Recent studies have found a dipole pattern of hydroclimate variation in western Asia (WA) and arid central Asia (ACA) during the Holocene. However, speleothem delta O-18 evidence shows some inconsistencies with other lines of evidence, especially concerning the timing of peak wetness in WA and precipitation trends in ACA. In an attempt to investigate these discrepancies, we employ the transient isotope-enabled simulation, that is, the iTraCE experiment, and water tagging sensitivity experiments driven by high and low precessions. The relationship between variations in water isotopes and precipitation and the underlying mechanisms are investigated. We find trends toward enriched delta O-18 over three regions, with decreasing precipitation over WA and western central Asia (WCA) but increasing precipitation over eastern central Asia (ECA) during the Holocene. These opposing relationships between delta O-18 and precipitation result from a number of different mechanisms. The delta O-18(p) enrichments over WA, WCA, and ECA arise mainly from the Indian Ocean and Africa, North Atlantic Ocean, and Pacific Ocean source regions, respectively. These delta O-18(p) enrichments result more from decreases of precipitation weight sourced from these regions than from increases of isotope ratio through the source and en route effects. These precipitation weight decreases and isotope ratio increases are tied to precession-driven changes in large-scale circulation, including the African monsoon weakening, winter polar front westerly jet weakening, summer subtropical westerly jet strengthening, and Asian monsoon weakening.

We employ a semiempirical approach combining climate model simulations and observational temperatures to assess the likelihood of recent global temperature records. Monte Carlo simulations are used to generate global temperature series consistent with combined estimates of forced (anthropogenic + natural) and internal variability derived from observations and CMIP6 multimodel simulations. We find that the El Niño-boosted 2024 global temperature record had a ~12% likelihood of occurrence (a one-in-eight-year event), similar to the prior (also El Niño-boosted) record year 2016 (~14% likelihood). Of the records set during the past three decades, only 1998 is found to have been truly anomalous, with a ~2.5% likelihood of occurrence. Each of these records is found to have been nearly impossible in the absence of human-caused warming.

The Atlantic Meridional Overturning Circulation (AMOC) is a key component of our climate system. However, the evolution history and the forcing mechanism of AMOC in the last millennial has remained uncertain. Here, combining available paleo AMOC-sensitive indicators with multiple climate models and paleo Data Assimilation, we show, for the first time, that the AMOC transport exhibits a slow declining trend into the Little Ice Age, with a reduction of about - 0.7 ± 0.4 S v . (~4%) from AD 850-1850. This weakening is mainly caused by explosive volcanic eruptions. After a rapid strengthening in the initial decade following a volcanic eruption, the AMOC tends to show a slow weakening of centennial timescale, driven by stored cooling in the deep Atlantic and its feedback on North Atlantic climate.

Global ocean warming continued unabated in 2025 in response to increased greenhouse gas concentrations and recent reductions in sulfate aerosols, reflecting the long-term accumulation of heat within the climate system, with conditions evolving toward La Niña during the year. In 2025, global upper 2000 m ocean heat content (OHC) increased by ∼23 ± 8 ZJ relative to 2024 according to IAP/CAS estimates. CIGAR-RT, and Copernicus Marine data confirm the continued ocean heat gain. Regionally, about 33

Volcanic eruptions are among the most profound sources of natural external radiative forcing of the climate system, imparting significant impacts on global and regional climate. Previous studies have established that explosive volcanic forcing induced substantial multidecadal (∼50–70-year timescale) variability in global mean temperature during the last millennium. The consequences for other climate subsystems remain largely unexplored. In this study, volcanic forcing-induced multidecadal variability of the Northern Hemisphere land monsoon (NHLM) and sub-monsoon precipitation is examined through comparison between climate model simulations and speleothem δ18O climate proxy records. We find that volcanic forcing plays a long-term role in modulating the NHLM system and associated precipitation on multidecadal timescales. This variability, however, is consistently found in both proxy records and model simulations, to be intermittent. Volcanic-induced multidecadal variability is observed in the North African monsoon region between 1150 and 1300, while the South Asian monsoon is strongly influenced between 1750 and 1850. In contrast, the East Asian monsoon precipitation exhibits multidecadal variability not directly caused by volcanic eruptions, and the America monsoon region shows no clear volcanic response. These differences can be attributed to the nonlinear, threshold-based responses of sub-monsoon systems to volcanically induced radiative forcing, with responses to weaker forcing indistinguishable from internal variability. Our findings highlight the important, but somewhat complex, linkage between natural volcanic radiative forcing and the response of certain subsystems, such as the NHLM and associated precipitation, to that forcing.

Hurricane Ida struck the U.S. East Coast in August 2021, driving the Schuylkill River in Philadelphia to a record discharge nearly 100 times its average flow. Ida exposes the growing challenge of predicting urban flooding arising from coupled rainfall–runoff and river–tide–landscape interactions that coarse models cannot resolve. Here, we address this gap with a street-resolving flood model that integrates LiDAR-derived terrain, bathymetric surveys, and land-use-based surface friction across Philadelphia’s watershed to reproduce Ida’s flood. We show that soil saturation, impervious surfaces, and fragmented infrastructure amplify pluvial flooding, increasing exposure in both low- and high-income communities. Scenario simulations reveal a flood tipping point: for river return periods exceeding 100 years, the inundated area grows logarithmically, with an additional 2–7% increase in flooding when peak discharge coincides with high tide and up to $$\sim$$ 15% under projected sea-level rise by 2100. As extreme rainfall intensifies and return periods shorten, this tipping point will be crossed more often, demanding integrated forecasting and adaptive planning in vulnerable, low-lying, rapidly urbanizing regions.

Abstract For a long time, the 4.2 ka event was considered sufficiently significant to mark the onset of the Meghalayan Age, the latest stage of the Holocene. However, the spatial distribution and temporal evolutions of precipitation changes remain controversial in many regions, especially in monsoon Asia. In this study, combining the high‐resolution speleothem calcite oxygen isotope ratio value (δ 18 O c ) records and the transient simulation of an isotope enabled earth system model, we reconstruct the spatiotemporal evolution of δ 18 O c and precipitation in the Asian monsoon region during the 4.2 ka event (4.3–3.9 ka BP) with 10‐year temporal resolution and 2.5° × 1.9° spatial resolution, using an offline ensemble Kalman filter. Based on these reconstructed results, we analyze the characteristics of the 4.2 ka event over monsoon Asia from two aspects. On the centennial scale, the event shows a drought pattern in northern China and South Asia, and a wet pattern in southern China. On the multi‐decadal scale, frequent wet‐dry excursions occur in the region. Notably, both the centennial‐scale changes and multi‐decadal excursions largely fall within the range of Holocene natural variability. These results challenge the conventional view of the 4.2 ka event as a global megadrought and instead suggest that, even within monsoon Asia, it was expressed as a spatially heterogeneous hydroclimatic anomaly rather than a spatially uniform or exceptionally extreme event.

Nor'easters are coastal extratropical cyclones that feed upon both thermal contrasts (meridional and land-ocean) and oceanic latent heat release, causing them to intensify along the U.S. East Coast. With central pressures that sometimes rival those of tropical cyclones, they represent a significant coastal hazard and are often associated with strong winds, heavy snowfall, disruption, and damage. While interest in studying the impacts of climate change on storm behavior is growing, nor'easters have historically received far less attention than tropical cyclones, largely due to challenges in documenting and categorizing these storms combined with the relatively short observational record. Here, we address these challenges by employing a cyclone tracking approach in concurrence with long-term reanalysis data to create a reliable historical database of these storms. We find a significant increasing trend in the maximum wind speeds of the most intense (>66th percentile) nor'easters. We also observe an increasing trend in hourly precipitation rates associated with these storms. Such changes have profound implications for coastal cities and shorelines, increasing the risk of coastal flooding and erosion.

People do not have to dismiss or exaggerate the climate threat to justify concerted action. People do not have to dismiss or exaggerate the climate threat to justify concerted action.

We demonstrate a tripling in the frequency of planetary wave resonance events over the past halfcentury, coinciding with the rise in persistent boreal summer weather extremes. This increase aligns with changes in the underlying climate conditions favoring these events, including amplified Arctic warming and land–sea thermal contrast. We also observe increased prevalence of resonant amplification events following the mature phase of strong El Niño events, suggesting that such events may precondition the mean state conditions in ways that favor large-scale quasi-stationary wave patterns and quasi-resonant wave amplification. Since the impact of anthropogenic warming on quasi-resonant amplification is not well captured by current-generation climate models, it is likely that models are underpredicting the potential increase, indicating even greater risk of persistent extreme summer weather events with ongoing warming.

Heating in the ocean has continued in 2024 in response to increased greenhouse gas concentrations in the atmosphere, despite the transition from an El Niño to neutral conditions. In 2024, both global sea surface temperature (SST) and upper 2000 m ocean heat content (OHC) reached unprecedented highs in the historical record. The 0–2000 m OHC in 2024 exceeded that of 2023 by 16 ± 8 ZJ (1 Zetta Joules = 1021 Joules, with a 95

Mitigating climate change requires urgent action at individual, collective, and institutional levels. However, individuals may fail to act because they perceive climate change as a threat that is distant or not personally relevant, or believe their actions are not impactful. To address these psychological barriers, we conducted a large-scale "intervention tournament." In a sample of 7,624 participants, we systematically tested 17 interventions that targeted psychological mechanisms described by three key themes: Relevance, Future Thinking, and Response Efficacy. Interventions that emphasized social relevance were the most effective for motivating people to share news articles and petitions about climate change. Interventions that targeted future thinking were the most effective for broadly motivating individual actions (e.g., driving less, eating vegetarian meals) and collective actions (e.g., donating, volunteering) to address climate change. Interventions that emphasized the environmental impact of these actions reliably increased the perceived impact of pro-environmental actions, but did not consistently motivate action. Notably, interventions that targeted two or more mechanisms-such as imagining a future scenario that involved oneself or close others-were most effective. Importantly, our leading interventions were substantially more effective than prevalent existing strategies (e.g., carbon footprint information). Our findings are relevant to theories of behavior change, motivation, and information sharing, with potential applications across domains. Insights from our tournament could be applied to develop scalable online interventions and mass communication campaigns to address climate change.

The Earth system model CLIMBER-2 has been used in past work to successfully reproduce the glacial/interglacial cycles of the Plio-Pleistocene and the Mid-Pleistocene Transition (MPT) from predominantly 40 to 100 ky timescale oscillatory behavior as a function of declining volcanic outgassing and regolith removal. In this study, we further examine the sensitivity of this previous work to varying prescribed levels of volcanic outgassing and regolith extent and the long-term dynamics of the global carbon cycle, affecting the exchange and partitioning of carbon between different Earth system reservoirs and therefore global atmospheric CO2 concentrations. As volcanic outgassing decreases, CO2 and land carbon storage decrease, while ocean carbon storage, including CaCO3 sediment, increases. At volcanic outgassing levels below a threshold value of roughly 5.7 Tmol C yr-1, sea level decreases due to land ice formation, leading to increased carbon accumulation in the ocean and decreased carbon in the CaCO3 sediment reservoir. Our previous finding of strong hysteresis and path dependence in the glacial/interglacial alternation history [J. Carrillo et al., Proc. Natl. Acad. Sci. 121, e2322926121 (2024)] appears to be a tenuous climate feature, dependent on the precise representation of carbon cycle processes and, specifically, the numerical precision used in the calculation of certain key state variables in the model's carbon cycle.

Annual North Atlantic tropical cyclone (TC) counts are frequently modeled as a Poisson process with a state‐dependent rate. Current models based on Poisson regression can explain roughly 50% of the annual variance using three climate indices: El Niño/Southern Oscillation, average sea surface temperature (SST) in the main development region of the North Atlantic, and the North Atlantic oscillation atmospheric circulation index. We introduce a new method, based on the Elastic Net (EN) that predicts TC counts directly from global SST maps. We show it achieves performance on par with current models, without requiring manually constructed indices. To understand the performance of the EN we argue that, when TC counts are generated by independent Poisson draws, statistical models are subject to a lower limit on prediction error. We estimate this limit and show that it is saturated by both current models and our new method.

Evolving tropical cyclone characteristics are expected to amplify coastal hazards in a warmer climate. Here, we investigated seasonal-scale tropical cyclone genesis and landfall patterns from >64,000 statistically-downscaled tropical cyclones that impact Southeast Asian coastlines from the historical (1881-1900) through the future (2081-2100) eras for both moderate and high emission scenarios. From the historical to future eras, tropical cyclone genesis shifts northwards across seasons, with an increased likelihood of genesis adjacent to major coastlines. Proportional increases in genesis exceed 100% during the winter monsoon season and up to 50% during the summer monsoon season. Relative humidity and vertical wind shear become increasingly important influences on tropical cyclone genesis, particularly during the summer monsoon and autumn seasons. There are also increased likelihoods of tropical cyclones making their first landfall along the coastlines of the Philippines and Indonesia during the winter monsoon and spring seasons, and along mainland Southeast Asian coastlines during the summer monsoon and autumn seasons. These changes demonstrate the need for improved coastal resiliency and mitigation strategies in this highly populated part of the world.

Marine phytoplankton are crucial to oceanic ecosystems, yet trends in their activity, monitored through chlorophyll a, remain uncertain due to observational limitations. We generated an ocean chlorophyll a dataset (2001 to 2023) across low to mid-latitudes (45°N to 45°S) using multisource data and a deep learning approach. Our analysis suggests widespread decline in ocean greenness, with chlorophyll a concentrations decreasing at a rate of (-0.35 ± 0.10) × 10-3 milligrams per cubic meter per year (mg m-3 year-1). The decline is steeper in coastal regions [(-0.73 ± 0.22) × 10-3 mg m-3 year-1]. The frequency of high chlorophyll a concentration events in coastal waters has decreased at a relative rate of -1.78% per year. These trends are predominantly driven by rising sea surface temperatures, which enhance ocean stratification, suppress nutrient upwelling, and limit phytoplankton growth. These findings suggest a long-term decline in marine primary production and a reduced occurrence of phytoplankton blooms, potentially disrupting trophic interactions and oceanic carbon cycling.

In this article, we present a comprehensive review of decadal to multi-decadal climate variability during the Common Era (CE), focusing on their characteristics and mechanisms. We begin by summarizing recent advances in proxy reconstructions that reveal the paleo-evidence of decadal to multi-decadal climate variability during the CE. Decadal to multi-decadal variability has been observed in extensive sets of proxy records in the CE. Despite improvements in proxy records in the type, temporal resolution, and temporal coverage, there remains a lack of clear consistency in the preferred time scales and phases of the variability among different records. The agreements of decadal characteristics between proxy records and model simulations are higher during the periods with strong external forcings, but lower during periods of weak external forcing. We subsequently describe the recent modeling studies on the influences of external forcings and internal variability on decadal to multi-decadal climate variability with associated physical mechanisms, and some emerging research topics. Despite the improved understanding of climate variability and regional climate changes, especially over the eastern Asia summer monsoon region, several inconsistencies still exist, such as the amplitudes of responses to external forcings and relative contributions from external forcings and internal variability. The review ends with perspectives for future directions to reconcile discrepancies of decadal climate variability, such as applications of paleoclimate data assimilation and isotope-enabled transient climate modeling, and implications for projecting future decadal to multi-decadal climate changes and for improving the accuracy of decadal predictions.

The elderly face elevated mortality risk due to rising temperature. Previous assessments of temperature-related mortality, however, lack a comprehensive analysis of distinct impacts of temperature change across different timescales and characteristics. Using a longitudinal survey of 27,233 elderly Chinese citizens from 2005 to 2018, we establish connections between rising temperatures, temperature variability, and extreme heat with increased mortality risk, assessed through four annual metrics that combine temperature and humidity. The intensity and prolonged duration of extreme heat are found to have the greatest impact on mortality risk. Furthermore, by identifying heterogeneous impacts based on location, sex, age, obesity, income, and diet, we reveal the pathways through which temperature metrics are likely to influence mortality risk. Our study highlights the compound effects of rising temperatures for elderly populations, and it could be expanded to other countries and regions experiencing similar challenges due to an aging population experiencing warming conditions.