Understanding long-term interactions between climate, permafrost, and vegetation provides an essential context for interpreting current Arctic greening. Using 65 fossil pollen records from northern Siberia and a Random Forest model trained on a dataset of 835 modern pollen-climate assemblages, we quantitatively reconstructed mean temperature of the warmest month (Mtwa: mean July temperature) anomalies over the past 40 thousand years (ka) and assessed associated vegetation changes. During the Last Glacial Period, herbaceous taxa overwhelmingly dominated, and warming of similar to 1 degrees C during similar to 40-35 cal ka BP was insufficient to deepen the active layer beyond the threshold required for tree establishment, leaving woody cover minimal. In the early Holocene, sustained warming of nearly 2 degrees C triggered permafrost degradation and active-layer thickening, enabling forest expansion, although tree taxa lagged shrubs by several millennia. These results reveal a clear threshold effect in vegetation-permafrost interactions and show that only sustained warming can overcome permafrost constraints. By providing quantitative temperature estimates, our reconstruction offers critical benchmarks for predicting how ongoing Arctic warming may transform vegetation patterns and permafrost stability.

Accurate soil thermal conductivity (STC) data and their spatiotemporal variability are critical for the accurate simulation of future changes in Arctic permafrost. However, in-situ measured STC data remain scarce in the Arctic permafrost region, and the STC parameterization schemes commonly used in current land surface process models (LSMs) fail to meet the actual needs of accurate simulation of hydrothermal processes in permafrost, leading to considerable errors in the simulation results of Arctic permafrost. This study used the XGBoost method to simulate the spatial-temporal variability of the STC in the upper 5 cm active layer of Arctic permafrost during thawing and freezing periods from 1980 to 2020. The findings indicated STC variations between the thawing and freezing periods across different years, with values ranging from-0.4 to 0.28 W & sdot;m-1 & sdot;K-1. The mean STC during the freezing period was higher than that during the thawing period. Tundra, forest, and barren land exhibited the greatest sensitivity of STC to freeze-thaw transitions. This is the first study to explore the long-term spatiotemporal variations of STC in Arctic permafrost, and these findings and datasets can provide useful support for future research on Arctic permafrost evolution simulations.

Carbonaceous aerosols (CA) strongly impact regional and global climate through their light-absorbing and scattering properties, yet their effects remain uncertain in dust-influenced regions. We investigated the optical properties, source contributions, and radiative impacts of CA at two climatically distinct regions in northwestern India: an arid region (AR, Jodhpur; post-monsoon) and a semi-arid region (SAR, Kota; winter). Mean absorption & Aring;ngstr & ouml;m exponent (AAE) values were comparable between the two regions (AR: 1.416 +/- 0.173; SAR: 1.395 +/- 0.069), but temporal cluster analysis revealed source-specific variability, with lower AAE during traffic-dominated periods (similar to 1.30) and elevated AAE during solid fuel and biomass combustion (1.68 in AR and 1.52 in SAR). While equivalent BC (eBC) levels were higher in AR with a relatively uniform liquid-fuel contribution (BClf = 80.06 +/- 1.98 %), the mass absorption cross- of BC (MAC(BC)) in SAR was similar to 4.5X greater, driven by local solid fuel combustion and transported biomass burning emissions (BCsf = 34.61 +/- 6.88 %). Mie modelling indicated higher SSA in AR due to higher contribution of mineral dust, in contrast to SAR, where carbonaceous aerosols caused stronger absorption, forward scattering, and higher imaginary refractive index (k(OBD)). Although absorption enhancement (E-lambda) was slightly higher in AR (similar to 1.11 vs. similar to 0.99), SAR aerosols nearly doubled the warming potential (Delta RFE), with RFE values of similar to 0.87 W/m(2) in SAR versus similar to 0.43 W/m(2) in AR. These findings highlight strong source-specific and site-specific variability in aerosol absorption and radiative, emphasizing the need to integrate region-specific parameters into climate models and air quality assessments for data-scarce arid and semi-arid South Asian environments.

The Himalayan glacier valleys are encountering escalating environmental challenges. One of the contributing factors is thought to be the rising amounts of light-absorbing carbonaceous aerosols, particularly brown carbon (BrC) and black carbon (BC), that are reaching glacier valleys. The present study examines the optical and radiative characteristics of BC at Bhojbasa, near Gaumukh (similar to 3800amsl). Real-time in-situ BC data, optical characteristics, radiative forcing, heating rate, several meteorological parameters, and BC transport pathways to this high-altitude site are investigated. The daily mean concentration of equivalent black carbon (eBC) was 0.28 +/- 0.21 mu g/m(3) over the research period, and the eBC from fossil fuel (BCFF) is dominant with 78 % with a daily mean of 0.22 +/- 0.19 mu g/m(3)(,) and eBC from biomass burning (BCBB) is 22 % with a daily mean of 0.06 +/- 0.08 mu g/m(3). Meteorological data, Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) imaging, and backward air-mass trajectory analysis demonstrate the presence of BC particles and their plausible transit pathways from multiple source locations to the pristine Gangotri Glacier Valley. The estimated daily mean BC radiative forcing values are +6.71 +/- 1.80 W/m(2) in the atmosphere, +1.87 +/- 1.16 W/m(2) at the top of the atmosphere, and -4.84 +/- 1.01 W/m(2) at the surface with a corresponding atmospheric heating rate of 0.19 +/- 0.05 K/day. These findings highlight the critical role of ground-based measurements in monitoring the fluctuations of BC over such varied Himalayan terrain, as they offer important information on the localized trends and effects. Long-term measurements of glacier valleys are essential for a comprehensive evaluation of the impact of BC particles on Himalayan ecology and climate.

Amid global climate change, freeze-thaw cycles in cold regions have intensified, reducing the stability of infrastructures and significantly increasing the demand for grouting reinforcement. However, the deterioration in the durability of existing grouting materials under the combined effects of freeze-thaw cycles and low temperatures has become a major technical bottleneck restricting their application in cold regions. This paper focuses on polyurethane (PU) grouting materials with foaming and lifting characteristics, systematically reviewing the research progress and technical challenges associated with their engineering applications in cold regions. First, in terms of material composition and preparation, the core components and modified additives are detailed to establish a theoretical foundation for performance regulation. Second, addressing the application requirements in cold regions, standardized testing methods and comprehensive evaluation systems are summarized based on key indicators such as heat release temperature, impermeability, diffusion properties, mechanical strength, and expansion properties. Combined with microstructural characteristics, the deformation behavior and failure mechanisms of PU grouting materials under freeze-thaw cycles and salt-freezing environments are revealed. At the engineering application level, the challenges faced by PU grouting materials in cold regions-such as inhibited low-temperature reactivity and insufficient long-term durability-are highlighted. Finally, considering current research gaps, including the unclear mechanisms of microscopic dynamic evolution and the lack of studies on the combined effects of complex environments, future research directions are proposed. This paper aims to provide theoretical support for the development and application of PU grouting materials in cold-region geotechnical engineering.

Black carbon (BC) is a major short-lived climate pollutant (SLCP) with significant climate and environmentalhealth impacts. This review synthesizes critical advancements in the identification of emerging anthropogenic BC sources, updates to global warming potential (GWP) and global temperature potential (GTP) metrics, technical progress in characterization techniques, improvements in global-regional monitoring networks, emission inventory, and impact assessment methods. Notably, gas flaring, shipping, and urban waste burning have slowly emerged as dominant emission sources, especially in Asia, Eastern Europe, and Arctic regions. The updated GWP over 100 years for BC is estimated at 342 CO2-eq, compared to 658 CO2-eq in IPCC AR5. Recent CMIP6-based Earth System Models (ESMs) have improved attribution of BC's microphysics, identifying a 22 % increase in radiative forcing (RF) over hotspots like East Asia and Sub-Saharan Africa. Despite progress, challenges persist in monitoring network inter-comparability, emission inventory uncertainty, and underrepresentation of BC processes in ESMs. Future efforts could benefit from the integration of satellite data, artificial intelligence (AI)assisted methods, and harmonized protocols to improve BC assessment. Targeted mitigation strategies could avert up to four million premature deaths globally by 2030, albeit at a 17 % additional cost. These findings highlight BC's pivotal roles in near-term climate and sustainability policy.

The long-term trend for aerosol optical properties and climate impact sensitivity in terms of radiative forcing efficiency were analyzed at a suburban station in Athens, Southeast Mediterranean, using an extensive dataset from 2008 to 2022. The study examined scattering (nsc) and absorption (nap) coefficients, scattering & Aring;ngstrom exponent (SAE), absorption & Aring;ngstrom exponent (AAE), single scattering albedo (SSA), asymmetry parameter (g), and radiative forcing efficiency (RFE). Seasonal variability was linked to meteorological conditions and human activities. Single Scattering Albedo (SSA) was lowest (0.86), and Radiative Forcing Efficiency (RFE) was highest (-61 W/m2) in winter, confirming enhanced contributions from traffic and biomass burning. Lower SAE values (1.5) in spring indicate a greater presence of coarse particles due to frequent Saharan dust events (SDEs). Daily patterns of nap and SSA reflect local emissions, with pronounced traffic-related peaks. Aerosol classification revealed that Black Carbon (BC) dominates the suburban aerosol (51 %), with mixed BrC-BC (16 %) peaking in winter and dust-pollution mixtures (13 %) increasing in spring. The presence of large particles mixed with BC (11 %) was more frequent in spring, further highlighting seasonal variability. Trend analysis showed statistically significant (ss) decreases in nsc (-0.611) and SSA (-0.003), alongside increases in nap (+0.027) and RFE (+0.270) at a 95 % confidence level, suggesting a shift toward more absorbing aerosols. The findings provide new insights and reveal a new aerosol regime, where a reduction in anthropogenic emissions is affecting the scattering rather than the absorbing aerosol component, while the impact from forest fires as a climate feedback mechanism has a significant effect in the Eastern Mediterranean. It is important for future studies and climate modelling to account for the regionally observed changes of the state of mixing of ambient aerosol leading to a shift in radiative forcing efficiency through the reduction in SSA. This is evident in the long term for the east Mediterranean region and must be accounted for in radiative forcing estimates and future climate projections.

Biomass burning is a major source of carbonaceous aerosols that significantly influences the Earth's radiation balance. However, the spectral light absorption properties of biomass burning aerosols (BBAs), particularly the contribution of brown carbon (BrC), remain poorly constrained due to reliance on laboratory measurements that may not accurately represent real-world atmospheric conditions. To address this limitation, we developed an unmanned aerial vehicle (UAV) based-platform for direct in-situ measurements of BBAs in the ambient atmosphere over the rural North China Plain. This approach reduces biases inherent to laboratory chamber experiments and enables a more realistic characterization of BBAs absorption properties. Our measurements revealed that the absorption & Aring;ngstr & ouml;m exponent (AAE) for typical residential biomass burning was 3.70 +/- 0.04 under smoldering conditions and 1.50 +/- 0.08 under flaming conditions. Variations in AAE were driven primarily by combustion conditions and smoke humidity rather than fuel type. Additionally, field-observed OC/EC ratios were up to ten times higher than those reported in laboratory chamber studies, resulting in systematically lower mass absorption cross-sections. This finding suggests that the BBAs light absorption and radiative forcing estimates in the North China Plain may be systematically overestimated by chamber-based studies. Notably, under smoldering conditions, BrC absorption at 375 nm was up to 6.6 times greater than that of black carbon (BC) once mass emissions are considered, emphasizing that strategies aiming at reducing smoldering combustion could be particularly effective in mitigating the ultraviolet radiative effects of BBAs. Our results demonstrate that ambient atmospheric measurements are essential for accurately constraining BBAs absorption properties and their climate impacts.

Most gravel roads leading to rural areas in Ghana have soft spot sections as a result of weak lateritic subgrade layers. This study presents a laboratory investigation on a typical weak lateritic subgrade soil reinforced with non-woven fibers. The objective was to investigate the strength characteristic of the soil reinforced with non-woven fibers. The California Bearing Ratio and Unconfined Compressive Strength tests were conducted by placing the fibers in single layer and also in multiple layers. The results showed an improved strength of the soil from a CBR value of 7%. The CBR recorded maximum values of 30% and 21% for coconut and palm fibers inclusion at a placement depth of H/5 from the compacted surface. Multiple fiber layer application at depths of H/5 & 2 h/5 yielded CBR values of 38% and 31% for coconut and palm fibers respectively. The Giroud and Noiray design method and the Indian Road Congress design method recorded reduction in the thickness of pavement of 56% to 63% for coconut fiber inclusion and 45% to 55% for palm fiber inclusion. Two-way statistical analysis of variance (ANOVA) showed significant effect of depth of fiber placement and fiber type on the geotechnical characteristics considered. (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic),(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic). (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic). (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic). (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic). (sic)(sic)(sic)(sic),CBR(sic)(sic)7%(sic),(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic). (sic)(sic)(sic)(sic)(sic)(sic)(sic)H/5(sic)(sic)(sic)(sic)(sic)(sic),CBR(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)30%(sic)21%. (sic)H/5(sic)2H/5(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic),(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)CBR(sic)(sic)(sic)(sic)38%(sic)31%. Giroud&Noiray(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)56%(sic)63%,(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)45%(sic)55%. (sic)(sic)(sic)(sic)(sic)(sic)(ANOVA)(sic)(sic),(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic).

On December 18, 2023, a magnitude MS6.2 earthquake struck Jishishan County, Gansu Province, triggering over 40 seismic subsidence sites within a seismic intensity VI zone, 32 km from the epicenter.The earthquake caused tens of millions in economic losses to mountain photovoltaic power stations. Extensive geological surveys and comparisons with similar landslides (such as soil loosening, widespread cracks, and stepped displacements) triggered by the 1920 Haiyuan MS8.5 earthquake and the 1995 Yongdeng MS5.8 earthquake, this study preliminarily identifies one subsidence sites as a seismic-collapsed loess landslide. To investigate its disaster-causing mechanism: the dynamic triaxial test was conducted to assess the seismic subsidence potential of the loess at the site, and the maximum subsidence amount under different seismic loads were calculated by combining actual data from nearby bedrock stations with site amplification data from the active source; simulation of the destabilization evolution of seismic-collapsed loess landslides by large-scale shaking table tests; and a three-dimensional slope model was developed using finite element method to study the complex seismic conditions responsible for site damage. The research findings provide a theoretical foundation for further investigations into the disaster mechanisms of seismic-collapsed loess landslides.