Reviews of Geophysics最新文献

Physical and chemical erosion associated with water both affect land–atmosphere carbon exchanges. However, previous studies have often addressed these processes separately or used oversimplified mechanisms, leading to ongoing debates and uncertainties about erosion-induced carbon fluxes. We provide an overview of the on-site carbon uptake fluxes induced by physical erosion (0.05–0.29 Pg C yr⁻¹, globally) and chemical erosion (0.26–0.48 Pg C yr⁻¹). Then, we discuss off-site carbon dynamics (during transport, deposition, and burial). Soil organic carbon mineralization during transport is nearly 0.37–1.20 Pg C yr⁻¹ on the globe. We also summarize the overall carbon fluxes into estuaries (0.71–1.06 Pg C yr⁻¹) and identify the sources of different types of carbon within them, most of which are associated with land erosion. Current approaches for quantifying physical-erosion-induced vertical carbon fluxes focus on two distinct temporal scales: short-term dynamics (ranging from minutes to decades), emphasizing net vertical carbon flux, and long-term dynamics (spanning millennial to geological timescales), examining the fate of eroded carbon over extended periods. In addition to direct chemical measurement and modeling approaches, estimation using indicators of riverine material is popular for constraining chemical-erosion-driven carbon fluxes. Lastly, we highlight the key challenges for quantifying related fluxes. To overcome potential biases in future studies, we strongly recommend integrated research that addresses both physical and chemical erosion over a well-defined timescale. A comprehensive understanding of the mechanisms driving erosion-induced lateral and vertical carbon fluxes is crucial for closing the global carbon budget.

The significance of crop evapotranspiration (ET_a) to climate science, agronomic research, and water resources is not in dispute. What continues to draw attention is how variability in ET_a is driven by changing environments, abiotic stresses, and management practices. Here, the impacts of elevated CO₂ concentration (e[CO₂]), elevated ozone concentration (e[O₃]), warming, abiotic stresses (water, salinity, heat stresses), and management practices (planting density, irrigation methods, mulching, nitrogen application) on cropland ET_a were reviewed, along with their possible causes and estimation. Water and salinity stresses, e[O₃], and drip irrigation adoption generally led to lower total growing–season ET_a. However, total growing–season ET_a responses to e[CO₂], warming, heat stress, mulching, planting density, and nitrogen supplement appear inconsistent across empirical studies. The effects of e[CO₂], e[O₃], water and salinity stresses on total growing–season ET_a are attributed to their influence on stomatal conductance, root water uptake, root and leaf area development, microclimate, and potentially phenology. Total growing–season ET_a in response to warming is affected by variations in ambient growing–season mean air temperature and phenology. The differences in crop ET_a under varying planting densities are due to their differences in leaf area. The responses of ET_a to heat stress, mulching, and nitrogen application represent trade–off between their opposite effects on transpiration and evaporation, along with possibly phenology. Modified ET_a models currently in use can estimate the response of ET_a to the many aforementioned factors except for e[O₃], heat stress, and nitrogen application. These factors offer a blueprint for future research inquiries.

Asian megadeltas, specifically the Ganges-Brahmaputra-Meghna, Irrawaddy, Chao Phraya, Mekong, and Red River deltas host half of the world's deltaic population and are vital for Asian countries' ecosystems and food production. These deltas are extremely vulnerable to global change. Accelerating relative sea-level rise, combined with rapid socio-economic development intensifies these vulnerabilities and calls for a comprehensive understanding of current and future coastal flood dynamics. Here we provide a state-of-the-art on the current knowledge and recent advances in quantifying and understanding the drivers of coastal flood-related hazards in these deltas. We discuss the environmental and physical drivers, including climate influence, hydrology, oceanography, geomorphology, and geophysical processes and how they interact from short to long-term changes, including during extreme events. We also jointly examine how human disturbances, with catchment interventions, land use changes and resource exploitations, contribute to coastal flooding in the deltas. Through a systems perspective, we characterize the current state of the deltaic systems and provide essential insights for shaping their sustainable future trajectories regarding the multifaceted challenges of coastal flooding.

Dramatic reductions in anthropogenic emissions during the lockdowns of the COVID-19 pandemic provide an unparalleled opportunity to assess responses of the Earth system to human activities. Here, we synthesize the latest progress in understanding changes in short-lived atmospheric constituents, that is, aerosols, ozone (O₃), nitrogen oxides (NO_x), and methane (CH₄), in response to COVID-19 induced emission reductions and the associated climate impacts on regional and global scales. The large-scale emission reduction in the transportation sector reduced near-surface particulate and ozone concentrations, with certain regional enhancements modulated by atmospheric oxidizing capacity and abnormal meteorological conditions. The methane increase during the pandemic is a combined effect of fluctuations in methane emissions and chemical sinks. Global net radiative forcing of all short-lived species was found to be small, but regionally, aerosol radiative impacts during the lockdowns were discernible near China and India. Aerosol microphysical effects on clouds and precipitation were reported from modeling assessments only, except for observed reductions in aircraft contrails. There exist moderate climatic impacts of the pandemic on regional surface temperature, atmospheric circulations, and ecosystems, mainly over populous and polluted areas. Novel methodologies emerge in the pandemic-related research to achieve the synergy between observations from multiple platforms and model simulations and to overcome the enormous hurdles and sophistication in detection and attribution studies. The insight gained from COVID-19 research concerning the complex interplay between emission, chemistry, and meteorology, as well as the unexpected climate forcing-responses relationships, underscores future challenges for cleaning up the air and alleviating the adverse impacts of global warming.

Mineral carbon storage in mafic and ultramafic rock masses has the potential to be an effective and permanent mechanism to reduce anthropogenic CO₂. Several successful pilot-scale projects have been carried out in basaltic rock (e.g., CarbFix, Wallula), demonstrating the potential for rapid CO₂ sequestration. However, these tests have been limited to the injection of small quantities of CO₂. Thus, the longevity and feasibility of long-term, large-scale mineralization operations to store the levels of CO₂ needed to address the present climate crisis is unknown. Moreover, CO₂ mineralization in ultramafic rocks, which tend to be more reactive but less permeable, has not yet been quantified. In these systems, fractures are expected to play a crucial role in the flow and reaction of CO₂ within the rock mass and will influence the CO₂ storage potential of the system. Therefore, consideration of fractures is imperative to the prediction of CO₂ mineralization at a specific storage site. In this review, we highlight key takeaways, successes, and shortcomings of CO₂ mineralization pilot tests that have been completed and are currently underway. Laboratory experiments, directed toward understanding the complex geochemical and geomechanical reactions that occur during CO₂ mineralization in fractures, are also discussed. Experimental studies and their applicability to field sites are limited in time and scale. Many modeling techniques can be applied to bridge these limitations. We highlight current modeling advances and their potential applications for predicting CO₂ mineralization in mafic and ultramafic rocks.

Globally, land subsidence (LS) often adversely impacts infrastructure, humans, and the environment. As climate change intensifies the terrestrial hydrologic cycle and severity of climate extremes, the interplay among extremes (e.g., floods, droughts, wildfires, etc.), LS, and their effects must be better understood since LS can alter the impacts of extreme events, and extreme events can drive LS. Furthermore, several processes causing subsidence (e.g., ice-rich permafrost degradation, oxidation of organic matter) have been shown to also release greenhouse gases, accelerating climate change. Our review aims to synthesize these complex relationships, including human activities contributing to LS, and to identify the causes and rates of subsidence across diverse landscapes. We primarily focus on the era of synthetic aperture radar (SAR), which has significantly contributed to advancements in our understanding of ground deformations around the world. Ultimately, we identify gaps and opportunities to aid LS monitoring, mitigation, and adaptation strategies and guide interdisciplinary efforts to further our process-based understanding of subsidence and associated climate feedbacks. We highlight the need to incorporate the interplay of extreme events, LS, and human activities into models, risk and vulnerability assessments, and management practices to develop improved mitigation and adaptation strategies as the global climate warms. Without consideration of such interplay and/or feedback loops, we may underestimate the enhancement of climate change and acceleration of LS across many regions, leaving communities unprepared for their ramifications. Proactive and interdisciplinary efforts should be leveraged to develop strategies and policies that mitigate or reverse anthropogenic LS and climate change impacts.

Age of stratospheric air is a well established metric for the stratospheric transport circulation. Rooted in a robust theoretical framework, this approach offers the benefit of being deducible from observations of trace gases. Given potential climate-induced changes, observational constraints on stratospheric circulation are crucial. In the past two decades, scientific progress has been made in three main areas: (a) Enhanced process understanding and the development of process diagnostics led to better quantification of individual transport processes from observations and to a better understanding of model deficits. (b) The global age of air climatology is now well constrained by observations thanks to improved quality and quantity of data, including global satellite data, and through improved and consistent age calculation methods. (c) It is well established and understood that global models predict a decrease in age, that is, an accelerating stratospheric circulation, in response to forcing by greenhouse gases and ozone depleting substances. Observational records now confirm long-term forced trends in mean age in the lower stratosphere. However, in the mid-stratosphere, uncertainties in observational records are too large to confirm or disprove the model predictions. Continuous monitoring of stratospheric trace gases and further improved methods to derive age from those tracers will be crucial to better constrain variability and long-term trends from observations. Future work on mean age as a metric for stratospheric transport will be important due to its potential to enhance the understanding of stratospheric composition changes, address climate model biases, and assess the impacts of proposed climate geoengineering methods.

Geothermal energy is a green source of power that could play an important role in climate-conscious energy portfolios; enhanced geothermal systems (EGS) have the potential to scale up exploitation of thermal resources. During hydraulic fracturing, fluids injected under high-pressure cause the rock mass to fail, stimulating fractures that improve fluid connectivity. However, this increase of pore fluid pressure can also reactivate pre-existing fault systems, potentially inducing earthquakes of significant size. Induced earthquakes are a significant concern for EGS operations. In some cases, ground shaking nuisance, building damages, or injuries have spurred the early termination of projects (e.g., Basel, Pohang). On the other hand, EGS operations at Soultz-sous-Forêts (France), Helsinki (Finland), Blue Mountain (Nevada, USA), and Utah FORGE (USA) have adequately managed induced earthquake risks. The success of an EGS operation depends on economical reservoir enhancements, while maintaining acceptable seismic risk levels. This requires state-of-the-art seismic risk management. This article reviews domains of seismology, earthquake engineering, risk management, and communication. We then synthesize “good practice” recommendations for evaluating, mitigating, and communicating the risk of induced seismicity. We advocate for a modular approach. Recommendations are provided for key technical aspects including (a) a seismic risk management framework, (b) seismic risk pre-screening, (c) comprehensive seismic hazard and risk evaluation, (d) traffic light protocol designs, (e) seismic monitoring implementation, and (f) step-by-step communication plans. Our recommendations adhere to regulatory best practices, to ensure their general applicability. Our guidelines provide a template for effective earthquake risk management and future research directions.

Soil salinization refers to the accumulation of water-soluble salts in the upper part of the soil profile. Excessive levels of soil salinity affects crop production, soil health, and ecosystem functioning. This phenomenon threatens agriculture, food security, soil stability, and fertility leading to land degradation and loss of essential soil ecosystem services that are fundamental to sustaining life. In this review, we synthesize recent advances in soil salinization at various spatial and temporal scales, ranging from global to core, pore, and molecular scales, offering new insights and presenting our perspective on potential future research directions to address key challenges and open questions related to soil salinization. Globally, we identify significant challenges in understanding soil salinity, which are (a) the considerable uncertainty in estimating the total area of salt-affected soils, (b) geographical bias in ground-based measurements of soil salinity, and (c) lack of information and data detailing secondary salinization processes, both in dry- and wetlands, particularly concerning responses to climate change. At the core scale, the impact of salt precipitation with evolving porous structure on the evaporative fluxes from porous media is not fully understood. This knowledge is crucial for accurately predicting soil water loss due to evaporation. Additionally, the effects of transport properties of porous media, such as mixed wettability conditions, on the saline water evaporation and the resulting salt precipitation patterns remain unclear. Furthermore, effective continuum equations must be developed to accurately represent experimental data and pore-scale numerical simulations.