Benjamin Dillon Hamlington

The deep ocean (>2,000 m) comprises ∼50% of the total ocean volume and is crucial in Earth's climate system, yet its warming remains uncertain owing to limited observations. We revisit the recently reported non‐closure of the global mean sea‐level (GMSL) budget and show that, despite instrumental corrections, the budget residual has increased since the mid‐2010s. Furthermore, the contribution of ocean heat uptake above 2,000 m to Earth's energy imbalance (EEI) has declined from approximately 80% to nearly 50% after the mid‐2010s, leaving a larger fraction of the EEI to be accounted for by deep ocean and other components of the climate system. When the GMSL budget residual was converted into the deep‐ocean heat uptake, the total heat uptake is consistent with the corresponding EEI estimates within uncertainty. These results demonstrate quantitative consistency between the GMSL and EEI budget residuals and suggest that deep‐ocean heat uptake have increased since the mid‐2010s.

Large submarine earthquakes introduce significant distortions into the ocean bottom pressure (OBP) data from the Gravity Recovery and Climate Experiment (GRACE) and its follow‐on mission (GRACE‐FO), leading to non‐closure of regional sea‐level budgets in seismically active oceans. In this study, we show that earthquake‐induced seafloor deformations can be effectively isolated using an iterative Empirical Orthogonal Function method that accounts for both co‐seismic and post‐seismic effects. The resulting seismic biases are systematic, driven by ongoing tectonic drift, and can (a) exceed total steric contributions to sea‐level change in some regions and (b) surpass Glacial Isostatic Adjustment (GIA) contributions in the global mean. These findings indicate that seismic deformation represents a non‐negligible component for separating natural and human‐driven contributions in climate assessments. Applying the seismic corrections to the OBP fields restores regional sea‐level budget closure and improves the physical consistency of oceanographic and climate analyses.

Local to global scale projections of future coastal landscape change are essential to improve land and resource management decisions that aim to prepare for and reduce risk exposure to impending coastal hazards. However, the availability of actionable knowledge is often limited due to the complexity of drivers of change, their consequences, and uncertainties that span disciplines. Varying spatial and temporal scales of physical processes that occur on landscapes with differing levels of coastal development and modification complicate decision‐making. This paper reviews advances in observational approaches, modeling, and quantification of uncertainty to support the next generation of coastal change projections. We also highlight transdisciplinary opportunities for making this information more accessible and useful to support decision‐making in the coastal zone. This includes consideration of different levels of user engagement to address specific needs, as well as resources and mechanisms that can support knowledge transfer broadly. A central recommendation is the development of a coordinated framework to support research integration including three components: accounting for relevant drivers, processes, and feedbacks; working with users to identify their information needs; and generating meaningful projections and uncertainty. Actions that would support such frameworks include the evaluation of models through coordinated research approaches and multi‐model comparisons; ongoing investments in observations and data‐driven approaches necessary to understand this complex environment; expansion of modeling capabilities using novel techniques; prioritization of co‐development efforts between researchers and users; and continued training and support for transdisciplinary research.

With an acceleration of global sea‐level rise during the satellite altimetry era (since 1993) firmly established, it is now appropriate to examine sea‐level projections made around the onset of this time period. Here we show that the mid‐range projection from the Second Assessment Report of the IPCC (1995/1996) was strikingly close to what transpired over the next 30 years, with the magnitude of sea‐level rise underestimated by only ∼1 cm. Projections of contributions from individual components were more variable, with a notable underestimation of dynamic mass loss from ice sheets. Nevertheless—and in view of the comparatively limited process understanding, modeling capabilities, and computational resources available three decades ago—these early attempts should inspire confidence in presently available global sea‐level projections. Such multidecadal evaluations of past climate projections, as presented here for sea‐level change, offer useful tests of past climate forecasts, and highlight the essential importance of continued climate monitoring.

Since 1993, satellite altimeters have been mapping sea level changes globally, revealing both the global mean rate and detailed patterns of regional variations. The global mean rate is well studied, closely linked to global energy and water cycles, while regional patterns are influenced by a complex mix of internal climate dynamics and external factors like greenhouse gases and aerosols. Yet, a synthesis of these regional patterns using a comprehensive diagnostic approach has been lacking. Our research addresses this gap by integrating oceanic and atmospheric observations with large ensembles of state‐of‐the‐art global climate models. This approach sheds new light upon the mechanisms behind basin‐scale sea level patterns worldwide. A key finding is the dominant influence of wind forcing, particularly Ekman and Sverdrup dynamics, in shaping sea level changes from the tropics to higher latitudes. We find that the pattern of sea level rise since 1993 is primarily driven by wind‐induced changes in ocean circulation, which can affect sea surface height through ocean mass and heat distribution. Interestingly, these wind‐driven changes are not just products of internal climate variability; most of the observed patterns are recovered by global climate model projections driven by historical anthropogenic forcings, and single‐forcing experiments provide further insight into which forcings are responsible for various features in the satellite altimetry record. Understanding the drivers of regional sea level rise, including differentiating anthropogenic signals from natural variability, is essential for effectively adapting to climate change impacts on global infrastructure and society.

We perform a quadratic extrapolation of sea level on a regional scale based on satellite altimeter observations spanning 1993.0–2023.0, including corrections for natural climate variability, vertical land motion, and a rigorous assessment of the uncertainties associated with serially correlated formal errors, glacial isostatic adjustment, and satellite altimeter measurement errors. The extrapolations are data‐driven and show the trajectory of relative sea level (RSL) over the last 30 years extrapolated into the future. These extrapolations suggest that RSL rise in 2050 relative to 2020 will be 22 ± 5 cm in the North Pacific, 19 ± 6 cm in the North Atlantic, 17 ± 4 cm in the South Atlantic, 15 ± 5 cm in the Indian Ocean, 14 ± 5 cm in the South Pacific, 13 ± 5 cm in the Tropical Pacific, and 12 ± 4 cm in the Southern Ocean. The regional results may differ from each other by more than 80% and differ significantly from the extrapolated global mean sea level rise of 16 ± 4 cm in most cases. The errors in these regional extrapolations are relatively narrow, and we show significant overlap with the regional projections from the most recent IPCC Sixth Assessment Report. The results provide an additional line of evidence when considering how representative the range of climate model projections are in describing near‐term sea level rise and highlight the significance of regional variations in estimates of future sea level.

High‐tide flooding—minor, disruptive coastal inundation—is expected to become more frequent as sea levels rise. However, quantifying just how quickly high‐tide flooding rates are changing, and whether some places experience more high‐tide flooding than others, is challenging. To quantify trends in high‐tide flooding from tide‐gauge observations, flood thresholds—elevations above which flooding begins—must be specified. Past studies of high‐tide flooding in the United States have used different data sets and approaches for specifying flood thresholds, only some of which directly relate to coastal impacts, which has lead to sometimes conflicting and ambiguous results. Here we present a novel method for quantifying, with uncertainty, high‐tide flooding thresholds along the United States coast based on sparsely available impact‐based flood thresholds. We use those newly modeled thresholds to make an updated assessment of changes in high‐tide flooding across the United States over the past few decades. From 1990–2000 to 2010–2020, high‐tide flooding rates almost certainly (probability ) increased along the United States East Coast, Gulf Coast, California, and Pacific Islands, while they very likely decreased along Alaska during that time; significant changes in high‐tide flooding rates between the two decades were not detected in Oregon, Washington, and the Caribbean. Averaging spatially, we find that high‐tide flooding rates probably more than doubled nationally between 1990–2000 and 2010–2020. Our approach lays a foundation for future studies to more accurately model high‐tide flood thresholds and trends along the global coastline.