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European Geosciences Union

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Light scattering and microphysical properties of atmospheric bullet rosette ice crystals

Understanding the interaction between cirrus clouds and solar radiation is critical for modeling the Earth’s climate. A common crystal type found in cirrus clouds is the bullet rosette. Here, atmospheric bullet rosettes measured from jet aircraft are analyzed for their morphological and radiative properties. Atmospheric bullet rosettes are found to be more morphologically complex than previously assumed. This complexity has a significant impact on their radiative properties.

Warnings based on risk matrices: a coherent framework with consistent evaluation

Natural Hazards and Earth System Sciences
DOI 10.5194/nhess-25-2657-2025
13 August 2025

Our research presents a new method for determining warning levels for any hazard. Using risk matrices, our framework addresses issues found in other approaches. Illustrative examples demonstrate how the approach works. A powerful method for evaluating warning accuracy is given, allowing for a cycle of continuous improvement in warning services. This research is relevant to a broad audience, from those who develop forecast systems to practitioners who issue or communicate warnings.

Invited perspectives: Thunderstorm intensification from mountains to plains

Natural Hazards and Earth System Sciences
DOI 10.5194/nhess-25-2629-2025
8 August 2025

Strong thunderstorms have been studied mainly over flat terrain in the past. However, they are particularly frequent near European mountain ranges, so observations of such storms are needed. This article gives an overview of our existing knowledge on this topic and presents plans for a large European field campaign with the goals to fill the knowledge gaps, validate tools for thunderstorm warnings, and improve numerical weather prediction near mountains.

Consequences of the Aral Sea restoration for its present physical state: temperature, mixing, and oxygen regime

The Aral Sea is both an example of large-scale environmental degradation caused by human activity and a message of hope through its partial restoration. Our study shows that the restored part of the Aral Sea is now healthy in terms of vertical mixing and oxygenation. However, small perturbations of water level or transparency could significantly alter the entire ecosystem. The results contribute to understanding the consequences of large-scale lake management worldwide.

Subsurface manifestation of marine heat waves in the southwestern Indian Ocean

Marine heat waves (MHWs) are prolonged periods of extreme ocean temperatures with significant impacts on marine ecosystems. Much research has focused on surface MHWs, but less is known about their subsurface extent. This study uses satellite and in situ data to investigate MHWs in the southwestern Indian Ocean (SWIO). We find that MHWs in the SWIO are closely linked to mesoscale eddies and that strong temperature anomalies extend below surface-identified MHWs.

A Bayesian framework for inferring regional and global change from stratigraphic proxy records (StratMC v1.0)

The chemistry of sedimentary rocks is used to reconstruct past changes in Earth’s climate and biogeochemical cycles. Reconstructing global change requires merging stratigraphic proxy records from many locations, each of which may be incomplete, time-uncertain, and influenced by both global and local processes. StratMC uses Bayesian modeling to see through this complexity, building more accurate and testable reconstructions of global change from stratigraphic data.

Opinion: The role of AerChemMIP in advancing climate and air quality research

The Aerosol Chemistry Model Intercomparison Project (AerChemMIP) aimed to quantify the climate and air quality impacts of aerosols and chemically reactive gases. We review its contribution to AR6 (Sixth Assessment Report of the Intergovernmental Panel on Climate Change) and the wider understanding of the role of these species in climate and climate change. We identify challenges and provide recommendations to improve the utility and uptake of climate model data, detailed summary tables of CMIP6 models, experiments, and emergent diagnostics.

Characterization of the 1966 Camp Century subglacial core: a multiscale analysis

The Camp Century subglacial core stores information about past climates and glacial and interglacial processes in northwestern Greenland. In this study, we investigated the core archive, making large-scale observations using computed tomography (CT) scans and micron-scale observations observing physical and chemical characteristics of individual grains. We find evidence of past ice-free conditions, weathering processes during warmer periods, and past glaciations.

Quantifying the soil sink of atmospheric hydrogen: a full year of field measurements from grassland and forest soils in the UK

We measured soil hydrogen (H₂) fluxes from two field sites, a managed grassland and a planted deciduous woodland, with flux measurements of H₂ covering full seasonal cycles. We estimate annual H₂ uptake of −3.1 ± 0.1 and −12.0 ± 0.4 kg H₂ ha⁻¹ yr⁻¹ for the grassland and woodland sites, respectively. Soil moisture was found to be the primary driver of H₂ uptake, with the silt/clay content of the soils providing a physical barrier which limited H₂ uptake.

Leveraging the satellite-based climate data record CLARA-A3 to understand the climatic trend regimes relevant for solar energy applications over Europe

By compositing trends in multiple climate variables, this study presents emerging regimes that are relevant for solar energy applications. It is shown that the favourable conditions for exploiting solar energy are emerging during spring and early summer. The study also underscores the increasingly important role of clouds in regulating surface solar radiation as the aerosol concentrations are decreasing over Europe and the societal value of satellite-based climate monitoring.

asQ: parallel-in-time finite element simulations using ParaDiag for geoscientific models and beyond

Effectively using modern supercomputers requires massively parallel algorithms. Time-parallel algorithms calculate the system state (e.g. the atmosphere) at multiple times simultaneously and have exciting potential but are tricky to implement and still require development. We have developed software to simplify implementing and testing the ParaDiag algorithm on supercomputers. We show that for some atmospheric problems it can enable faster or more accurate solutions than traditional techniques.

Thermal state of permafrost in the Central Andes (27–34° S)

This study presents the first regional compilation of borehole temperature data from high-altitude permafrost sites in the Andes, providing a baseline of ground thermal conditions. Data from 53 boreholes show thermal characteristics similar to other mountain permafrost areas, but uniquely shaped by Andean topo-climatic conditions. The study emphasizes the need for ongoing monitoring and is a notable collaboration between industry, academia, and regulators in advancing climate change research.

Marine snow morphology drives sinking and attenuation in the ocean interior

Key parameters representing the gravity flux in global models are sinking speed and vertical attenuation of exported material. We calculate, for the first time, these parameters in situ in the ocean for six intermittent blooms followed by export events using high-resolution (3 d) time series of 0–1000 m depth profiles from imaging sensors mounted on an Argo float. We show that sinking speed depends not only on size but also on the morphology of the particles, with density being an important property.

Occupancy history influences extinction risk of fossil marine microplankton groups

We examine how change in a species’ geographic range size over time influences that species’ extinction risk. We analyze instantaneous range size and range size change and how these terms relate to extinction risk in marine microplankton. We find that both the instantaneous range size and the change in range size are informative predictors of extinction. Using predictive models, we also assess extinction probability in four extant groups.

The value of hydroclimatic teleconnections for snow-based seasonal streamflow forecasting in central Asia

Seasonal streamflow forecasts for snowmelt-dominated catchments often rely on snowpack data, which are not always available and are prone to errors. Our study evaluates near-real-time global snow estimates and climate oscillation indices for predictions in the data-scarce mountains of central Asia. We show that climate indices can improve prediction accuracy at longer lead times, help offset snow data uncertainty, and enhance predictions where streamflow depends on in-season climate variability.

Calibrated sea level contribution from the Amundsen Sea sector, West Antarctica, under RCP8.5 and Paris 2C scenarios

Glaciers in the Amundsen Sea region of Antarctica have been retreating and losing mass, but their future contribution to global sea level rise remains highly uncertain. We use an ice sheet model and uncertainty quantification methods to evaluate the probable range of mass loss from this region for two future climate scenarios. We find that the rate of ice loss until 2100 will likely remain similar to present-day observations, with little sensitivity to climate scenario over this short time frame.

Delineating the technosphere: definition, categorization, and characteristics

The technosphere – including buildings, infrastructure, and all other non-living human creations – is a major part of our planet, but it is not often considered as an integrated part of Earth system processes. Here we propose a refined definition of the technosphere, intended to help with integration. We also characterize the functional end uses, map the global distribution, and discuss the catalytic properties that underlie the exponential growth of the trillion tonne technosphere.

Distribution of alkylamines in surface waters around the Antarctic Peninsula and Weddell Sea

During the PolarChange expedition, volatile alkylamines, important players in nitrogen cycling and cloud formation, were measured in Antarctic waters using a high-sensitivity method. Trimethylamine was the dominant alkylamine in marine particles, associated with nanophytoplankton. Dissolved dimethylamine likely originated from trimethylamine degradation, while diethylamine sources remain unclear. These findings confirm the biological origin of alkylamines in polar marine microbial food webs.

Observational constraints suggest a smaller effective radiative forcing from aerosol–cloud interactions

This study addresses the long-standing challenge of quantifying the impact of aerosol–cloud interactions. Using satellite observations, reanalysis data, and a “perfect-model” cross-validation, we show that explicitly accounting for aerosol–cloud droplet activation rates is key to accurately estimating ERFaci (effective radiative forcing due to aerosol–cloud interactions). Our results indicate a smaller and less uncertain ERFaci than previously assessed, implying the reduced role of aerosol–cloud interactions in shaping climate sensitivity.

Simulating vertical phytoplankton dynamics in a stratified ocean using a two-layered ecosystem model

Phytoplankton contribute to half of Earth’s primary production, but not a lot is known about subsurface phytoplankton, living at the base of the sunlit ocean. We develop a two-layered box model to simulate phytoplankton seasonal and interannual variations in different depth layers of the ocean. Our model captures seasonal and long-term trends of the two layers, explaining how they respond to a warming ocean, furthering our understanding of how phytoplankton are responding to climate change.