COASTAL CLIMATE CHANGE ADAPTATION REQUIRES QUANTITATIVE PROBABILISTIC PROJECTIONS OF THE CHANGING RISKS ASSOCIATED WITH SEA-LEVEL RISE BUT SUCH PROJECTIONS ARE HAMPERED BY UNCERTAINTY IN THE FUTURE RESPONSE OF THE GREAT POLAR ICE SHEETS TO A WARMING ATMOSPHERE AND OCEAN. EMERGING SCIENCE HAS SHOWN THE POTENTIAL FOR EXTREME ICE-SHEET RETREAT ON POLICY-RELEVANT TIMESCALES BUT THE UNDERLYING MECHANISMS HAVE YET TO BE ADEQUATELY QUANTIFIED. FURTHER WORK IS NEEDED TO IMPROVE MODEL PHYSICS ESTABLISH RANGES OF STRUCTURAL AND PARAMETRIC UNCERTAINTY AND DEFINE CLIMATIC THRESHOLDS CAPABLE OF TRIGGERING DRASTIC (AND POTENTIALLY IRREVERSIBLE) ICE-SHEET RETREATPARTICULARLY IN THE MARINE-BASED SECTORS OF ANTARCTICA. FURTHERMORE FEEDBACKS BETWEEN ICE SHEETS OCEAN AND THE SOLID EARTH HAVE YET TO BE CONSIDERED COLLECTIVELY AND A COMPREHENSIVE SUITE OF REMOTE SENSING PRODUCTS (JASON ICESAT1 OIB ICESAT-2 CRYOSAT-2 GRACE GRACE-FO AND LANDSAT8) HAVE NOT BEEN LEVERAGED COLLECTIVELY TO IMPROVE MODEL REPRESENTATIONS OF KEY PHYSICAL PROCESSES. TO FACE THE GRAND CHALLENGE OF PREDICTING FUTURE SEA-LEVEL RISE OUR TEAM WILL DEVELOP NEW PROBABILISTIC GLOBAL AND LOCAL SEA-LEVEL PROJECTIONS THAT SMOOTHLY LINK STATE-OF-THE-ART PHYSICAL MODELS WITH OBSERVATIONS OF SEA LEVEL AND ICE SHEET CHANGES. WE WILL REDUCE UNCERTAINTY STEMMING FROM COMPLEX ICE-SHEET GROUNDING ZONE AND ICE-TERMINUS PHYSICS AS WELL AS ICE-OCEAN-ATMOSPHERE-SOLID EARTH FEEDBACKS BY EXTENDING AN ICE SHEET MODEL WITH NEW GLACIOLOGICAL PROCESSES TWO-WAY COUPLING WITH CLIMATE AND EARTH-GRAVITATIONAL MODELS AND SATELLITE-BASED CONSTRAINTS ON MODEL PHYSICS. OUR INTERDISCIPLINARY TEAM WILL DIRECTLY TARGET ALL FOUR NASA SEA LEVEL SCIENCE TEAM OBJECTIVES: 1. BASELINE SEA-LEVEL ANALYSIS (MITROVICA VELICOGNA KOPP): BY COMBINING TIDE-GAUGE DATA OBSERVATIONS OF GLACIAL-ISOSTATIC ADJUSTMENT GRAVIMETRY ALTIMETRY MATHEMATICAL MODELS OF SEA-LEVEL VARIABILITY STATISTICS AND SPACE-GEODETIC CONSTRAINTS ON ICE VOLUMES WE WILL ISOLATE CONTRIBUTIONS FROM INDIVIDUAL SEA-LEVEL SOURCES PROVIDE A FRAMEWORK FOR MONITORING THEIR EVOLUTION AND RECONCILE THEIR GEOGRAPHIC VARIABILITY. 2. PROBABILISTIC ANALYSIS OF LOCAL SEA-LEVEL RISE AND SUPERPOSED EXTREME STORM-TIDE EVENTS (KOPP MITROVICA STRAUSS): A PROBABILISTIC FRAMEWORK FOR ASSIMILATING PROBABILITY DISTRIBUTIONS OF THE DIFFERENT FACTORS CONTRIBUTING TO SEA LEVEL CHANGE (GLOBAL MEAN AND LOCALLY) INCLUDING GLACIERS OCEAN THERMAL EXPANSION/DYNAMICS LAND WATER STORAGE GIA SEA LEVEL FINGERPRINTS AND CORRELATIONS BETWEEN RELATED PROCESSES WILL DRAMATICALLY IMPROVE CHARACTERIZATIONS OF UNDERLYING PROCESSES AND PREDICTIONS OF LOCAL SEA-LEVEL RISE. 3. GREENLAND AND ANTARCTIC ICE SHEET ENSEMBLES WITH NEW OBSERVATIONALLY CONSTRAINED MODEL PHYSICS (DECONTO POLLARD CHRISTIANSON VELICOGNA): GRACE GRAVITY DATA WILL VALIDATE DECADAL TRENDS IN WATER/ICE RESERVOIRS PREDICTED BY OUR CLIMATE AND ICE MODELS. THE COMBINATION OF LEGACY SATELLITE AND AIRBORNE ALTIMETRY DATA AND UPCOMING ICESAT-2 DATA PRODUCTS (ICE SURFACE ELEVATION AND CALVING/ TERMINUS MIGRATION) AND ICE FLOW DATA (INSAR) WILL BE COMBINED WITH OBSERVED TRENDS IN SURFACE MELTWATER (LANDSAT8 SATELLITE SCATTEROMETER) ON ANTARCTICA AND GREENLAND TO DEVELOP MORE PHYSICAL AND OBSERVATIONALLY VALIDATED PARAMETERIZATIONS OF KEY GLACIOLOGICAL PROCESSES INCLUDING CALVING HYDROFRACTURING AND ICE-CLIFF RETREAT. 4. FORECASTS OF SEA-LEVEL RISE (STRAUSS KOPP AND TEAM): FINALLY THE NEW BASELINE SEA-LEVEL ANALYSIS (GOAL 1) PROBABILISTIC ANALYSIS OF LOCAL SEA-LEVEL RISE AND EXTREME STORM-TIDE EXCEEDANCES (GOAL 2) USING ICE SHEET ENSEMBLES WITH IMPROVED OBSERVATIONALLY CONSTRAINED MODEL PHYSICS (GOAL 3) WILL BE INTEGRATED INTO PROBABILISTIC SEA-LEVEL AND STORM-TIDE FORECASTS ON A GLOBAL GRID. THE RESULTS WILL BE MADE UNIVERSALLY ACCESSIBLE THOUGH WEB-BASED OUTREACH TOOLS ALIGNED WITH THE NASA SEA-LEVEL WEB PORTAL EXPRESSLY FOR RISK-BASED DECISION MAKING.