AGU Advances最新文献

The 2023 East Asian summer experienced a record-breaking compound hot-humid extreme and an unprecedented concurrent marine heatwave (MHW) in surrounding oceans. Understanding and quantifying the impacts of such MHWs on land heatwaves can enhance seasonal prediction skills for these extremes. Here we evaluate the impact of the 2023 MHW on the record-breaking atmospheric heatwave in East Asia during the summer. Through a set of regional atmospheric model experiments, we demonstrate that the MHW significantly exacerbated the 2023 East Asian summer atmospheric heatwave, particularly as a compound hot-humid extreme. The extremely warm ocean amplified both surface air temperature and humidity anomalies, on top of the contributions of background atmospheric circulation anomalies. The MHW influence on air temperature manifests through radiative effects of cloud and water vapor changes. Our results also indicate that the atmospheric heatwave amplifies despite the MHW acts to dampen the western North Pacific subtropical high against large-scale background atmospheric conditions. By examining the effects of both temperature and humidity anomalies through wet-bulb globe temperature, we find that the MHW explains ∼20%–50% of the aggravation and prolonged duration of hot-humid conditions in East Asia, with notable impacts in Japan. Additionally, the recent trend of sea surface warming is shown to substantially amplify the MHW's impact on the heatwave. Our findings underscore the key role of ocean variability and air–sea interactions in surrounding oceans on atmospheric heatwaves that occur in the summer climate in East Asia, highlighting a unique process in the humid and low cloud-abundant maritime East Asia region.

The properties and rheology of subduction zones have been intensively studied to forecast potential megathrust earthquake scenarios. However, in Cascadia, the absence of recent megathrust events limits available seismic evidence. Tectonic tremors occurring downdip of the megathrust provide valuable insights into stress accumulation and propagation and can help constrain stress states and rheology. We build upon a previous method to extract tremor migrations in a large catalog of ∼330,000 tremors, addressing location errors and temporal resolution of the catalog, which are particularly crucial for this region. The spatiotemporally dense tremor activity identified by our improved method, along with the greatly increased number of extracted migrations (∼13,700), facilitates a more quantitative analysis. Our findings suggest that tremor migration is primarily controlled by stress diffusion in a medium exhibiting viscous behavior rather than fluid diffusion. The observed relationship between migration speed and duration implies a diffusivity of 10³–10⁵ m²/s, and aligns with a simple model indicating an approximately 30-km-wide zone of slow slip and tremor propagation. Additionally, we identify three along-strike barriers to tremor migrations, consistent with previously identified segments persisting from shallow to deep. Notably, the barrier near 48.5°N consistently decelerates, terminates, or initiates large tremor episodes, likely due to geometric distortions, including flattening and bending of the slab. In contrast, a barrier near 42.5°N abruptly halts migrations and accumulates stress, but can be breached by sufficient stress perturbation. Thus, tremor migrations can constrain geometric segmentation and diffusive behavior of tremorgenic regions from a dynamic perspective.

Understanding the interplay of various energy sinks during seismic fault slip is essential for advancing earthquake physics and improving hazard assessment. However, quantifying the energy consumed by major dissipative processes remains a challenge. In this study, we investigate energy partitioning during laboratory earthquakes (“lab-quakes”) by performing general shear stick-slip experiments on synthetic granitic cataclasites at elevated confining pressure. Using ultrasound, microstructural, and novel magnetism-based thermal analyses, we independently quantified the energy allocated to seismic radiation, new surfaces, and heat dissipation. These estimates showed good agreement with far-field measurements of mechanical work during the lab-quake. Our findings revealed that under the experimental conditions the majority of the released energy (68%–98%) is dissipated as heat, while seismic radiation accounts for 1%–8%, and the creation of new surfaces consumes <1%–32%. Microstructural observations indicate pre-failure deformation, which includes comminution and development of the principal slip zone, significantly influences energy partitioning. This effect is further evident in the measured shear stress drops, where events with higher stress drops proportionally emitted more energy as seismic waves. This study is the first to constrain the full energy budget of lab-quakes from an observational standpoint, providing critical insights into the dynamics of fault rupture and energy dissipation processes.

A key challenge for computationally intensive state-of-the-art Earth System models is to distinguish global warming signals from interannual variability. Here we introduce Deep Learning Earth System Model (DLESyM), a parsimonious deep learning model that accurately simulates the Earth's current climate over 1000-year periods with minimal smoothing and no drift. DLESyM simulations equal or exceed key metrics of seasonal and interannual variability—such as tropical cyclogenesis over the range of observed intensities, the cycle of the Indian Summer monsoon, and the climatology of mid-latitude blocking events—when compared to historical simulations from four leading models from the sixth Climate Model Intercomparison Project. DLESyM, trained on both historical reanalysis data and satellite observations, is an accurate, highly efficient model of the coupled Earth system, empowering long-range sub-seasonal and seasonal forecasts while using a fraction of the energy and computational time required by traditional models.

Permafrost, a critical global cryospheric component, supports subarctic boreal forests but is frequently disturbed by wildfires, an important driver of permafrost degradation. Wildfires reduce vegetation, organic layers, and surface albedo, leading to active layer thickening and ground subsidence. Recent studies using interferometric synthetic aperture radar (InSAR) have confirmed the rapid and extensive post-fire permafrost degradation, and have largely focused on short-term impacts. However, the longer-term post-fire permafrost deformation, potentially persisting for decades, remains poorly understood due to limited data. Here, we applied InSAR in North Yukon to detect deformation signals across multiple fire scars in the past five decades. Using a chronosequence (space-for-time substitution) approach, we summarize a continuous trajectory of post-fire permafrost evolution: (a) an initial degradation stage, characterized by abrupt subsidence up to 50 mm/year and gradually slowing over the first decade, with cumulative subsidence exceeding 100 mm locally; (b) an aggradation stage from approximately 15 to 30 years after fire, marked by ground uplift reaching 25 mm/year before gradually declining, compensating for the earlier subsidence; and (c) a stabilization stage beyond three to four decades, where permafrost nearly recovers to pre-fire conditions with indistinguishable deformation between burned and unburned areas. Notably, the rarely-reported uplift phase appears closely related to vegetation regeneration and fire-greening feedback that provide thermal protection, suggesting a critical mechanism of permafrost recovery. These findings provide new insights into the resilience of boreal-permafrost systems to wildfires and also underscore the importance of long-term InSAR monitoring in understanding permafrost responses to wildfires under climate change.

The recent U.S. executive order “Restoring Gold Standard Science” poses a significant threat to the U.S. national economy and security. The order replaces the scientific experts who lead U.S. governmental scientific organizations with non-scientific political appointees who would have the power to decide what science could and could not be published. In doing so, the executive order threatens to reverse more than 80 years of scientific advancements that have given the U.S. its world-leading military, technology, and economy. The justifications provided in the executive order for this change in policy are false or misleading in their assessment and representation of the current state of U.S. scientific scholarship. Hypocritical in its aims, the executive order claims to promote integrity in science while at the same time calling to remove the “Framework for Federal Scientific Integrity Policy and Practice” that currently ensure veracity and credibility in science. The executive order is also unconstitutional, threatening to take away the First Amendment rights of scientists by punishing them if they publish truthful and accurate science that is contrary to the administration's political agenda. Such censorship of scientists has been attempted by failed governments of the past such as Nazi Germany, the Soviet Union, and early communist China, always with disastrous consequences for their citizens. “Restoring Gold Standard Science” needs to be rescinded to avoid catastrophic consequences for the U.S. economy and national security.

Numerous proposed geoengineering schemes to mitigate climate change and its consequences are now widely discussed in the scientific literature. Sea level rise is a clear example of the implications of climate change with a further committed rise of at least 2–3 m embedded within the Earth System from +1.5°C of global warming. A bold suggestion to reduce sea level rise is to install underwater barriers to reduce the inflow of oceanic heat around Antarctica and Greenland. Inflow of warm, saline water masses drives ice melt and the destabilization of tidewater glaciers. Whilst the basic theory that barriers would stem oceanic heat flow is uncontroversial, the extent to which barriers might reduce future ice mass loss is less certain. There are numerous concerns about the viability and side-effects of this proposed intervention. We use existing field observations and representative fjord-scale models for the Greenland's largest glacier, Sermeq Kujalleq in the Ilulissat Icefjord, to suggest that there is already sufficient evidence to conclude that artificial barrier installation would have negative regional implications for marine productivity. The effects on fisheries are a concern as negative implications for Greenland's regional fisheries are unlikely to be socially acceptable. Increasing “geoengineeringization” of the Earth Sciences is likely to continue in coming decades as society grapples with the challenges of slowing climate change and mitigating its consequences. To produce beneficial results, the technical and social viabilities of geoengineering concepts need to be considered in parallel, with the latter determined in a complex social, economic and cultural nexus.

Summertime spatially compound climate extremes in the Northern Hemisphere are associated with dominant jet stream Rossby wavenumber patterns, including wavenumber5 (wave5). However, our knowledge of wave5, including its response to anthropogenic warming, is limited by the short length of instrumental records of upper-level fields. To provide a longer-term perspective, we present a 1,000-year reconstruction of a wave5 pattern that modulates summertime compound extremes, constructed by targeting drought anomalies associated with this pattern in three regions. Our results show no major trends in the occurrence of this pattern over the past millennium. We further show that La Niña winters often precede a wave5 event the following summer, evident over centuries. This pattern was exemplified by the La Niña winter of 2022–2023, which was followed by wave5-driven compound heatwaves in July. The imprint of continued anthropogenic warming on ENSO may exacerbate wave5-driven extremes, especially if the tropical Pacific becomes more La Niña-like.

High Mountain Asia (HMA) plays a crucial role in Asian hydrology—its vast snow and glacier-covered landscape significantly influences downstream river water supply for billions of people. Understanding the spatiotemporal pattern of river discharge in HMA aids effective water resource management and infrastructure planning. In this study, we used a combination of hydrologic modeling and assimilation of remotely sensed discharge from Landsat and PlanetScope imagery to investigate how daily river discharge has changed for more than 114,000 reaches across HMA between 2004 and 2019. We observed significant increasing trends in river discharge for 11,113 reaches (∼10%), particularly in smaller rivers of the Syr Darya, Indus, Yangtze, and Yellow River basins. The ratio of total glacial melt and precipitation received by individual river reach showed an average significant increase of 2.2% per year, particularly in the Syr Darya, Amu Darya and Western Indus rivers. Across HMA, our results also indicate that 8% of river reaches with either planned and existing hydropower plants or dams experienced a statistically significant average increase of 2.9% per year in stream power. These findings illustrate the rapidly changing patterns of river discharge and stream power in HMA.

Mercury underwent global contraction due to the sustained cooling of the planet. Positive-relief landforms, found widespread across Mercury, are thought to be the surface expressions of thrust faults accommodating the contraction. Disagreement exists in the literature on the amount of contraction, with estimates of radius change ranging from ∼1 to 7 km. These differences solely arise from the method used to estimate the fault population strain, which relies on the number of structures. Here, we adapt a previous framework by which the continuum approximation to shortening strains can be determined from fault length and displacement statistics for an incompletely sampled fault population. We apply this method to three data sets that sample different numbers of faults. Our results show that even for conservative fault parameters, 2 to 3.5 km of radial contraction are returned, irrespective of the data set used, and thus resolve the debate on the amount of global contraction on Mercury.