Atmospheric carbon dioxide, methane, and nitrous oxide all reached their highest recorded concentrations during the year. The globally averaged carbon dioxide concentration rose to 425.6 parts per million, with an uncertainty of approximately 0.1 parts per million. That level is about 53% higher than the estimated preindustrial concentration of 278 parts per million. Fossil fuel emissions also reached a new record, estimated at 10.3 petagrams of carbon per year, more than three times the annual level recorded during the 1960s. These gases trap outgoing infrared radiation, increasing the energy retained within the atmosphere, oceans, land, and ice.

Global temperatures remained exceptionally high even though the tropical Pacific did not experience a conventional El Niño event. The average temperature across Earth’s land and ocean surfaces ranked among the three warmest in records extending back to the mid-1800s. All five major global temperature datasets examined by the report agreed that the period from 2015 through 2025 contained the 11 warmest years ever measured. Europe experienced its warmest year on record, while Russia, China, the Republic of Korea, and Argentina each recorded their second-warmest year. The result makes 2025 the warmest year observed without El Niño conditions dominating the Pacific.

Sea surface temperatures were similarly unusual. Although cool ENSO conditions and weak La Niña patterns affected the equatorial Pacific during parts of the year, the global annual sea surface temperature was the third highest in the 172-year observational record. It stood approximately 0.38 degrees Celsius above the 1991–2020 average. Marine heat waves affected about 87% of the world’s ocean surface at least once during 2025, while only 26% experienced a marine cold spell. Such heat extremes can disrupt fisheries, damage coral reefs, alter marine food webs, and intensify evaporation, providing additional moisture and energy for some storms.

The ocean continued to act as Earth’s largest absorber of excess heat. Over roughly the past 50 years, the oceans have taken up nearly 90% of the additional energy trapped by greenhouse gases and other climate influences. Measurements extending from the surface to a depth of 2,000 meters showed that global ocean heat content reached another record in 2025. As seawater warms, it expands through thermal expansion, while melting glaciers and ice sheets add water to the ocean. Together, these processes pushed global mean sea level to a record for the 14th consecutive year, approximately 111.2 millimeters above the 1993 satellite-altimetry baseline.

The polar regions again showed some of the clearest signs of accelerated warming. The Arctic experienced its second-warmest year in a 126-year record, with surface air temperatures rising at roughly three times the global average rate. Increasing warmth and precipitation contributed to greater tundra vegetation, and Arctic greenness reached the third-highest level in the record. Yet sea ice continued to shrink. The Arctic’s maximum annual sea-ice extent was the lowest in 47 years of satellite observations, while the minimum was the 11th lowest. Ice older than four years, which is generally thicker and more resistant to melting, has nearly disappeared. In September 2025, only about 95,000 square kilometers of such ice remained, compared with approximately 1.5 million square kilometers during the 1980s.

Antarctica also recorded its warmest year since continuous records began in 1979. Surface melting exceeded average levels across most Antarctic ice shelves, and melting on the Antarctic Peninsula approached record values in early January. Sea ice surrounding the continent remained below average, continuing a nearly decade-long period of unusually low coverage. The annual maximum and minimum sea-ice extents ranked as the third and fourth lowest, respectively. Meanwhile, land-based glaciers worldwide lost ice for the 38th consecutive year. Their average loss exceeded one meter of water equivalent for the fourth year in a row, and approximately 41% of the total ice loss recorded since 1976 occurred during the last decade.

The atmosphere’s increasing heat and moisture were accompanied by an active tropical cyclone year. Ninety-seven named tropical cyclones formed across the Northern and Southern Hemisphere storm seasons, compared with a 1991–2020 average of 87. Five reached Category 5 intensity. Hurricane Melissa became one of the strongest Atlantic hurricanes ever recorded, reaching maximum winds of 190 miles per hour and a minimum central pressure of 892 hectopascals on October 28. It struck Jamaica as a Category 5 storm, causing severe destruction in the western part of the island, 95 reported deaths, and at least $12.2 billion in damage. In the Australian basin, 12 named storms formed during the 2024–25 season, the highest seasonal total since 2005–06. Tropical Cyclone Zelia reached Category 5 strength over the ocean before making landfall in Western Australia as a Category 4 storm.

The report’s findings do not describe isolated changes in a single part of the planet, but a connected shift across the climate system. Greenhouse gases are increasing the atmosphere’s heat-trapping capacity; the ocean is accumulating energy; sea level is rising; glaciers and polar ice are shrinking; and extreme heat and powerful storms are affecting ecosystems and communities. Because the State of the Climate is peer-reviewed and assembled from independent monitoring systems around the world, its value lies not only in individual records but in the consistency of the overall signal. The measurements show that Earth’s climate continued moving into unfamiliar territory in 2025, even during a year without a strong El Niño.

Subject of Research: Earth’s climate system, including greenhouse gases, global temperatures, oceans, sea level, polar regions, glaciers, and tropical cyclones.

Web References: State of the Climate report

References: State of the Climate in 2025, special supplement to the Bulletin of the American Meteorological Society, Vol. 107, No. 8, August 2026.

Image Credits: Figure 1.1 in the State of the Climate in 2025, special supplement to the Bulletin of the American Meteorological Society, Vol. 107, No. 8, August 2026.

Keywords: Climate change, global warming, greenhouse gases, carbon dioxide, ocean heat, sea-level rise, Arctic, Antarctica, glaciers, sea ice, marine heat waves, tropical cyclones, La Niña, climate monitoring.

Coastal wetlands, particularly those along the Louisiana coastline, serve as critical buffers against storm surges and harbor immense biodiversity while simultaneously playing a pivotal role in carbon sequestration. However, these ecosystems are under increasing threat from subsidence, sea-level rise, and anthropogenic land-use changes. Understanding the precise mechanisms that govern their ability to maintain elevation relative to rising sea levels is thus a matter of both scientific inquiry and environmental urgency.

The crux of Li and colleagues’ reply revolves around the concept of ecogeomorphic feedbacks—complex interactions where ecological processes influence geomorphology and vice versa, ultimately affecting sediment deposition patterns, vegetation productivity, and soil elevation. Their analysis actively engages with the findings of prior studies that emphasize the role of such feedbacks in microtidal settings, highlighting both consistencies and divergences in observational data and modeling approaches.

In detailing their argument, the authors underscore the multifactorial nature of wetland elevation changes. They argue that while ecogeomorphic feedbacks undeniably contribute to elevation gains through increased organic matter accumulation facilitated by vegetation, these factors are intricately linked with sediment supply, hydrodynamics, and regional geological subsidence. By integrating hydrological data with sediment transport models, the authors advocate for a more holistic framework to better predict wetland responses to environmental stressors.

Importantly, Li and colleagues challenge prior assumptions which may have overly isolated ecological contributions from the broader physical landscape context. Their reply presents new data analyses supporting the contention that sediment availability and microtidal hydrodynamics impose fundamental constraints on the magnitude and variability of ecogeomorphic feedbacks affecting elevation change. Such insights are pivotal in refining wetland management strategies that seek to optimize sediment delivery and vegetation restoration.

Furthermore, the paper elaborates on methodological advancements including remote sensing technologies combined with in situ measurements, which have facilitated more precise elevation tracking over decadal timescales. These innovations allow scientists to disentangle biogeomorphic signals from background processes such as subsidence linked to natural compaction and anthropogenic extraction activities. Consequently, the authors advocate for multi-scale monitoring networks to capture spatial heterogeneity inherent in wetland systems.

The reply also engages directly with critiques regarding the temporal scope and spatial resolution of previous studies, emphasizing the importance of long-term datasets to capture episodic events such as hurricanes and floods that can drastically alter sediment distribution and vegetation dynamics. Through rigorous statistical approaches, Li et al. demonstrate that episodic sediment deposition events can override gradual ecological feedbacks, complicating simplistic models of elevation gain.

Moreover, the authors bring attention to the implications of climate change-induced sea-level acceleration on microtidal wetlands, forecasting that without sustainable sediment replenishment, these systems may rapidly transition from net elevation gain to loss. This projection calls for integrated coastal zone management policies that reconcile natural feedback processes with engineered interventions like sediment diversions and marsh restoration.

In addition to field data, the authors critically examine process-based models simulating eco-geomorphic interactions, pointing out areas where model outputs diverge from empirical observations. They advocate for iterative model refinement incorporating feedback loops between plant productivity, organic matter decay, sediment trapping efficiency, and hydrodynamic forcing to faithfully represent system dynamics across scales.

The significance of this reply extends beyond regional geography; it contributes to the global understanding of wetland resilience mechanisms in microtidal environments. By challenging prevailing paradigms and urging nuanced interpretations, Li, Törnqvist, and Dangendorf stimulate new research trajectories that explore species-specific vegetation responses, sediment grain size effects, and microbial processes influencing soil building.

Ultimately, this dialogue resonates with wider ecological and environmental engineering fields by highlighting the need for interdisciplinary approaches melding geomorphology, ecology, hydrology, and climate science. Such integrative research is fundamental to crafting adaptive frameworks capable of sustaining coastal wetlands amid accelerating anthropogenic pressures and climate-related disturbances.

In conclusion, the reply by Li and colleagues exemplifies rigorous scientific engagement, presenting a nuanced critique and synthesis of ecological and geomorphic interactions governing wetland elevation. Their work calls for enhanced data integration, model sophistication, and management innovation to safeguard these vital ecosystems now and into the future. Through elucidating the delicate balances sustaining microtidal wetlands, this study reinforces the importance of maintaining sediment regimes and ecological functions in an era of unprecedented environmental change.

This research underscores the evolving narrative surrounding coastal resilience, affirming that ecology and geomorphology are inextricably linked components shaping the destiny of wetlands. As the scientific community continues to unravel these complex feedbacks, insights garnered from Louisiana’s microtidal wetlands will undoubtedly inform conservation and restoration practices worldwide, emphasizing a holistic perspective rooted in empirical rigor and systems thinking.

Subject of Research: Coastal wetland elevation dynamics and ecogeomorphic feedback mechanisms in microtidal environments.

Article Title: REPLY TO “Ecogeomorphic feedbacks influence elevation change across microtidal wetland settings of coastal Louisiana”.

Article References:
Li, G., Törnqvist, T.E. & Dangendorf, S. REPLY TO “Ecogeomorphic feedbacks influence elevation change across microtidal wetland settings of coastal Louisiana”. Nat Commun 17, 1502 (2026). https://doi.org/10.1038/s41467-026-69092-x

Image Credits: AI Generated

DOI: https://doi.org/10.1038/s41467-026-69092-x

Groundwater beneath the Earth’s surface is an indispensable resource, accounting for nearly half of the global domestic water supply. However, a significant proportion of this groundwater is classified as fossil water — ancient water that infiltrated subsurface reservoirs more than 11,700 years ago, before the onset of the Holocene epoch. These waters have remained isolated for such vast timescales that they are effectively non-renewable. Their longevity and vulnerability to contamination and saline intrusion present serious challenges for sustainable water management, especially in the face of accelerating environmental change.

The study, led by researchers at Stockholm University, takes on this challenge by probing how fossil groundwater beneath formerly glaciated regions has responded to drastic climatic events, including glacial retreats and associated sea level rises. Wei-Li Hong, a principal investigator in the Geological Sciences Department, highlights the importance of regions once cloaked by massive ice sheets, positing that the movement and chemistry of deep groundwater in these zones can offer critical clues about past environmental shifts.

One critical obstacle in understanding these processes has been the inaccessibility of subsurface environments beneath thick ice masses. Traditionally, drilling beneath glaciers to sample groundwater directly has been technically daunting and costly. To circumvent this barrier, the research team innovatively targeted submarine groundwater discharge, where fresh groundwater flows into the ocean. By examining waters emerging through the seabed offshore from northern Norway, they accessed a natural outflow reflecting underground hydrological processes beneath the former Fennoscandian ice sheet.

Sampling at approximately 760 meters below sea level along the Lofoten-Vesterålen margin, the researchers collected fluid samples uniquely freshened compared to typical seawater. This discovery is potent evidence that glacial meltwater had infiltrated the subsurface during the ice sheet’s maximum extent and subsequently discharged into the marine environment. The presence of this freshened groundwater suggests a previously underappreciated connection between past ice dynamics and subsurface hydrology.

Central to the study’s methodology was the use of radiocarbon dating of dissolved inorganic carbon in the submarine groundwater. Radiocarbon content serves as a robust chronological marker, revealing the last time the groundwater was in contact with the atmosphere prior to its subsurface isolation. PhD researcher Sophie ten Hietbrink explains that this technique enabled the team to constrain precisely when the groundwater flowed beneath the glacier and when seawater eventually replaced it during glacial retreat and marine transgression phases.

The temporal data indicate that during the height of glaciation—when ice thickness reached roughly one kilometer—meltwaters actively penetrated and replenished underground aquifers. However, following the collapse of the Fennoscandian ice sheet and the progressive advance of rising seas, this ancient fresh groundwater was slowly displaced by invading seawater. This seawater encroachment curtailed the discharge of fresh glacial meltwater into the ocean and altered the geochemical composition of subsurface fluids.

Notably, this infiltration of seawater into fossil groundwater systems poses significant implications for the longevity and quality of subterranean freshwater reserves beneath continental shelves. The study’s results suggest that without continual supply from glacial melt, these deep reservoirs become increasingly vulnerable to saline contamination on timescales of just a few thousand years, highlighting their fragility in a changing climate.

From a broader geoscientific perspective, the findings challenge previous conceptual models about the stability and dynamics of submarine groundwater systems during deglaciation. The interplay between ice sheet retreat, sea level rise, and groundwater flow revealed here underscores complex feedback mechanisms that may influence glacier mass balance by modulating basal hydrology and sediment stability beneath ice masses.

Furthermore, the research sheds light on potential biogeochemical impacts in coastal marine environments. As groundwater discharges into the ocean, it carries with it nutrients and carbon compounds that can affect local ecosystems and carbon cycling. Understanding the timing and chemistry of these discharges is therefore essential for predicting how coastal waters might respond to ongoing environmental perturbations.

Importantly, this study opens new avenues for future investigations into submarine groundwater flow in other glaciated regions, including Greenland, Antarctica, and the Arctic archipelago of Svalbard. Given the current trends of accelerated ice sheet melting in these areas due to anthropogenic warming, unraveling groundwater-ice sheet interactions will be critical for improving predictive models of sea level rise and freshwater input to oceans.

Wei-Li Hong emphasizes the urgency of continuing this line of work, noting that monitoring submarine groundwater systems could provide invaluable insights into the mechanisms driving glacier retreat and the subsequent fate of ancient freshwater reservoirs. As melting glaciers liberate more freshwater into the marine environment, understanding these subsurface processes may also inform water resource management and conservation strategies in coastal regions.

In summary, this innovative study represents a milestone in paleo-hydrogeology, revealing that fossil groundwater beneath the ocean floor is not a static relic but has been dynamically shaped by glacial-interglacial cycles. By combining cutting-edge radiocarbon analytical techniques with detailed marine sampling, the research unites hydrology, glaciology, and marine science to offer a more nuanced perspective on Earth’s changing climate system and its hidden freshwater archives.

Subject of Research:
Not applicable

Article Title:
Deglaciation drove seawater infiltration and slowed submarine groundwater discharge

News Publication Date:
6-Aug-2025

Web References:
http://dx.doi.org/10.1038/s41561-025-01750-z

References:
Hong, W.-L., ten Hietbrink, S., Chen, N.-C., et al. (2025). Deglaciation drove seawater infiltration and slowed submarine groundwater discharge. Nature Geoscience. DOI: 10.1038/s41561-025-01750-z

Image Credits:
Credit: Sophie ten Hietbrink

Keywords:
Ancient groundwater, fossil water, submarine groundwater discharge, radiocarbon dating, deglaciation, Fennoscandian ice sheet, sea level rise, glacial meltwater, ocean floor hydrology, climate change, marine geoscience, ice sheet stability

Traditional assessments rely heavily on tide gauge measurements, which record water levels in coastal waters and inform two widely accepted flooding thresholds: the National Oceanic and Atmospheric Administration (NOAA) High Tide Flooding (HTF) threshold and the National Weather Service’s (NWS) minor flood threshold. These thresholds have dictated our comprehension of flood frequency and duration, guiding public policy and infrastructure planning. Yet this reliance on marine-level data fails to capture the complex, localized dynamics of flooding on the land itself, especially as sea-level rise accelerates and brings unprecedented challenges to coastal regions.

The study’s authors, including Miyuki Hino and Katherine Anarde, bring a multidisciplinary approach to this issue, merging city and regional planning with coastal engineering. They emphasize that tide gauges effectively measure water levels in open water but do not adequately reflect the sustained presence of water permeating land surfaces, which directly affects communities. Floodwaters that inundate streets and neighborhoods can persist for extended periods, but these durations often remain invisible to gauge-based thresholds. This discrepancy necessitates a radical shift towards land-focused flood monitoring systems.

To address these methodological gaps, the research team developed and deployed a network of specialized land-based sensors across three vulnerable North Carolina coastal communities: Beaufort, Carolina Beach, and Sea Level. Unlike tide gauges positioned offshore, these sensors were strategically situated on roadways to detect actual flooding impacting daily life and infrastructure. Over the course of one year, the sensors recorded flood events with remarkable fidelity, documenting the real-world impact on communities and revealing a level of flooding previously unreported.

The contrasting results between tide gauge data and sensor readings were striking. In Sea Level, for instance, the sensors detected flooding on 128 days during the study period, a figure that dramatically surpassed the 31 days indicated by the NWS minor flood threshold and the mere 9 days recognized by the NOAA HTF standard. When excluding extreme storm events like hurricanes, these discrepancies remained profound. Such findings underscore the limitations of current monitoring frameworks that underestimate flood frequency, potentially leaving communities unprepared for the growing reality of recurrent flooding.

Furthermore, the study elucidates how tide gauge-based thresholds sometimes overestimate flooding, exemplified by Carolina Beach, where sensor data showed 65 flood days, but NWS thresholds suggested 120 days. This overestimation points to the complexity of accurately correlating water levels offshore with terrestrial flooding occurrences. It sheds light on the nuanced spatial variability of flooding influenced by local topography, drainage infrastructure, and land use, which cannot be adequately resolved through marine measurements alone.

Beyond frequency, the duration of flooding is a critical dimension overlooked by traditional tide gauge analysis. Researchers observed that water levels on the land take longer to recede, prolonging flood impact on residents and infrastructure. Marine tide measurements often miss this delayed drainage process, leading to underreported flood durations. Accurately capturing how long inundation lasts is vital for emergency response, urban planning, and designing resilient infrastructure that can withstand persistent water exposure.

The implications of these findings are profound for policy, urban design, and climate adaptation strategies. Coastal communities around the world are confronting the dual pressures of sea-level rise and more frequent, chronic flooding events. Reliance on outdated measurement approaches risks misinforming preparedness and mitigation efforts, potentially exacerbating vulnerabilities. Incorporating land-based sensor data promises a more accurate picture of flood risk, enabling targeted investment in flood defenses, infrastructure retrofitting, and community resilience.

The study’s authors are actively collaborating with local governments and community organizations to translate these technological and scientific advancements into actionable strategies. Recognizing that each coastal community faces unique geographic and social circumstances, the team advocates for customized interventions informed by precise, locally gathered data. This approach departs from one-size-fits-all solutions, emphasizing tailored responses that address specific challenges and priorities of affected populations.

Technical innovation in flood monitoring extends beyond sensor deployment. Researchers integrate sensor data with hydrodynamic modeling, geographic information systems (GIS), and real-time analytics to map flood pathways, predict future flooding scenarios, and evaluate mitigation measures. This fusion of observational and computational techniques represents a frontier in environmental engineering, catalyzing smarter, data-driven responses to climate-induced challenges.

This research is published in the open-access journal Communications Earth & Environment, ensuring that its insights are widely accessible to scientists, policymakers, and the public. By leveraging state-of-the-art land-based sensing technology, the study pioneers a new paradigm in coastal flood detection, emphasizing the importance of ground truth data that reflects the lived experience of residents rather than purely marine observations. Its findings serve as a clarion call for reevaluating flood monitoring standards in an era of accelerating sea-level rise.

The funding sources for this work span federal agencies, environmental programs, and academic institutions, reflecting broad recognition of its significance. Support from the U.S. Department of Homeland Security, NOAA, NASA, the National Science Foundation, and regional stakeholder partnerships underscores the interdisciplinary and applied nature of the research. Together, these efforts aspire to safeguard coastal communities through enhanced understanding and management of flood risks.

As climate models project continued sea-level rise and increased frequency of high-tide flooding, the urgency of refining our measurement tools cannot be overstated. This study’s demonstration of chronic flooding outside of extreme weather events shifts the narrative around coastal risk, highlighting everyday flood hazards that degrade quality of life and impose economic burdens. The integration of land-based sensors presents a pivotal advancement in monitoring, equipping communities with the knowledge needed to build resilience in the face of rising waters.

In conclusion, this pioneering research challenges entrenched methodologies in coastal flood assessment, underscoring the necessity of land-based measurements alongside traditional marine data. It paints a more comprehensive portrait of flooding events, revealing heightened frequency and duration that bear direct consequences for vulnerable populations. The study’s innovative approach fosters a deeper understanding of coastal flooding dynamics, setting the stage for improved adaptation strategies and more resilient coastal futures.

Subject of Research: Not applicable

Article Title: Land-based Sensors Reveal High Frequency of Coastal Flooding

News Publication Date: 2-Jun-2025

Image Credits: Sunny Day Flooding Project

Keywords: coastal flooding, land-based sensors, tide gauge data, sea-level rise, flood frequency, flood duration, flooding monitoring, coastal resilience, environmental engineering, climate adaptation, urban planning, flood mitigation