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 (NOx), 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.
Explosive volcanic eruptions inject hot mixtures of solid particles (tephra) and gasses into the atmosphere. Entraining ambient air, these mixtures can form plumes rising tens of kilometers until they spread laterally, forming umbrella clouds. While the largest clasts tend to settle in proximity to the volcano, the smallest fragments, commonly referred to as ash (≤2 mm in diameter), can be transported over long distances, forming volcanic clouds. Tephra plumes and clouds pose significant hazards to human society, affecting infrastructure, and human health through deposition on the ground or airborne suspension at low altitudes. Additionally, volcanic clouds are a threat to aviation, during both high-risk actions such as take-off and landing and at standard cruising altitudes. The ability to monitor and forecast tephra plumes and clouds is fundamental to mitigate the hazard associated with explosive eruptions. To that end, various monitoring techniques, ranging from ground-based instruments to sensors on-board satellites, and forecasting strategies, based on running numerical models to track the position of volcanic clouds, are efficiently employed. However, some limitations still exist, mainly due to the high unpredictability and variability of explosive eruptions, as well as the multiphase and complex nature of volcanic plumes. In the next decades, advances in monitoring and computational capabilities are expected to address these limitations and significantly improve the mitigation of the risk associated with tephra plumes and clouds.
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