Jan Lenaerts Utrecht University University of Colorado Ice sheet freshwater forcing Photo: Reijmer, 2011
Sea level meeting 5 to ~6 pm, South Bay Goal: Sea level rise and its impacts on coastal populations are of great relevance to science and society. We are seeking to discuss current and planned activities at interested institutions and projects in order to find potential points of cross-fertilization and cross-institutional collaboration, aimed at improving the decision relevance of climate science in this area. Agenda: Informal discussion of participants' interests, and current and planned activities. Discussion of relevant institutional strategic plans in this area. Brainstorming of potential avenues for information sharing, collaborative activities, etc.
Arctic ocean freshwater balance Liquid freshwater reservoir Sea ice reservoir and fluxes Land and atmosphere input Oceanic FW fluxes Haine et al., 2015
Recent Arctic ocean freshwater changes Haine et al., 2015
Greenland ice sheet changes Åsa Rennermalm (CESM winter meeting) 19% of total freshwater flux
Greenland freshwater forcing (FWF) GrIS FWF: CALVING + RUNOFF 1000 km 3 yr -1 Impact on MOC and global climate (Rahmstorf et al., 2015) Requires land (ice)-atmosphere-ocean, global modeling framework Unrealistic(ally high) hosing CMIP5: poor representation of GrIS no ice dynamics no ice sheet mass loss Bamber et al., 2012 6
GrIS FWF in CESM1 RCP 8.5, best FWF historical, CESM FWF historical, best FWF RCP 8.5, CESM1 FWF RCP 2.6, best FWF RCP 2.6, CESM1 FWF Lenaerts et al., 2015 (GRL) 7
GrIS FWF in CESM1 RCP 8.5, best FWF historical, CESM FWF historical, best FWF RCP 8.5, CESM1 FWF RCP 2.6, best FWF RCP 2.6, CESM1 FWF Lenaerts et al., 2015 (GRL) Historical FWF is well simulated by
GrIS FWF in CESM1 RCP 8.5, best FWF historical, CESM FWF historical, best FWF RCP 8.5, CESM1 FWF RCP 2.6, best FWF RCP 2.6, CESM1 FWF Lenaerts et al., 2015 (GRL) Scenario-dependent and large differences in future FWF
Impact on climate (RCP 8.5, 2060-2090) With CESM FWF Near-surface temperature increase [K] With best FWF Lenaerts et al., 2015 (GRL) 10
Ice sheet FWF in CESM (without ice sheet) CALVING + RUNOFF Immediate ice runoff of solid precipitation (snowfall) Discharged into nearest ocean grid point Spatiotemporal distribution depends on snowfall patterns Surface runoff from snow and ice melt Routed through river runoff model Spatial distribution depends on melt patterns
Ice sheet FWF in CESM (with ice sheet) CALVING + RUNOFF Solid ice calving from ice sheet model (CISM) Surface mass balance Surface runoff from snow and ice melt Routed through river runoff model Spatial distribution depends on melt patterns
Ice sheet FWF in CESM (with ice sheet) CALVING + RUNOFF Solid ice calving from ice sheet model (CISM) Surface runoff from snow and ice melt Routed through river runoff model Surface mass balance Spatial distribution depends on melt patterns End result of atmospheric mass input and snow/firn
What about CESM2? We don t know yet! But we can look at an existing 20 th century simulation
Annual freshwater forcing time series CESM 1.99 Best estimate Liquid phase Solid phase CESM 1.99 Best estimate Within variability, too high sensitivity to warming (?) Signal of excessive solid precipitation
Seasonal cycle Liquid phase Solid phase CESM 1.99 Best estimate CESM 1.99 Best estimate Suppressed seasonal cycle Influence of liquid precipitation in winter! Signal of solid precipitation
Conclusions Ice sheets contribute significantly to high latitude ocean freshwater balance CESM1 showed realistic historical Greenland ice sheet freshwater forcing Model fails to represent ice sheet mass loss (ice sheet- climate interactions needed!) (Preliminary) CESM2 FWF analysis reveals atmospheric model biases over Greenland: excessive (liquid and solid) precipitation Thanks! Jan.Lenaerts@colorado.edu @lenaertsjan