The methods used to generate process-based global and local mean sea-level projections have evolved substantially over the last fifteen years, including improved process understanding, advances in ice-sheet modelling, the use of emulators and further development of high-end scenarios. During this time, two sets of UK national sea-level projections have been generated as part of the UK Climate Projections in 2009 (UKCP09; Lowe et al 2009) and in 2018 (UKCP18; Palmer et al 2018b). UKCP18 presented local mean sea-level projections for the UK coastline for the 21st century rooted in Coupled Model Intercomparison Project Phase 5 (CMIP5) models and in methods used in the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5), with an emulator-based methodology to provide extended projections to 2300 (Palmer et al 2018a; 2020). We compare UKCP18 global and local mean sea-level projections with those presented in the IPCC Sixth Assessment Report (AR6, IPCC 2021a). We find the likely range projections (characterising the central two-thirds of the distribution) are broadly similar at 2150 to within 0.1 m, except at Edinburgh, where the maximum difference is 0.22 m under medium emissions. Differences arise due to higher contributions from sterodynamic processes and the Antarctic ice sheet, and higher or lower vertical land movement, in AR6 compared to UKCP18. We also compare high-end sea-level rise estimates, presented in AR6 and UKCP09, finding reasonable global and UK local agreement over the 21st century. We explore future paths for UK sea-level science considering both user needs for information and developments in modelling capability. Future UK sea-level projections would benefit from updated high-end sea-level rise scenarios which extend beyond 2100 and continued efforts to build understanding of observed sea-level change drivers. Alongside close collaboration with user groups this would enhance the utility of local sea-level projections by UK coastal practitioners and decision-makers.

Pakistan is vulnerable to a range of climate hazards, including sea-level rise. The Indus Delta region, situated in the coastal Sindh province, is particularly at risk of sea-level rise due to low-lying land and fragile ecosystems. In this article, expertise is drawn together from the newly established Pakistan Sea-Level Working Group, consisting of policy experts, scientists, and practitioners, to provide recommendations for future research, investment, and coastal risk management. An assessment of the current scientific understanding of sea-level change and coastal climate risks in Pakistan highlights an urgent need to improve the availability and access to sea-level data and other coastal measurements. In addition, reflecting on the policy environment and the enablers needed to facilitate effective responses to future sea-level change, recommendations are made to integrate coastal climate services into the National Adaptation Plan and develop a National Framework for Climate Services. Such a framework, alongside collaboration, co-production, and capacity development, could help support required improvements in coastal observations and monitoring and continuously deliver useful, usable, and accessible sea-level information for use by practitioners and decision-makers.

The northwest European shelf (NWS) seas are environmentally and economically important, and an understanding of how their climate may change helps with their management. However, as the NWS seas are poorly represented in global climate models, a common approach is to dynamically downscale with an appropriate shelf sea model. We develop a set of physical marine climate projections for the NWS. We dynamically downscale 12 members of the HadGEM3-GC3.05 perturbed parameter ensemble (approximately 70 km horizontal resolution over Europe), developed for UKCP18, using the shelf sea model NEMO CO9 (7 km horizontal resolution). These are run under the RCP8.5 high-greenhouse-gas-emission scenario as continuous simulations over the period 1990–2098. We evaluate the simulations against observations in terms of tides, sea surface temperature (SST), surface and near-bed temperature and salinity, and sea surface height. These simulations represent the state of the art for NWS marine projections. We project an SST rise of 3.11 °C (± 2σ = 0.98 °C) and a sea surface salinity (SSS) freshening of −1.01 (± 2σ = 0.93; on the (unitless) practical salinity scale) for 2079–2098 relative to 2000–2019, averaged over the NWS (approximately bounded by the 200 m isobar and excluding the Norwegian Trench, the Skagerrak and Kattegat), a substantial seasonal stratification increase (23 d over the NWS seas), and a general weakening of the NWS residual circulation. While the patterns of NWS changes are similar to our previous projections, there is a greater warming and freshening that could reflect the change from the A1B emissions scenario to the RCP8.5 concentrations pathway or the higher climate sensitivity exhibited by HadGEM3-GC3.05. Off the shelf, south of Iceland, there is limited warming, consistent with a reduction in the Atlantic Meridional Overturning Circulation and associated northward heat transport. These projections have been publicly released, along with a consistent 200-year present-day control simulation, to provide an evidence base for climate change assessments and to facilitate climate impact studies. For example, we illustrate how the two products can be used to estimate climate trends, unforced variability and the time of emergence (ToE) of the climate signals. We calculate the average NWS SST ToE to be 2034 (with an 8-year range) and 2046 (with a 33-year range) for SSS. We also discuss how these projections can be used to describe NWS conditions under 2 and 4 °C global mean warming (compared with 1850–1900), as a policy-relevant exemplar use case.

Local projections of future sea-level change are important for understanding climate change risks and informing coastal management decisions. Reliable and relevant coastal risk information is especially important in South Asia, where large populations live in low-lying areas and are at risk from coastal inundation. We present a new set of local sea-level projections for selected tide gauge locations in South Asia. The projections are used to explore the drivers of spatial variations in sea-level change for South Asia over the 21st century under the RCP2.6 and RCP8.5 scenarios. Global sea-level rise for 2081–2100 is projected to be 0.39 m (0.26–0.58 m) and 0.65 m (0.47 m–0.93m) for RCP2.6 and RCP8.5 respectively. Local sea-level rise projections for the same period vary spatially over the South Asia region, with local sea-level rise in excess of projected global sea-level rise in the equatorial Indian Ocean but less than projected global sea-level rise for the northern Arabian Sea and northern Bay of Bengal. Local sea-level rise for 2081–2100 is projected to be 0.44 m (0.29–0.67 m) and 0.72 m (0.51–1.06 m) at Gan II (Maldives) under RCP2.6 and RCP8.5 respectively, whereas for Diamond Harbour (West Bengal) the corresponding changes are 0.32 m (0.19–0.51 m) and 0.57 m (0.39–0.85m). We find that the sterodynamic contribution is generally the leading driver of change at any single location, with future groundwater extraction over the sub-continent landmass the main driver of spatial variations in sea-level across the region. The new localised projections quantify and enhance understanding of future sea-level rise in South Asia, with the potential to feed into decisions for coastal planning by local communities, government, and industry.

We present a framework for developing storylines of UK sea level rise to aid risk communication and coastal adaptation planning. Our approach builds on the UK national climate projections (UKCP18) and maintains the same physically consistent methods that preserve component correlations and traceability between global mean sea level (GMSL) and local relative sea level (RSL). Five example storylines are presented that represent singular trajectories of future sea level rise drawn from the underlying large Monte Carlo simulations. The first three storylines span the total range of the Intergovernmental Panel on Climate Change (IPCC) Sixth Assessment Report (AR6) likely range GMSL projections across the SSP1-2.6 and SSP5-8.5 scenarios. The final two storylines are based upon recent high-end storylines of GMSL presented in AR6 and the recent literature. Our results suggest that even the most optimistic sea level rise outcomes for the UK will require adaptation of up to 1 m of sea level rise for large sections of coastline by 2300. For the storyline most consistent with current international greenhouse gas emissions pledges and a moderate sea level rise response, UK capital cities will experience between about 1 and 2 m of sea level rise by 2300, with continued rise beyond 2300. The storyline based on the upper end of the AR6 likely range sea level projections yields much larger values for UK capital cities that range between about 3 and 4 m at 2300. The two high-end scenarios, which are based on a recent study that showed accelerated sea level rise associated with ice sheet instability feedbacks, lead to sea level rise for UK capital cities at 2300 that range between about 8 m and 17 m. These magnitudes of rise would pose enormous challenges for UK coastal communities and are likely to be beyond the limits of adaptation at some locations.