The need for explicitly considering equity in adaptation planning is increasingly being recognized. However, quantitative evaluations of adaptation options often adopt an aggregated perspective, while disaggregation of results is important to learn about who benefits when and where. A typical example is adaptation of rice agriculture in the Vietnam Mekong Delta. In the past two decades, efforts focused on flood protection have mainly benefitted large-scale farmers while harming small-scale farmers. To investigate the distributional consequences of adaptation policies in the Vietnam Mekong Delta, we assess both aggregate efficiency and equity indicators, as well as disaggregated impacts in terms of district-level farmers profitability. Doing so requires an adequate representation of the co-evolutionary dynamics between the human and environmental systems which influence farmers profitability. We develop a spatially-explicit integrated assessment model that couples inundation and sedimentation dynamics, soil fertility and nutrient dynamics, and behavioral land-use change and farmers profitability calculation. We find that inter-district inequality responds in a non-linear way to climatic and socio-economic changes and choices of adaptation policies. Distinctive inequality patterns emerge from even slightly different combinations of policies and realizations of uncertain futures. We also find that there is no simple ranking of alternative adaptation policies, so one should make trade-offs based on the agreed preferences. Accounting for equity implies exploring the distribution of outcomes over different actor groups over a range of uncertain futures. Only by accounting for multisectoral dynamics can planners anticipate the equity consequences of adaptation options and prepare additional measures to aid the worse-off actors.

Sea-level rise (SLR) is a long-lasting consequence of climate change because global anthropogenic warming takes centuries to millennia to equilibrate. SLR projections based on climate models support policy analysis, risk assessment and adaptation planning today, despite their large uncertainties. The central range of the SLR distribution is estimated by process-based models. However, risk-averse practitioners often require information about plausible future conditions that lie in the tails of the SLR distribution, which are poorly defined by existing models. Here, a community effort combining scientist and practitioners, builds on a framework of discussing physical evidence to quantify high-end global SLR for practice. The approach is complementary to the IPCC AR6 report and provides further physically plausible high-end scenarios. High-end estimates for the different SLR components are developed for two climate scenarios at two timescales. For global warming of +2 ˚C in 2100 (SSP1-2.6) relative to pre-industrial values our high-end global SLR estimates are up to 0.9 m in 2100 and 2.5 m in 2300. Similarly, for +5 ˚C (SSP5-8.5) we estimate up to 1.6 m in 2100 and up to 10.4 m in 2300. The large and growing differences between the scenarios beyond 2100 emphasize the long-term benefits of mitigation. However, even a modest 2 ˚C warming may cause multi-meter SLR on centennial time scales with profound consequences for coastal areas. Earlier high-end assessments focused on instability mechanisms in Antarctica, while we emphasize the timing of ice-shelf collapse around Antarctica, which is highly uncertain due to low understanding of the driving processes.