Deliberate, large-scale interventions in the Earth’s climate system, collectively known as “geoengineering”, are increasingly being proposed to counteract the worst effects of global warming. Public and scholarly controversies have ensued due to the high risks and high uncertainties that characterise these novel technologies. For all that, geoengineering is currently being evaluated at the highest levels of governance, and a full-scale review by the United Nations is ongoing. To enrich the understanding of geoengineering, the present work reviews the metaphysics behind the main arguments in favour and against geoengineering. Based on the varied conceptions of humans, nature, knowledge, and technical systems, which support their appraisals, proponents and opponents of climate engineering are grouped into four ideal-types: homo naturans, homo faber, homo sapiens, and anthropo-not-seen. In addition to the pro-against geoengineering fissure, a second one is identified: transcendental-instrumental metaphysics.

Carbon-14 in tree rings have suggested that there had been multiple extreme solar proton events (SPEs) in the past. While the largest events such as in 774–775 CE can be significantly detected by the typical precision of accelerator mass spectrometry, smaller but possibly more frequent events have been difficult to be detected. Thus, the frequency or any characteristics of such relatively smaller events are still largely unknown. In this paper, we report that multiple large SPEs had occurred before the onset of the Wolf grand solar minimum based on high-precision carbon-14 analyses. It is suggested that they had occurred at the maximum and the declining phase of solar cycles, and that they had occurred during the transition time of solar activity into a deep minimum. We propose that this episode may provide a unique opportunity to elucidate a potential interaction between the solar dynamo and extreme solar flares.

Forearc basin stratigraphy is expected to record a detailed history of the deformation and growth pattern of an accretionary wedge. However, the relationship between syntectonic basin sedimentation and growth of a wedge remains poorly understood, including (1) how deformation of the wedge modifies the basin stratigraphy and (2) how syntectonic sedimentation influences deformation of the wedge. In this study, we conducted scaled analogue sandbox experiments to reproduce accretionary wedges with and without syntectonic sedimentation. The results show that basin stratigraphy varied with the growth pattern of the accretionary wedge. In the case that wedge growth was dominated by trenchward accretion, the depositional area migrated landward. In contrast, prolonged underthrusting caused the sediment layers to be tilted landward and the depocenter to migrate landward. The occurrence of two types of basin stratigraphy (i.e., trenchward and landward migration of the depocenter) reflects a contrast in strength of the basal shear resistance between the inner and outer parts of the wedge due to sedimentation on the wedge. A change in the magnitude of normal stress acting on the wedge base likely influenced the mode of deformation of the wedge. A phase dominated by underthrusting can result in the combining a retro-wedge basin with a wedge-top basin, and yield a wide area of accommodation space in the forearc basin. These results suggest that forearc basin stratigraphy is influenced by the growth pattern of an accretionary wedge that is affected by syntectonic sedimentation.

A document by Wen-Pin Hsieh. Click on the document to view its contents.

Freshwater pulses (during which river discharge is much higher than average) occur in many estuaries, and strongly impact estuarine functioning. To gain insight into the estuarine salinity response to freshwater pulses, an idealized model is presented. With respect to earlier models on the spatio-temporal behavior of salinity in estuaries, it includes additional processes that provide a more detailed vertical structure of salinity. Simulation of an observed salinity response to a freshwater pulse in the Guadalquivir Estuary (Spain) shows that this is important to adequately simulate the salinity structure. The model is used to determine the dependency of the estuarine salinity response to freshwater pulses for different background discharge, tides and different intensities and durations of the pulses. Results indicate that the change in salt intrusion length due to a freshwater pulse is proportional to the ratio between peak and background river discharge and depends linearly on the duration of the pulse if there is no equilibration during the pulse. The adjustment time, which is the time it takes for the estuary to reach equilibrium after an increase in river discharge, scales with the ratio of the change in salt intrusion length and the peak river discharge. The recovery time, i.e. the time it takes for the estuary to reach equilibrium after a decrease in river discharge, does not depend on the amount of decrease in salt intrusion length caused by the pulse. The strength of the tides is of minor importance to the salt dynamics during and after the pulse.

Land use change driven by human activities plays a critical role in terrestrial carbon budget through habitats loss and vegetation change. Despite projections of global population and economic growth under the framework of the shared socioeconomic pathways (SSPs) have been analyzed, little is known about land use /cover change (LUCC) at a fine spatial resolution and how carbon pools respond to LUCC under different SSP scenarios. Here, we projected the future global LUCC at 1‐km spatial resolution and 10‐year time step from 2010 to 2100, after which its direct impacts on aboveground biomass carbon (AGB) under SSP scenarios were explored. We found that scenario SSP3 yields the highest global cropland expansion, among which about 48% is expected to locate in current forest land and 46% locate in current grassland. Scenario SSP1 has the largest forest expansion, and it is mainly converted from the grassland (54%) and cropland (30%). Due to the spatial change of land use/cover, global AGB loss is expected to reach about 9.16 Pg C in 2100 under scenario SSP3 while increase about 1.75 Pg C under scenario SSP1. Africa is expected to undergo 58% loss of AGB under scenario SSP3. Aboveground biomass in Asia will fix 3.05 Pg C to reverse the AGB loss in 2100 under scenario SSP1. These findings suggest land use development and management is one of key measures to mitigate negative impacts of LUCC on biomass carbon pool.

How lightning initiates inside thunderclouds remains a major puzzle of atmospheric electricity. By monitoring optical emissions from thunderstorms, the Atmosphere-Space Interactions Monitor (ASIM) onboard the International Space Station is providing new clues about lightning initiation by detecting Blue LUminous Events (BLUEs), which are manifestations of an enigmatic type of electrical discharge that sometimes precedes lightning and is named “fast breakdown”. Here we combine optical and radio observations from a thunderstorm near Malaysia to uncover a new type of event containing multiple optical and radio pulses. We find that the first optical pulse coincides with a strong radio signal in the form of a Narrow Bipolar Event (NBE) but subsequent optical pulses, delayed some milliseconds, have weaker radio signals, possibly because they emanate from a horizontally oriented fast breakdown which does not trigger full-fledged lightning. Our results cast light on the differences between isolated and lightning-initiating fast breakdown.

Indian summer monsoon rainfall is strongly influenced by various large-scale atmosphere-ocean oscillations including Pacific Decadal Oscillation (PDO), and El Niño-Southern Oscillation (ENSO). Researchers have shown that the negative phase of PDO or La Niña episodes of ENSO produce higher magnitude rainfall and hence relatively wetter years. So, it is imperative to have better knowledge of flood characteristics in the Indian watersheds for optimal planning and design of various infrastructure, and for optimal planning and management of reservoir operations. Traditionally, such information is estimated using flood frequency analysis (FFA) for small and medium sized projects. However, the adequacy of traditionally accepted assumption that the annual peak flows are independent and identically distributed (i.i.d.) is questioned globally \cite{Gurrapu_2016,Milly_2008}. This study evaluates the influence of PDO and ENSO and flood characteristics in Godavari River, India. The results indicate that the flood magnitude and frequency at majority of the selected gauges in Godavari River Basin is significantly influenced by PDO and ENSO, higher magnitude floods are associated with negative phase of PDO and La Niña episodes of ENSO. A few gauges are inversely related to these teleconnections. The influence of these teleconnections on regional climate is spatially variable across India and so are the contrasting results. The results from this study benefits the design engineers for efficient design of water resources infrastructures and water managers for optimal planning and management of reservoir operations. 

The performance in term of tropical cyclone track and intensity prediction of the new coupled ocean-atmosphere system based on the operational atmospheric model AROME-Indian Ocean and the ocean model NEMO is assessed against that of the current operational configuration in the case of seven recent tropical cyclones. Five different configurations of the forecast system are evaluated: two with the coupled system, two with an ocean mixed layer parameterization and one with a constant sea surface temperature. For each ocean-atmosphere coupling option, one is initialized directly with the MERCATOR-Ocean PSY4 product as in the current operational configuration and the other with the ocean state that is cycled in the AROME-NEMO coupled suite since a few days before the cyclone intensification. The results show that the coupling with NEMO improves the intensity of cyclones in AROME-IO, especially when they encounter a slow propagation phase. For short-term forecasts (less than 36 hours), the presence of a cooling in the initial state that has been triggered by the AROME high-resolution cyclonic winds in a previous coupled forecast already improves the tropical cyclone intensity for all coupled or uncoupled configurations. However, the simplification of the ocean-atmosphere interactions in the configurations using the ocean mixed layer parameterization is not the only reason for the overestimation of the intensity of already well-developed TC in AROME-IO. The impact of other model components, such as the air-sea flux parameterization and the cloud microphysics scheme will need to be further investigated.

Airborne Doppler radar observations of the wind field in the tropical cyclone boundary layer (TCBL) during the landfall of Hurricane Ida (2021) are examined here. Asymmetries in tangential and radial flow are governed by TC motion and vertical wind shear prior to landfall, while frictional effects dominate the asymmetry location during landfall. Strong TCBL inflow on the offshore-flow side of Ida occurs during landfall, while the location of the peak tangential wind at the top of the TCBL during this period is located on the onshore-flow side. A comparison of these observations with a numerical simulation of TC landfall shows many consistencies with the modeling study, though there are some notable differences that may be related to differences in the characteristics of the land surface between the simulation and the observations here.

A document by Joseph K. Ansong. Click on the document to view its contents.

Significant sediment flux and deposition in a sedimentary system are influenced by climate changes, tectonics, lithology, and the sedimentary system’s internal dynamics. Identifying the timing of depositional periods from stratigraphic records is a first step to critically evaluating the controls of sediment flux and deposition. Here, we show that ages of single-grain K-feldspar luminescence subpopulations may provide information on the timing of previous major depositional periods. We analyzed 754 K-feldspar single-grains from 17 samples from the surface to ~9 m-depth in a trench located downstream of the Mission Creek catchment. Single-grain luminescence subpopulation ages significantly overlap at least eight times since ~12.0 ka indicating a common depositional history. These depositional periods correspond reasonably well with the wetter climate periods based on hydroclimatic proxies from nearby locations. Our findings imply a first-order climatic control on sediment depositional history in southern California on a millennial timescale.

The timing and location of microcracking events, their propagation and coalescence to form macrocracks, and their development by tension, shearing or mixed modes are little known but essential to understanding the fracture of intact rock by freezing and thawing. The aims of the present study are to investigate the mechanisms and transition of micro- and macrocracking during repeated freeze–thaw, and to develop a statistical model of crack propagation that assesses the distance and angular relationship of neighbouring cracking events arranged in their temporal order of occurrence. Eight acoustic emission (AE) sensors mounted on a 300 mm cubic block of chalk captured the three-dimensional locations of microcracking events in their temporal order of occurrence during 16 seasonal freeze‒thaw cycles simulating an active layer above permafrost. AE events occurred mostly during thawing periods (45%) and freeze-to-thaw transitions (37%) rather than during freezing periods (9%) and thaw-to-freeze transitions (8%), suggesting that most AE (microcrack) events were driven by the process of ice segregation rather than volumetric expansion. The outcomes of a novel statistical model of crack propagation based on two boundary conditions—inside–out and outside–in modes of cracking—were assessed based on Bayes’ theorem by testing the hypothesis that the inside–out mode of cracking was favoured by tensional activity, whereas the outside–in mode supported by shearing events. In both situations, the hypothesis accounted for 54–73% confidence level. The microcrack propagation model can distinguish reasonably between cracks formed by volumetric expansion and ice segregation.

Global, regional and local sea-level projections rely on complex process-based models of the climate-ocean-cryosphere system. While extrapolation of observational data has been examined on global and regional scales, this approach has not yet been used for the additional complexities of local coastal sea-level projections. Here, we evaluate the sea level trend and acceleration for a global network of tide-gauge observations over 1970-2023, which are then extrapolated to provide local projections up to 2050 and compared with the process-based projections from the IPCC Sixth Assessment Report (AR6). For 2050 relative to 2020, the observation-based projections agree with AR6 process-based projections within the 90% uncertainty range at the majority (99%) of 237 tide gauges. Thus, the observation-based projections provide complementary perspectives of near-term local sea-level changes, and this agreement provides increased confidence in the current understanding and projections of sea-level changes over coming decades.

Localized frictional sliding on faults in the continental crust transitions at depth to distributed deformation in viscous shear zones. This brittle-ductile transition (BDT), and/or the transition from velocity-weakening (VW) to velocity-strengthening (VS) friction, are controlled by the lithospheric thermal structure and composition. Here we investigate these transitions, and their effect on the depth extent of earthquakes, using 2D antiplane shear simulations of a strike-slip fault with rate-and-state friction. The off-fault material is viscoelastic, with temperature-dependent dislocation creep. We solve the heat equation for temperature, accounting for frictional and viscous shear heating that creates a thermal anomaly relative to the ambient geotherm which reduces viscosity and facilitates viscous flow. We explore several geotherms and effective normal stress distributions (by changing pore pressure), quantifying the thermal anomaly, seismic and aseismic slip, and the transition from frictional sliding to viscous flow. The thermal anomaly can reach several hundred degrees below the seismogenic zone in models with hydrostatic pressure, but is smaller for higher pressure (and these high-pressure models are most consistent with San Andreas Fault heat flow constraints). Shear heating raises the BDT, sometimes to where it limits rupture depth rather than the frictional VW-to-VS transition. Our thermomechanical modeling framework can be used to evaluate lithospheric rheology and thermal models through predictions of earthquake ruptures, postseismic and interseismic crustal deformation, heat flow, and the geological structures that reflect the complex deformation beneath faults.

We reveal a slip-partitioning rupture on the North Hovsgol Fault during the 2021 Mw6.7 Lake Hovsgol, Mongolia earthquake. Left-lateral motions on the Mondy Fault north of the epicenter likely controlled the observed slip partitioning pattern. The earthquake highlights the non-negligible role of the bounding strike-slip fault in the formation and evolution of oblique rift.

Hourly precipitation extremes can intensify with temperature at higher rates than expected from thermodynamic increases explained by the Clausius-Clapeyron (CC) relationship (~6.5%/K), but local scaling with surface air temperature is highly variable. Here we use daily dewpoint temperature, a direct proxy of absolute humidity, to estimate at-gauge local scaling across six macro-regions for a global dataset of over 7000 hourly precipitation gauges. We find scaling rates from CC to 2xCC at more than 60% of gauges, peaking in the tropics at a median rate of ~1.5CC. Moreover, regional scaling rates show surprisingly universal behaviour at around CC, with higher scaling in Europe. Importantly for impacts, hourly scaling is persistently higher than scaling for daily extreme precipitation. Our results indicate greater consistency in global scaling than previous work, usually at or above CC, with positive scaling in the (sub)tropics. This demonstrates the relevance of dewpoint temperature scaling to understanding future changes.

In stratified flow, breaking of internal waves over slopes induces resuspension of bottom sediments and transport of mass. When internal waves shoal and break, flow dynamics and mass transport differ greatly according to whether the Coriolis force is included or neglected. Despite its importance, the currents generated by breaking internal Kelvin waves remain uninvestigated. Therefore, this study considers breaking of internal waves over a uniform slope under Coriolis with equivalent upper- and lower-layer depths. Laboratory experiments, using a 6.0 m rotating tank, were undertaken to visualize currents using Particle Image Velocimetry. Experimental data validated a three-dimensional fluid dynamics model, in-which a coastal-jet was simulated to occur at the lateral wall (to the right) of the progressive internal Kelvin waves in the breaking zone; with generation of an oblique downslope return flow (downdraft) under Coriolis. The coastal-jet was driven by the geostrophic balance, and the equation for estimating the residual current, due to the jet, was formulated. The results provide insight on mass transport in lakeshore and coastal zones.