We model Cenozoic temperature and ice volume changes using the Pacific benthic δ 18 O record and a global compilation of foraminiferal Mg/Ca data. In our model, the proportion of δ 18 O benthic variation reflecting temperature change over time is parameterized, and a benthic foraminiferal paleotemperature equation is used to estimate δ 18 O sw . Barystatic sea level (BSL) is derived using an ice-sheet model that defines temporal variability in the ratio of δ 18 O sw to BSL change. We calibrate parameters to align model output BSL and temperature variations with independent sea-level estimates and Mg/Ca-derived temperatures. Our approach is conceptually similar to previous efforts to decompose δ 18 O benthic using Mg/Ca data as temperature constraint, but differs through our application of the ice-sheet model and a Bayesian inversion framework. Our results indicate a modestly sized Antarctic ice sheet is present through most of the Paleocene and Early Eocene. Large Antarctic and modest Northern Hemisphere ice sheets (NHIS) developed after the Eocene-Oligocene transition, though the NHIS melted during most interglacial periods and through the Miocene Climate Optimum. Milankovitch forcing produced 100 kyr BSL variability that increased from ~5 m in the Paleocene to 30–40 m through the Oligocene and Early to early Middle Miocene, before diminishing to 20–30 m in the late Middle to Late Miocene. The amplitude rose again to ~40 m in the Early Pliocene and has increased to 80–100 m 100 kyr over the past Myr. Constructive interference of precession, obliquity, and eccentricity produces large variations in deep sea paleotemperature and BSL, especially at a ~100 kyr periodicity.

Abstract Due to sea‐level rise, densely populated coastal areas are facing increasing flood risk during coastal storms. Much of the US East Coast experiences extratropical cyclones (ETCs) more frequently than tropical cyclones (TCs), yet many studies on extreme flood risk focus primarily on TCs or exclude ETCs altogether. ETCs occur primarily during November to April (henceforth, the cool season), while TCs occur primarily during May to October (henceforth, the warm season). This study performs a quasi‐nonstationary skew surge joint probability (qn‐SSJPM) analysis of storm tide exceedance distributions for cool and warm seasons from 23 tide gauges along the US East Coast to assess seasonal contributions to extreme sea levels. From Boston, MA northward, cool‐season extreme storm tides predominate, while south of Wilmington, NC, warm‐season storm tides predominate. Using an illustrative property damage curve, we show that, for New York City, cool‐ and warm‐season storms cause comparable amounts of average annual property damage. These findings highlight the importance of treating cool‐ and warm‐season storms as statistically separate to improve flood risk analysis.

How fast future sea level rises will depend on the Antarctic Ice Sheet (AIS) response to warming. AIS projections are shaped by the assumption that sea-level peaks during past interglacials occurred after the North American ice sheet complex (NAIS) disappeared. We synthesize evidence from paleoceanography and allied disciplines to argue that NAIS persisted into some of the warmest interglacials of the last million years. We show that overlooking NAIS persistence may lead to underestimation of AIS sensitivity to warming, and propose that this paradigm shift opens research avenues that can increase confidence in the accuracy of climate and sea-level projections.

Abstract For more than 40 years, scientists have projected future sea‐level change. Documenting how sea‐level projections have evolved is vital for tracking progress, uncertainties, and future research needs. Here, we update and analyze a database of global‐mean sea level (GMSL) projections dating from 1982 to 2025, identifying five key findings. First, GMSL projection generation has been concentrated in a small number of developed countries, with 95% of projections produced in the United States, United Kingdom, European Union, or Australia. Second, while GMSL projections for 2050 and 2100 have been published regularly since the early 1980s, only 30 of 103 studies have produced projections extending beyond 2100; all but one of these 30 studies postdates 2010. Third, among studies providing multiple estimates, the range of highest GMSL projections for 2100 has broadened since 2007, reaching 0.6–2.0 m across publications since the Intergovernmental Panel on Climate Change (IPCC) Sixth Assessment Report (AR6). Fourth, GMSL projections from the IPCC have historically been conservative compared to projections from individual studies. Prior to AR6, ∼66% of 2100 projections at the upper end of uncertainty intervals from individual studies exceeded the corresponding upper projections from IPCC reports. However, the inclusion of “low‐confidence” GMSL projections in AR6 to assess higher amounts of GMSL change of poorly known likelihood reduces this problem: the 83rd percentile of these low‐confidence projections is exceeded by <25% of upper estimates from individual studies. Finally, analyses suggest that the arrival time of key GMSL milestones are often similar for projections spanning multiple eras and using various methodologies.

This paper produces the first estimates of local damages from climate change, reflecting heterogeneous exposure and responses to climate for ∼25,000 globally comprehensive regions. Global damages from a marginal ton of CO 2 emissions (i.e., the social cost of carbon) are $336 (2025 USD), with just 5% occurring in OECD countries that account for half of historical emissions. Restricting to country-level analysis obscures half the variation in local damages. Despite large benefits from adaptation and modest average impacts, 7% of world population experiences annually recurring Great Recession level damages by 2100 under business-as-usual warming. These findings illustrate climate change's marked inequality.

The rate and impacts of sea level rise vary considerably around the world, but the contribution of human-caused climate change to increases in local and regional flood risks has not yet been systematically explored. Because such information is critical to local decision making, legal proceedings, and loss and damage determinations, we quantify human-caused climate change's contributions to sea level rise at worldwide locations using budget-based and semiempirical model methods. Results show that human-caused sea level rise is quantifiable at 97% of 519 tide gauge sites and is responsible for 58% (44 to 65%) of the observed daily extreme water level exceedances over 2000-2018. On average, human-caused sea level rise has caused a near-tripling in the number of days with attributable exceedances since the 1970s.

Proxy relative sea level (RSL) reconstructions offer context for historical observations and future projections. Unlike many sites in the equatorial Pacific Ocean where Late Holocene RSL fell from a high stand, the subsiding volcanic islands of Pohnpei and Kosrae in Micronesia experienced continuous RSL rise, allowing mangrove sediment accumulation. Through sedimentological, geochemical, and palynological techniques alongside radiocarbon dating, we reconstruct RSL over the past similar to 3000 years. On Pohnpei, RSL rose 3.6 +/- 0.17 m since 1270 BCE and on Kosrae RSL rose 1.9 +/- 0.33 m since 310 BCE. Our findings indicate subsidence rates of 1.3 mm/y for Pohnpei and 1.1 mm/y for Kosrae, consistent with contemporary rates, but greater than expected based on current understanding of the lifespan of ocean islands. These new estimates do not significantly alter existing twenty-first-century RSL projections for Pohnpei but given the similarity in predicted and reconstructed RSL histories between Pohnpei and Kosrae, we anticipate that for planning purposes, future RSL rise at Kosrae will resemble that of Pohnpei. Our work integrates these reconstructions into an updated global mean sea-level curve, emphasizing the value of Late Holocene proxy data from under-represented regions.

Future sea-level rise poses substantial risks to the densely populated and economically critical coastlines of East Asia, yet coastal projections from global climate models (GCMs) remain uncertain because shallow-shelf ocean dynamics governing sterodynamic sea level (SDSL) are poorly resolved. Here we combine dynamically downscaled SDSL with other sea-level components to produce improved projections under SSP2-4.5. By 2100, regional-mean relative sea level across East Asia shelf regions rises by 61 (40–89) cm, with SDSL as the largest component (39%) and up to 18% higher than GCM-based estimates. Incorporating improved SDSL and local subsidence, we assess sea-level projections and socioeconomic risks for representative metropolitan centers. The 100-year extreme sea level rises by 23–69% by 2100, driving increases in inundated land area, exposed population and physical capital up to 58%, 238%, and 148%, respectively. These results highlight urgent coastal risks and provide a credible basis for adaptation planning across East Asia.

Abstract. Simplified sea level modelling approaches calibrated against reference data, also referred to as sea level emulators, can explore future sea level rise and associated uncertainties with low computational cost. Here, we introduce the Sea Level Emulator Intercomparison Project (SLEIP) to assess available sea level emulators and identify future research needs. The SLEIP protocol has a multi-century focus with 2300 as the end year to explore more of the impact-relevant time horizon and also investigate sea level responses under temperature overshoot. SLEIP covers a total of 13 sea level datasets from the participating emulators BRICK, FACTS (7 individual emulator workflows), FRISIA, MAGICC, MP25, ProFSea and SURFER. The sea level components of participating emulators range from statistical models fitted to projections or observational data to physical parametrizations, to coarse spatio-temporal physical models. They also differ in whether and, if yes, how they account for low-confidence ice-sheet processes. To remove the influence of different climate forcings on the sea level responses, we run the participating emulators with both their native climate forcings and a common forcing from the MAGICC climate model. We provide an analysis of the emulator output for the 2300 projection horizon as well as the historical period. SLEIP fills a gap in the IPCC AR6 sea level assessment by providing 2300 projections for three additional policy-relevant pathways. In the MAGICC-forced configuration, the 2300 probability boxes (p-boxes: mean of medians, lowest 17th to highest 83rd percentile) for total global mean sea level rise relative to 1995–2014 are 0.93 m (0.30–3.15 m) under the 1.5 °C-consistent SSP1-1.9, 1.36 m (0.56–10.85 m) under the strong overshoot scenario SSP5-3.4-OS, and 2.08 m (0.97–11.00 m) under SSP2-4.5, which has been used as a proxy for current climate policies. Native-forced projections generally agree closely with the MAGICC-forced results, indicating that structural differences between sea level models dominate over climate forcing, with the Antarctic ice sheet as the largest source of uncertainty. The relative consistency of thermal expansion and glacier contributions largely reflects shared parametrizations and common calibration datasets rather than independent agreement. Under SSP5-3.4-OS, an overshoot sea level rise penalty of roughly 0.1 to 0.3 m persists by 2300 compared to SSP1-2.6, even after global mean surface air temperature has returned to the SSP1-2.6 level by 2150. This first phase of SLEIP provides a lay of the land of current sea level emulation. Future phases will build on this with ScenarioMIP-CMIP7 scenarios, targeted sensitivity experiments, and a potential extension toward regionally resolved projections.

Decisions about how to respond to coastal flood hazards often involve disagreements over resource allocations. In the United States, large intergovernmental fiscal transfers have enabled rebuilding in areas that experience severe repetitive losses. This case study focuses on Ortley Beach, a barrier island neighborhood in Toms River, New Jersey, to examine the process of rebuilding after Superstorm Sandy in 2012 and competing visions for the future. A decade later, we conducted 32 key-informant interviews-including residents and local, state, and federal officials-to examine how values, worldviews, and beliefs shape preferences for coastal risk reduction strategies. A central debate was whether public resources should support staying or leaving the island. Key concerns included the economic impacts of strategies on household and public finances, the effectiveness of strategies to mitigate future flood damages, and fairness in the distribution of costs and responsibilities. Conflicts emerged in how stakeholders framed their preferences. Local officials tended to hold more individualistic-hierarchical worldviews, weaker beliefs in climate science, and favored actions to protect high-value properties to preserve the tax base while externalizing costs. In contrast, some residents and most state and federal officials held more community-egalitarian worldviews, stronger beliefs in climate science, and preferences for long-term adaptation strategies to reduce risk, including property buyouts. Responding to the primary concern about economic impacts, we recommend enhancing individual and local financial resilience to climate and political shocks by diversifying municipal revenue streams, encouraging proactive risk-based planning, exploring innovative insurance models, and better accounting for the long-term costs of rebuilding.

Our ability to characterize and quantify the complex uncertainties surrounding future sea-level changes is crucial for coastal risk assessments and adaptation strategies. This study focuses on the role of steric and dynamic changes (i.e., sterodynamics) in sea level projections, particularly regarding their contribution to the uncertainty of global and regional sea level changes in relation to other components such as ice sheet dynamics. A probabilistic framework is used to estimate probability distributions of sea-level change for each component. Through variance decomposition, the total uncertainty in sea-level change is dissected into its constituent sources. Subsequently, the relative contribution of sterodynamics uncertainty is quantified across various regions, time frames, emission scenarios, and projection methodologies utilized to estimate future sea-level distributions. The contribution of sterodynamics to overall uncertainty reduces over time as the contribution from ice sheets becomes more pronounced. The spatiotemporal pattern of sterodynamic significance is not strongly dependent on future greenhouse gas emissions, yet its overall role is highly dependent on the representation (e.g., emulation) of ice sheets. When high-end, low-probability estimates of future Antarctic ice sheet contributions are excluded, sterodynamics remain a dominant source of regional sea-level uncertainty at the end of this century, particularly along the US East Coast and European coast. These regions are also identified as hotspots for future sea-level rise, indicating that sterodynamic processes will play a significant role in assessing coastal vulnerabilities there. This study suggests that ocean model development can most effectively reduce the overall uncertainty in future sea-level projections by focusing on these areas.

Harnessing scientific research to address societal challenges requires careful alignment of expertise, resources, and research questions with real‐world needs, timelines, and constraints. In the case of place‐based research, studies can avoid misalignment when grounded in the realities of specific locations and conducted in collaboration with knowledgeable local partners. But literature on best practices for such research is underdeveloped on how to identify appropriate locations and partners. In practice, these research‐design choices are sometimes made based on convenience or prior experience—a strategy labeled opportunism. Here we examine a deliberative and exploratory approach in contrast to default opportunism. We introduce a general framework for scoping place‐based opportunities for research and engagement. We apply the framework to identify climate‐adaptation planning decisions, rooted in specific communities, around which to organize research and engagement in a large project addressing coastal climate risks in the Northeast US. The framework asks project personnel to negotiate explicit project goals, identify corresponding evaluation criteria, and assess opportunities against criteria within an iterative cycle of listening to needs, assessing options, prioritizing actions, and refining goals. In the application, we elicit a broad range of objectives from project personnel. We find that a structured process offers opportunities to collaboratively operationalize notions of equity and justice. We find some objectives in tension—including equity objectives—indicating trade‐offs that other projects may also need to navigate. We reflect on challenges encountered in the application and on near‐term costs and benefits of the exploratory process.

We estimate ice-volume driven (barystatic; BSL) sea-level changes for the Cenozoic using new Mg/Ca data from 58 to 48 Ma and a revised analysis of Mg/Ca trends over the past 66 Myr. We combine records of BSL, temperature-driven sea level, and long-term ocean basin volume variations to derive a new global mean geocentric sea level (GMGSL; “eustatic”) estimate. Bayesian analysis with Gaussian process priors shows that our BSL estimate shares a component that covaries on the Myr scale with “backstripped” relative sea-level (RSL) estimates (accounting for compaction, loading, and thermal subsidence) from the US Mid-Atlantic Coastal Plain, validating our method and estimates with errors of ±10 m. Peak warmth, elevated GMGSL and BSL, high CO2, and ice-free conditions occurred at times in the Paleocene to Eocene (ca. 64, 57.5, 35 Ma) and in much of the Early Eocene (55–48 Ma). However, our new results show that the Early Eocene was punctuated at specific times by several Myr-scale sea level lowerings (∼20–40 m) that require growth and decay of significant continental ice sheets even in the supposedly “ice-free” world. Continental-scale ice sheets waxed and waned beginning ca. 34 Ma (>50 m BSL changes), with near complete collapse during the Miocene Climate Optimum (17–14.8 Ma). Both the BSL and RSL estimates have markedly higher Oligocene to Early Miocene Myr-scale amplitudes (20–60 m) than recently published δ18O-based estimates (<20 m) and much lower estimates than those of Exxon Production Research (>100 m), leading us to reject those estimates. The US Mid-Atlantic margin RSL was dominated by GMGSL but was overprinted by changes in mantle dynamic topography on the several Myr scale, showing approximately 50 m higher Eocene estimates and regionally propagating Miocene RSL changes.

Dynamic adaptation policy pathways provide a roadmap for coastal communities to establish a suite of sea level rise adaptation responses based on observation-driven signals of increasing risk. This adaptation approach relies heavily on iterative assessment of sea level rise observations and model projections. Remote sensing capabilities from satellites offer an opportunity to assess a consistent set of observational data indicators, around which adaptation pathways can be built. The large-scale nature and broad coverage of satellite observations provide the benefit of consistent monitoring capabilities across the globe, for regions with differing needs, resources, and monitoring capacities. In this study, we identify four categories of data indicators that can be monitored with satellites to support decision making in adaptation pathways: sea level rise, individual processes contributing to sea level rise, impacts of sea level rise, and impacts on implemented adaptation strategies. We review these categories in relation to existing adaptation pathway signposts and the available satellite data. As we highlight the opportunities for satellite-based contributions to sea level adaptation pathways, we also outline potential limitations, opportunities to overcome these limitations, and future steps that can be taken to integrate satellite observations into adaptation pathways.

Global mean sea-level (GMSL) change can provide insight on how ice sheets, glaciers, and oceans respond to warming[1;2]. The Holocene (11.7 ka to present) marks a time when temperatures may have exceeded early industrial (1850 CE) values[3]. Evidence from Greenland[4] and Antarctica[5;6] indicates that both ice sheets retreated inland of their present-day extents during the Holocene, yet previous GMSL reconstructions suggest that Holocene GMSL never surpassed early industrial levels7–9. We combine relative sea-level observations with glacial isostatic adjustment predictions from an ice-sheet model ensemble and new estimates of postglacial thermosteric sea-level and mountain glacier evolution to estimate Holocene GMSL and ice volume. We show it is likely (probability P =0.79) that GMSL exceeded early industrial levels in the mid-Holocene (8-4 ka) by up to 1.5 m and that the Antarctic Ice Sheet was likely (P =0.66) smaller than present in the last 6000 years. We demonstrate that Antarctic retreat lags Antarctic temperature by 250 years, underscoring future Antarctic vulnerability to present warming. Comparing our reconstruction to future projections indicates that GMSL rise in the next 125 years will very likely (P >0.9) be the fastest in the last 5000 years, and that by 2080 GMSL will more likely than not be the highest in 115,000 years.

Rising sea levels in the 21st century threaten coastal communities with inundation, yet projecting the relative and global mean sea level response to climate warming is complex. Lack of contemporary analogues for future climate dynamics has turned attention to periods in the geologic past that can illuminate how Earth’s climate system reacts to temperature forcing. Recent evidence suggests the Antarctic and Greenland ice sheets may have retreated inland of their present-day extents during the mid-late Holocene (~8-3 ka), then readvanced until the pre-industrial. These findings have highlighted the utility of the mid-Holocene—when summer temperatures in the northern hemisphere may have neared 4 degrees hotter than preindustrial levels—as a partial analogue for future warming. Here we present a new probabilistic estimate of mid-Holocene global mean sea level (GMSL). We construct an ensemble of global ice sheet reconstructions for the last 80 kyr that spans a range of possible mid-Holocene GMSL scenarios. We predict relative sea level from each model accounting for glacial isostatic adjustment and using a range of solid earth structures. We then compare these predictions to 10,733 postglacial sea-level indicators and weigh the GMSL curves from each ice model using data-model fits. The constraints placed on mid-Holocene global mean sea level clarify climate dynamics during this critical interval in Earth’s recent history, and enable new estimates of post-glacial Antarctic ice volume and the likelihood of mid-Holocene West Antarctic ice sheet readvance.

Abstract The artificial impoundment of water behind dams causes global mean sea level (GMSL) to fall as reservoirs fill but also generates a local rise in sea level due to the increased mass in the reservoir and the crustal deformation this mass induces. To estimate spatiotemporal fluctuations in sea level due to water impoundment, we use a historical data set that includes 6,329 reservoirs completed between 1900 and 2011, as well as projections of 3,565 reservoirs that are expected to be completed by 2040. The GMSL change associated with the historical data (−0.2 mm yr−1 from 1900–2011) is consistent with previous studies, but the temporal and spatial resolution allows for local studies that were not previously possible, revealing that some locations experience a sea level rise of as much as 40 mm over less than a decade. Future construction of reservoirs through ~2040 is projected to cause a GMSL fall whose rate is comparable to that of the last century (−0.3 mm yr−1) but with a geographic distribution that will be distinct from the last century, including a rise in sea level in more coastal areas. The analysis of expected construction shows that significant impoundment near coastal communities in the coming decades could enhance the flooding risk already heightened by global sea level rise.