfires and high atmospheric Hg deposition were the main drivers. This study provides crucial data to enhance global Hg emission inventories and improves the understanding of how wildfires impact global Hg cycling. Plain Language Summary Mercury (Hg) is a toxic metal that harms both human health and global ecosystems. Soils act as a major reservoir for Hg, and with the increasing frequency of wildfires driven by climate change, substantial amounts of Hg are released into the atmosphere through topsoil heating. However, these emissions have not yet been systematically quantified. This study presents a new method for initially estimating these emissions, using formulas that link soil heating depth with fire temperature and fire radiative power. The results highlight that high‐latitude regions, where legacy Hg emissions are significant, are particularly vulnerable to increased wildfire frequency, which could worsen Hg‐related risks in these regions. By including wildfire‐induced soil emissions, this study fills a crucial gap in global Hg emission inventories and improves our understanding of the environmental risks associated with wildfires. Key Points A novel method for initially estimating global soil Hg0 emissions driven by topsoil heating during wildfires Total soil Hg0 emissions were estimated at 98.1 Mg yr−1 with major hotspots in northern high‐latitude and tropical regions Increasing frequency of wildfires are expected to exacerbate Hg‐related risks to the high‐latitude regions in a changing climate