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Changes in ocean temperature and salinity are expected to be an important determinant of the Greenland ice sheet's future sea level contribution. Yet, simulating the impact of these changes in continental-scale ice sheet models remains challenging due to the small scale of key physics, such as fjord circulation and plume dynamics, and poor understanding of critical processes, such as calving and submarine melting. Here we present the ocean forcing strategy for Greenland ice sheet models taking part in the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6), the primary community effort to provide 21st century sea level projections for the Intergovernmental Panel on Climate Change Sixth Assessment Report. Beginning from global atmosphere–ocean general circulation models, we describe two complementary approaches to provide ocean boundary conditions for Greenland ice sheet models, termed the “retreat” and “submarine melt” implementations. The retreat implementation parameterises glacier retreat as a function of projected subglacial discharge and ocean thermal forcing, is designed to be implementable by all ice sheet models and results in retreat of around 1 and 15 km by 2100 in RCP2.6 and 8.5 scenarios, respectively. The submarine melt implementation provides estimated submarine melting only, leaving the ice sheet model to solve for the resulting calving and glacier retreat and suggests submarine melt rates will change little under RCP2.6 but will approximately triple by 2100 under RCP8.5. Both implementations have necessarily made use of simplifying assumptions and poorly constrained parameterisations and, as such, further research on submarine melting, calving and fjord–shelf exchange should remain a priority. Nevertheless, the presented framework will allow an ensemble of Greenland ice sheet models to be systematically and consistently forced by the ocean for the first time and should result in a significant improvement in projections of the Greenland ice sheet's contribution to future sea level change., info:eu-repo/semantics/published

The effect of the North Atlantic Ocean on the Greenland Ice Sheet through submarine melting of Greenland's tidewater glacier calving fronts is thought to be a key driver of widespread glacier retreat, dynamic mass loss and sea level contribution from the ice sheet. Despite its critical importance, problems of process complexity and scale hinder efforts to represent the influence of submarine melting in ice-sheet-scale models. Here we propose parameterizing tidewater glacier terminus position as a simple linear function of submarine melting, with submarine melting in turn estimated as a function of subglacial discharge and ocean temperature. The relationship is tested, calibrated and validated using datasets of terminus position, subglacial discharge and ocean temperature covering the full ice sheet and surrounding ocean from the period 1960-2018. We demonstrate a statistically significant link between multi-decadal tidewater glacier terminus position change and submarine melting and show that the proposed parameterization has predictive power when considering a population of glaciers. An illustrative 21st century projection is considered, suggesting that tidewater glaciers in Greenland will undergo little further retreat in a low-emission RCP2.6 scenario. In contrast, a high-emission RCP8.5 scenario results in a median retreat of 4.2 km, with a quarter of tidewater glaciers experiencing retreat exceeding 10 km. Our study provides a long-term and ice-sheet-wide assessment of the sensitivity of tidewater glaciers to submarine melting and proposes a practical and empirically validated means of incorporating ocean forcing into models of the Greenland ice sheet., SCOPUS: ar.j, info:eu-repo/semantics/published

By synthesizing recent studies employing a wide range of approaches (modern observations, paleo reconstructions, and climate model simulations), this paper provides a comprehensive review of the linkage between multidecadal Atlantic Meridional Overturning Circulation (AMOC) variability and Atlantic Multidecadal Variability (AMV) and associated climate impacts. There is strong observational and modeling evidence that multidecadal AMOC variability is a crucial driver of the observed AMV and associated climate impacts and an important source of enhanced decadal predictability and prediction skill. The AMOC-AMV linkage is consistent with observed key elements of AMV. Furthermore, this synthesis also points to a leading role of the AMOC in a range of AMV-related climate phenomena having enormous societal and economic implications, for example, Intertropical Convergence Zone shifts; Sahel and Indian monsoons; Atlantic hurricanes; El Niño–Southern Oscillation; Pacific Decadal Variability; North Atlantic Oscillation; climate over Europe, North America, and Asia; Arctic sea ice and surface air temperature; and hemispheric-scale surface temperature. Paleoclimate evidence indicates that a similar linkage between multidecadal AMOC variability and AMV and many associated climate impacts may also have existed in the preindustrial era, that AMV has enhanced multidecadal power significantly above a red noise background, and that AMV is not primarily driven by external forcing. The role of the AMOC in AMV and associated climate impacts has been underestimated in most state-of-the-art climate models, posing significant challenges but also great opportunities for substantial future improvements in understanding and predicting AMV and associated climate impacts.

The first New Jersey Science and Technical Advisory Panel (STAP) on Sea-Level Rise and Coastal Storms was convened by Rutgers University on behalf of the NJ Climate Change Alliance in 2015, culminating in a 2016 report that identified planning options for practitioners to enhance the resilience of New Jersey’s people, places, and assets to sea-level rise, coastal storms, and the resulting flood risk (Kopp et al., 2016). An innovative approach used to inform the 2016 report was the complementary convening of a panel of practitioners to offer insights on the application of the STAP science to state and local planning and decision-making. Following the same process, the same team at Rutgers University was engaged by the State of New Jersey Department of Environmental Protection to update the 2016 report based on the most current scientific information. Similar to the inaugural work, the 2019 STAP was charged with identifying and evaluating the most current science on sea-level rise projections and changing coastal storms, considering the implications for the practices and policies of local and regional stakeholders, and providing practical options for stakeholders to incorporate science into risk-based decision processes. The 2019 STAP process recommended the following key updates to the 2016 STAP report: Making available historical sea-level rise (SLR) information for New Jersey to provide a frame of reference for future projections; Updating information on ice sheet dynamics; Expanding consideration of tidal flooding; and Expanding consideration of storm tide-related flooding. This report integrates the 2019 key STAP updates and should be considered the most recent reference in this series.

The ongoing emission of greenhouse gases (GHGs) is triggering changes in many climate hazards that can impact humanity. We found traceable evidence for 467 pathways by which human health, water, food, economy, infrastructure and security have been recently impacted by climate hazards such as warming, heatwaves, precipitation, drought, floods, fires, storms, sea-level rise and changes in natural land cover and ocean chemistry. By 2100, the world’s population will be exposed concurrently to the equivalent of the largest magnitude in one of these hazards if emmisions are aggressively reduced, or three if they are not, with some tropical coastal areas facing up to six simultaneous hazards. These findings highlight the fact that GHG emissions pose a broad threat to humanity by intensifying multiple hazards to which humanity is vulnerable.

Future coastal flood risk will be strongly influenced by: 1) sea level rise (SLR) and 2) changes in the frequency and intensity of tropical cyclones (TCs). These two factors are generally considered independently. Here, we assess 21st century changes in the United States East Coast hazard using a flood index (FI) that accounts for changes in flood duration and magni- tude driven by SLR and changes in Power Dissipation Index (PDI, an integrated measure of TC intensity, frequency, and duration). SLR and PDI are derived from representative con- centration pathway (RCP) simulations of 15 atmosphere-ocean general circulation models (AOGCMs). By 2080-2099, changes in the FI relative to 1986-2005 are substantial and posi- tively skewed: a 10th-90th percentile range of 4-75�� higher in RCP 2.6 and 35-350�� higher for RCP 8.5. High-end FI projections are driven by three AOGCMs that project the largest increases in SLR, PDI, and upper ocean temperatures. Changes in PDI are particularly in- fluential if their intra-model correlation with SLR is included, increasing the RCP 8.5 90th percentile FI by an additional 25%. SLR arising from other, possibly correlated, climate processes (e.g. ice sheet and glacier mass changes) will further increase coastal flood risk and should be accounted for in comprehensive assessments.

Sea‐level rise due to both climate change and non‐climatic factors threatens coastal settlements, infrastructure, and ecosystems. Projections of mean global sea‐level (GSL) rise provide insufficient information to plan adaptive responses; local decisions require local projections that accommodate different risk tolerances and time frames and that can be linked to storm surge projections. Here we present a global set of local sea‐level (LSL) projections to inform decisions on timescales ranging from the coming decades through the 22nd century. We provide complete probability distributions, informed by a combination of expert community assessment, expert elicitation, and process modeling. Between the years 2000 and 2100, we project a very likely (90% probability) GSL rise of 0.5–1.2 m under representative concentration pathway (RCP) 8.5, 0.4–0.9 m under RCP 4.5, and 0.3–0.8 m under RCP 2.6. Site‐to‐site differences in LSL projections are due to varying non‐climatic background uplift or subsidence, oceanographic effects, and spatially variable responses of the geoid and the lithosphere to shrinking land ice. The Antarctic ice sheet (AIS) constitutes a growing share of variance in GSL and LSL projections. In the global average and at many locations, it is the dominant source of variance in late 21st century projections, though at some sites oceanographic processes contribute the largest share throughout the century. LSL rise dramatically reshapes flood risk, greatly increasing the expected number of “1‐in‐10” and “1‐in‐100” year events.