1850-2200 greenland ice sheet smb as simulated by … · 1850-2200 greenland ice sheet smb ... •...
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1850-2200 Greenland ice sheet SMB as simulated by CESM1.1 (CAM5.2)
Miren Vizcaino (1), Leo van Kampenhout (2), Jan Lenaerts (2), Vincent Cabot (1), William Sacks (3)
(1) TU Delft, The Netherlands
(2) IMAU, Utrecht University, The Netherlands (3) NCAR, CO, USA
Contributors to GrIS mass loss Mass anomalies referred to equilibrium (mean 1961-1990 SMB and 1996 ice discharge)
Enderlin et al., GRL, 2014
42% 68%
Projections require SMB & ice flow coupling
• 1st GrIS projections with coupled AOGCM-ISM1 under RCP/ECP
• Elevation change enhances SMB loss by 10% (2100) & 30% (2300)
• Ice discharge decreases due to thinning and retreat from increased surface melt
1 ECHAM5/MPIOM-SICOPOLIS Vizcaino et al., GRL, 2015
GrIS surface mass budget (SMB) Run-off=
Melt+Rainfall-Refreezing Precipitation
= Snowfall+Rainfall SMB=
Precipitation - Ablation
kg m-2 yr-1 1958-2007 means from high-resolution regional climate model RACMO (Ettema et al. GRL, 2009)
SMB from GCMs
• Runoff is underestimated in CMIP5 models
• Deficient snow schemes (e.g., fixed albedo)
Cullather et al., 2014
cm-2 yr-1 w.e.
CESM1.0: 1st realistic GCM simulation of GrIS SMB
“Recipe”: 1. Realistic surface climate 2. Explicit albedo, melt
and refreezing simulation in CLM
3. Downscalling based on SMB calculation at fixed elevations
kg m-2 yr-1
Simulated snowfall minus melt (dots: observations)
Vizcaino et al, J. Clim., 2013 (Evaluation) Vizcaino et al, J. Clim., 2014 (Projections)
Outline
1850-2200 CESM1.1(CAM5.2)/FV1 simulations: • 1960-2005: Present-Day climate and SMB
– LW biases and SMB implications
• RCP2.6 & RCP8.5_4x scenarios • Outlook
Snowfall is well simulated
• Better agreement than in CAM4, specially wet SW & dry N interior
1° 11 km RACMO2.3 is forced with reanalysis
Melt & surface energy budget
• Most of melt energy M comes from surface radiation
• Albedo-melt feedback
13
Downward LW increases 2080-99 minus 1980-99, RCP8.5 (W m-2)
• Higher increase than in CESM1.0, explaining similar SMB by 2100 regardless of high present-day SMB
Net radiation increases
2080-99 minus 1980-99, RCP8.5 • Due to
increased downward LW & reduced albedo
Summary • GrIS surface melt is underestimated in
CESM1.1(CAM5.2) due to insufficient cloud liquid content causing low incoming LW
• GrIS precipitation is well simulated • SMB becomes negative by 2100 in RCP8.5,
similarly to CESM1.0 (CAM4) • SMB modestly decreases by 2100 in RCP2.6 • Further melt increases by 2200 in both scenarios • RCP8.5 beyond 2100 had to be capped at 4xCO2
(code breaks) • We will repeat simulations after surface radiation
budget is improved