The Nile Basin, a freshwater resource for over 300 million people, faces unprecedented hydrological risks under climate change and transboundary water disputes. Yet, basin-wide projections of extreme streamflow events remain limited by fragmented modeling and insufficient integration of climate uncertainty. Here, we assess future flood risk in downstream countries using a calibrated, climate-driven Soil and Water Assessment Tool model, forced by bias-corrected CMIP6 models under the SSP2-4.5 and SSP5-8.5 scenarios, marking the first application of its kind targeting the Nile Basin downstream regions. Our results indicate a 63% (SSP2-4.5) and 85% (SSP5-8.5) increase in 100-year peak discharges in the 21st century, with extreme floods occurring nearly every decade under high-emission scenarios. Our climate-driven hydrologic modeling, risk analysis, and climate projections emphasize the need for coordinated planning, provide actionable risk information, and a framework for regional cooperation and preparedness to mitigate future flood risks and address water security challenges in the Nile Basin.

Mars' sedimentary rocks record Gyrs of environmental change. New data enable global analyses of paleo-environment relevant physical properties of these rocks, including layer thickness and accumulation rate. Here, using plane-fitting techniques on orbital imagery and elevation models, we find that sedimentary layer thicknesses of post-3.5 Ga rocks across the Martian surface show coherent variations at  ~1000 km-scale that are inconsistent with simple volcanic and climatic hypotheses for formation, which are consistent with global compositional homogeneity at orbital scales. These data combined with analyses of outcrop age and total rock volume revealed a global decrease in layer thickness that predates the eventual drop off in preserved sedimentary rock volume per Myr. These constraints confirm a diachronous transition in Mars' global sedimentary rock record while also highlighting a regional dichotomy in young sedimentary rock deposits that has not been quantified before.

Large-scale tree planting at Canada's northern boreal forest edge offers potential for climate change mitigation, but this capacity is uncertain due to a lack of spatially explicit models. This study quantifies the carbon removal capacity of tree planting at the northwestern boreal edge using a carbon budget model and Monte Carlo estimates. Combining satellite inventory data with probabilistic fire regimes, we simulated total ecosystem carbon under scenarios considering fire return intervals, land classes, planting mortality, and climate variables. Our results indicate that planting ~6.4-32 million hectares could sequester ~3.88-19.4 Gigatonnes of carbon dioxide equivalent over 75 years, with the Taiga Shield West ecozone showing the most potential. Even the conservative estimate is over five times Canada's annual greenhouse gas emissions, a substantial contribution to its 2050 net-zero goal. Further research is needed to refine these estimates, assess economic viability, and investigate impacts on permafrost and albedo.

Accurate basal melt prediction is crucial for assessing ice sheet stability and sea level rise. Recent observations at eastern Thwaites Glacier reported low melt rates despite warm ocean waters. Weak vertical mixing due to low current speeds and strong density stratification suppresses melting. However, the basal melt parameterization approach in ocean models overestimates the melt rates there. Hence, we revisit the parameterization by applying an ice-ocean boundary current model to a simple horizontal ice base. This setting creates a boundary layer (BL) over a dynamically stable pycnocline. We show that the pycnocline's low diffusivity restricts heat transfer, causing models to overpredict melting, especially for weaker far-field currents. While reducing the prescribed BL depth can minimize this overprediction in ocean models, a better fix might be prescribing an upper melt rate limit for slower currents. We also propose a physics-based parameterization framework that more accurately emulates physics in models and observations.

Landforms created by flowing water with sediment have left deposits on the surface of Mars, allowing study of the ancient environment. These features could provide constraints on surface water activity and past habitability. However, only a few lab studies have investigated the appearance and behavior of sediment-rich flows at relevant Mars surface conditions. We conducted experiments in a Mars environment chamber to understand the rheology and deposit morphology of mud under atmospheric pressures from 5 to 1000 mbar and surface temperatures between 248 and 297 K. We found that sediment flows in the Noachian era, when most aqueous activity occurred, could behave similarly to Earth analogs, but only under certain climate conditions. However, in the Hesperian and Amazonian periods, the dominant physical regime changed due to global atmospheric loss. Sediment flows during these eras would not have been similar to Earth analogs, and would have been dominated by freezing, evaporative cooling, and boiling depending on the microclimate (local pressure and temperature). Thus, regional climate and compositional context are important factors for interpreting satellite remote sensing images of these features on Mars. The results suggest we may be able to discover the paleo-atmospheric pressure record on Mars by analyzing sediment flow morphology.

Marine calcifiers support ecosystem services, including shell fisheries and coral reefs. Constraining the saturation state of the calcification media of these organisms is essential to understand the response of biomineralisation to environmental change. Here we synthesise aragonite over variable pH, saturation state, temperature, and in the presence of simple biomolecules. We show that the lithium/magnesium distribution coefficient, relating aragonite and precipitation fluid compositions, is significantly affected by precipitation rate but not by temperature or pH. Precipitation rate reflects saturation state and temperature, so lithium/magnesium of biogenic aragonite can be used to calculate mineral precipitation rate and, if the precipitation temperature is known, to reconstruct calcification medium saturation state. Applying the distribution coefficients to a published calcifier dataset indicates that calcification media saturation state is . 9 to 13 at 18-30 °C and . 6 to 10 at 10-18 °C. Coral calcification media saturation state varies between ocean sites, species, and reef zones.

Reduced and polymerized phosphorus species may have been crucial for the origin and early evolution of life, as they are more reactive and soluble than phosphate. Thermal processes could have produced these phosphorus species; however, the underlying mechanism is poorly constrained, and geological evidence of polymerized species in the Precambrian is so far absent. Here, we investigated contact-metamorphic rocks from the ca. 3.22 Ga Moodies Group (South Africa), where mafic dikes intruded into shallow-marine sediments. We provide evidence of magmatic phosphite (up to 2.85 ppm) and metamorphic polyphosphate (up to 39.3 ppm). Additional laboratory experiments suggest that carbon can facilitate the thermal production of polyphosphates and reduced phosphorus species, including phosphide, from less reactive minerals such as apatite and vivianite. We conclude that magmatic and thermal-metamorphic rocks could have provided soluble and reactive phosphorus species crucial for the origin and early evolution of life.

Achieving the Paris Agreement's goals of holding global temperature rise well below 2 °C with efforts to limit it to 1.5 °C requires rapid reductions in greenhouse gas emissions. The built environment embodies substantial emissions, posing a challenge to meeting these goals. We quantify the carbon cost of constructing the global built-environment over the past three decades and project it to 2050. Our findings indicate that the global construction carbon footprint has doubled over the past three decades and is projected to more than double by 2050. In 2022, over half of the construction industry's carbon emissions stemmed from cementitious materials, bricks, and metals, while glass, plastics, chemicals, and bio-based materials contributed 6%, and the remaining 37% arose from transport, services, machinery, and on-site activities. Under the business-as-usual scenario, the construction carbon footprint alone will exceed the per-annum carbon budget for the 1.5 °C and 2 °C goals in the next two decades. It will use up all remaining carbon budget for the 1.5 °C goal by 2050, as our analysis highlights. Therefore, we advocate for a material revolution, such as replacing traditional materials with biobased materials, which leverages economies of scale and paves the way for a transformative and sustainable future in construction.

Rapid Arctic warming accelerates the erosion of permafrost coasts rich in terrestrial organic carbon (terrOC). Once released into the ocean, terrOC can degrade or get buried in shelf sediments, yet its transport pathways and fate remain poorly understood. We collected permafrost material, sediment and surface water along the Canadian Beaufort Sea coast, fractionating samples by density (cut-off 1.8 g/cm) and size (38, 63 and 200 µm) before performing geochemical and microscopic analysis. Our results show that ~43% of terrOC is trapped in low-density fractions, mainly as vascular plant debris. Surprisingly, this material is trapped within shallow (0-5 m) waters where waterlogging and large particle size increase its density and settling velocity. Less than 10% is transported to deeper waters (30-55 m), indicating that the shallow coastal zone acts as a trap and biogeochemical reactor. These findings challenge the source-to-sink paradigm and highlight the overlooked and undersampled ( < 6% of pan-arctic shelf data) nearshore zone.

Ship emissions are a major source of aerosols over oceans, affecting both air quality and energy balance of the climate. However, estimates of their climate forcing diverge between studies relying on visible ship-tracks and those based on models. Here we show that forcing due to visible ship-tracks accounts for just 5% of the total forcing over the southeast Atlantic shipping-lane. Most forcing from ship emissions comes from aerosols that do not form detectable ship-tracks. They are only tips of the iceberg. We make three forcing calculations, one bottom-up based on visible ship-tracks, one top-down based on spatial relationships, and a hybrid approach that combines top-down or model estimated cloud droplet number concentration changes and cloud adjustments. Although the forcing based on machine learning detected ship tracks is an order of magnitude greater than prior results using manually detected ship-tracks, it remains only 5% of that inferred by top-down or cloud adjustment based methods for pre-2020 shipping. The top-down and the combined cloud adjustments methods show similar forcing for the post-2020 reduction in ships' sulfur emission, although the methods have important regional differences in cloud adjustments that need further investigation. Our results reconcile a long-standing discrepancy in the literature and have important implications for aerosol indirect forcing and marine cloud brightening.

Explosive volcanic eruptions are a major geo-hazard. Given the energetic nature of eruptive processes, direct observation is limited, making the study of deposits and pyroclast textures essential for understanding eruption dynamics. Experimental constraints therefore provide a vital contribution to improving hazard assessment. We performed tumbling experiments using pumice lapilli from the Laacher See eruption (Eifel, Germany) to investigate ash generation and pyroclast shape evolution. Before and after each experimental step, samples were sieved, and the volume and four morphological parameters (axial ratio, convexity, form factor, solidity) of 100 clasts were measured. Most shape change happened before the first 15 min (first experimental step) and produced up to 48 wt.% ash. We frame our analysis in terms of effective relaxation timescales, whereby pyroclasts display a decelerating rate of shape change towards a time-invariant morphology. This quantification of the susceptibility of porous pyroclasts to changes enhances our understanding of transport processes from clast generation to sedimentation.

Reservoirs collectively contribute 1-2% of global anthropogenic greenhouse gas emissions, although individual emissions can vary widely. While emission models have considerably advanced our understanding of the lifetime carbon impacts of reservoirs globally and offer means to inform judicious planning, their widespread adoption is hindered by high manual processing requirements, uncertainties, and linkages to geospatial drivers that can be obscure for planners. Meanwhile, simpler Tier 1 methods fail to capture variability across individual reservoirs and can overestimate national emissions by 50% compared to model-based estimates. Here we introduce an automated and transparent framework for large scale reservoir emission assessments and planning with spatially-explicit emission models to address key limitations in current approaches. By applying our framework to strategic hydropower expansion in Myanmar, we show how emission models can support low-carbon reservoir development at large scales. Our results show that the proposed methodology can yield a hydropower strategy for Myanmar that eliminates 0.94 MtCO in emissions (1% of national total), conserves 239 km of forest and arable land, and reduces the number of barriers in lower river reaches from 28 to 7.

The extinction of woody vegetation in Antarctica remains difficult to constrain due to its fragmented macrofossil record. Despite its long-standing polar position, Antarctica hosted extensive vegetation throughout the Paleogene. This changed near the Eocene-Oligocene Transition (ca. 34 Ma) as glaciation led to vegetation decline. Sparse evidence suggests tundra-like forests persisted until the Pliocene in East Antarctica, but the Neogene record from West Antarctica is largely restricted to palynoflora data. Here, we report early Miocene plant macrofossils from West Antarctica, consisting of leaves. U-Pb zircon geochronology confirms tundra-like vegetation existed in this region during the early Miocene (ca. 22-20 Ma), representing the youngest macrofossil record of West Antarctica. These findings suggest that either persisted through Antarctica's harsh Late Cenozoic Ice Age conditions or recolonised during intermittent warm periods. This substantially advances our understanding of West Antarctica's vegetation history and extends the known record of in Antarctic ecosystems.

The Russian invasion of Ukraine has disrupted crop exports and global food security, overshadowing critical nutrient asymmetry and the associated environmental risks. Here we demonstrate that following nutrient shortages after independence in 1991, fertilizer use increased over 2000-2021, but has decreased sharply following the invasion in early 2022. Input-output balances of nitrogen (N), phosphorus (P) and potassium (K) for staple crops (wheat, maize and sunflower) highlight soil P and K mining since 1991, increasing N surpluses during 2000-2021 and large NPK deficits since the war began in 2022. Based on analysis of five scenarios for 2030, we show how an Integrated Nutrient Management Plan for Ukraine combining manure recycling, precision fertilization and legume expansion is urgently needed, and would maintain crop productivity, significantly reduce nutrient surpluses and improve nutrient use efficiencies up to 80-89%, substantially curtailing environmental pollution and soil degradation.

Accurate methane (CH) emission estimates from Arctic and boreal wetlands are essential for reducing global budget uncertainties but are hindered by poorly constrained wetland distribution and classification. We assessed how land cover map resolution and thematic detail influence these estimates. Using very high spatial resolution land cover maps (≤2.5 m) with five to seven harmonized classes and 4-50% wetland coverage, we estimated CH emissions across seven Arctic and boreal sites in North America and Eurasia. Resampling to coarser resolutions (up to 5 km) revealed that CH flux estimates remained within 13% error when resolution was ≤25 m pixel size. At resolutions coarser than 1 km, four of seven sites shifted from net CH source to sink, due to misrepresentation of wetland extent in heterogeneous landscapes with small, fragmented wetlands. Thematic detail also proved critical, as fens-high CH emitters-were disproportionately underrepresented in coarse (>1 km) maps relative to other wetland types. We also show that existing global or circumpolar land cover maps tend to misrepresent wetlands, either overlooking smaller features or overestimating coverage in wetland dominated areas. Our findings indicate that coarse-scale land cover datasets are unsuitable for estimating CH budgets in these regions, where high spatial resolution and biogeochemically relevant land cover classes are essential for reliable CH emission upscaling.

Passenger aviation carbon footprint calculators often lack breadth, accuracy, transparency, and communication effectiveness, leading to underestimations of environmental impact and mistrust. This study addresses these gaps by developing a comprehensive methodology that broadens scope and improves accuracy. It incorporates nitrogen oxides, water vapour, contrail-induced cloudiness, upstream emissions from in-flight services, and life cycle emissions from aircraft and airports, offering a complete carbon footprint assessment. Accuracy is improved through detailed modelling of flight distance, fuel consumption, and emissions allocation adjusted for passenger class, luggage, and cargo. Historical adjustment factors refine pre-flight estimates by integrating real-world variations. The tool outputs a full emissions breakdown by source, offering unparalleled granularity and clarity. Validated against over 30,000 historical flights, the historical adjustment factor model achieves ~0.5% mean squared percentage error and shows current methods underestimate emissions. This study sets a standard for aviation carbon footprint calculators by enabling transparent, dynamic assessments for industry stakeholders.

The eruption of Hunga volcano on 15 January 2022 was an exceptional event in the satellite era. Record-breaking heights of the volcanic plume were reported, a large amount of water was injected into the stratosphere and a broad spectrum of atmospheric waves were detected. Here, we use satellite measurements to show that a transient ring of small ice particles (~2 m) formed around the plume. We hypothesize that the ice ring was generated by the passage of an atmospheric wave triggered by a pressure pulse at the surface corresponding to a violent explosion that occurred during the 15 January 2022 eruption sequence. The passage of the atmospheric wave produced a transient rarefaction in the upper troposphere-lower stratosphere, which in turn led to oscillations in ambient temperature. Due to the supersaturated state of the atmosphere with respect to ice, ice particles formed in the wake of the radially propagating atmospheric wave, allowing an exceptional opportunity to study ice particle growth via vapour deposition. This atmospheric phenomenon serves as an important natural experiment that reveals the time scale on which ice particles nucleate and grow given an abrupt perturbation in ambient temperature.

Antarctic sea ice exhibits considerable interannual variability and has experienced unprecedented decline over the past decade. Here we provide observational insights into the role of the Southern Annular Mode in driving such variations in Antarctic sea-ice area. The influence of the Southern Annular Mode on Antarctic sea-ice area exhibits more pronounced seasonality than indicated in previous work. Positive anomalies in the Southern Annular Mode lead to decreases in sea-ice area during the seasonal sea-ice maximum, but vice versa during the sea-ice minimum. Variations in Southern Annular Mode during the sea-ice maximum also have an outsized influence on annual-mean changes in sea-ice area, since the seasonally-varying persistence and shortwave effects of sea-ice anomalies peak during the following months. It is argued that a notable fraction of the dramatic losses in annual-mean sea-ice area over the past decade can be traced to variations in the Southern Annular Mode during the sea-ice maximum.

Wildfires are becoming one of the defining climate-related crises of the twenty-first century. We argue that their inclusion in the Loss & Damage framework of the United Nations Framework Convention on Climate Change is essential to support prevention, recovery and justice for the most affected communities.

Wildfires are a key component of Earth system dynamics with respect to carbon cycling. Thus, reconstructing past wildfire dynamics is crucial for understanding potential future climate change as related to (paleo)environmental feedbacks. Here, we explore wildfire during the Early Triassic (Smithian and Spathian, ca. 250 million years ago) - a time interval characterized by scarce fire evidence, perturbation of the carbon cycle, climatic oscillations, vegetation succession and biotic radiation-extinction pulses - using polyaromatic hydrocarbons, which are an organic (geo)chemical fire indicator in sediments. Hydrocarbon abundances in shales from Spitsbergen show a prominent increase after the Smithian-Spathian boundary. Diagnostic ratios of hydrocarbons suggest that these compounds were derived from relatively unaltered biomass as opposed to soil erosion and petrogenic carbon inputs or coal combustion vis-à-vis a coincidental Siberian Trap volcanism. Our data indicates that as temperatures decline during the late Smithian, coeval hydrological conditions become less intense and changing vegetation successions become more amenable to wildfire activity. We hypothesize that changing regional wildfire regimes influenced biogeochemical cycles, potentially affecting long-term carbon sequestration. The observed coupled behavior in water-vegetation-wildfire systems amid key perturbations in Earth's history provides new insights into imminent future climate change consequences.

Aluminum-rich clay minerals are detected across the ancient surface of Mars and record intervals of intense alteration by liquid water. On Earth, these clay minerals can form from hydrothermal alteration or rainfall-driven chemical weathering over thousands to millions of years, but how they formed on Mars remains a mystery. The Perseverance rover discovered light-toned, cobble-sized, aluminum-rich (30-45 wt% AlO) "float" rocks (rock fragments), with some exhibiting spectral signatures of kaolinite, an aluminum-rich clay mineral. These rocks now enable an investigation into the ancient kaolinite-bearing terrains of Mars. To interpret their formation, we use data from the SuperCam and Mastcam-Z instruments onboard the rover to compare the chemistry and reflectance spectra of the float rocks with deeply weathered paleosols and hydrothermal kaolin deposits from Earth's geological record. Aluminum and titanium enrichments coupled with depletion of iron and magnesium are unlike hydrothermal deposits and instead comparable to bleached horizons of paleosols that formed under high rainfall during past greenhouse climates on Earth. These rocks therefore likely represent some of the wettest intervals of Mars' history.