Progress in climate-glacier-ice sheet modelling

Jeremy Fyke (LANL)Bill Lipscomb (LANL)

Bill Sacks (NCAR)Valentina Radic (UBC, Canada)

Synopsis

• RCP8.5 Greenland Ice Sheet (GIS) sea level rise contribution predictions

• Glacier model initialization on RASM model grid

• Preliminary techniques for non-GIS surface mass balance evaluation

• Ongoing work

RCP8.5 GIS sea level rise contribution predictions (Lipscomb et al., submitted)

• Optimized Greenland Ice Sheet preindustiral spin up simulations forced with CESM-derived RCP8.5 surface mass balance to year 2100.

• Best initial GIS configurations generate 7.3 cm of eustatic sea level rise (SLR) 1850-2100

RCP8.5 GIS sea level rise contribution predictions

• Negative feedback between ice thickness and ice velocity strongly damps total SLR signal

RCP8.5 GIS sea level rise contribution predictions

RCP8.5 GIS sea level rise contribution predictions

• Variability in ablation dominates overall SMB variability (+ increase in future variability?)

• ‘Poorly’ optimized models generate different SLR curves

• Due to interplay between hypsometry (area-elevation relationship) of GIS realization ice surface and ablation/discharge

• Improved spinup techniques and reduction of geometry (i.e. preindustrial SMB) biases = important

RCP8.5 GIS sea level rise contribution predictions

Surface mass balance model initialization on climate model grids

• Distributed glacier model component requires an initial glacier population on climate model grid

• Each glacier forced with output from climate model grid-cell SMB

• Recall: each glacier evolved forward using volume-area scaling

• Development of initial conditions for glacier models in RASM has been latest focus

Surface mass balance model initialization on climate model grids

• Randolph Glacier Inventory (v.2) shapefiles + 30-m SRTM/ASTER DEMs processing extended to provide global-coverage high-resolution glacial hypsometries

Nor

mal

ized

hyps

omet

ry

Normalized elevation

• Randolph Glacier Inventory (v.2) shapefiles + 30-m SRTM/ASTER DEMs processing extended to provide global-coverage high-resolution glacial hypsometries

Surface mass balance model initialization on climate model grids

Iceland

Surface mass balance model initialization on climate model grids

• Characteristic shape of normalized hypsometries is motivating some side-line glaciological work – interesting spin-off of model development

Western Canada/US

Surface mass balance model initialization on climate model grids

• Characteristic shape of normalized hypsometries is motivating some side-line glaciological work – interesting spin-off of model development

Svalbard

Surface mass balance model initialization on climate model grids

• Characteristic shape of normalized hypsometries is motivating some side-line glaciological work – interesting spin-off of model development

Scandinavia

Surface mass balance model initialization on climate model grids

• Characteristic shape of normalized hypsometries is motivating some side-line glaciological work – interesting spin-off of model development

Greenland Periphery

Surface mass balance model initialization on climate model grids

• Characteristic shape of normalized hypsometries is motivating some side-line glaciological work – interesting spin-off of model development

Arctic Canada (South)

Surface mass balance model initialization on climate model grids

• Characteristic shape of normalized hypsometries is motivating some side-line glaciological work – interesting spin-off of model development

Arctic Canada (North)

Surface mass balance model initialization on climate model grids

• Characteristic shape of normalized hypsometries is motivating some side-line glaciological work – interesting spin-off of model development

Alaska

• Characteristic shape of normalized hypsometries is motivating some side-line glaciological work – interesting spin-off of model development

Surface mass balance model initialization on climate model grids

Russian Arctic

Surface mass balance model initialization on climate model gridsAn

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-mea

n PD

D a

t mea

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acie

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vatio

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Annual-mean total precipitation

• RGI glaciers nearest-neighbour-binned to RASM grid cells

Surface mass balance model initialization on climate model grids

Surface mass balance model initialization on climate model grids

• 6% of RASM land cells contain initial glacial ice• Land-terminating, ‘non-trivial’ glaciers/ice caps cover

approximately 0.3% of the RASM land surface

Surface mass balance model initialization on climate model grids

• Individual glaciers binned on grid-cell basis

Surface mass balance model initialization on climate model grids

• Empirically, observed ELA occurs where accumulation area=0.57*total area

ELAAccumulation

Ablation

CESM non-GIS surface mass balance evaluation

• Simulated SMB fields need to be compared against against RGI-derived hypsometry

• ELA (line of net 0 ice gain/loss) useful as a composite indicator of T/P conditions: give a new glaciologically-relevant metric of model performance: vertical ELA bias

• Evaluation completed around Greenland peripheral glaciers in CESM

Individual glacierranges in CESM cell

Integrated gridcell hypsometry

CESM SMBprofile

CESM non-GIS surface mass balance evaluation

CESM non-GIS surface mass balance evaluation

Individual glacierranges in CESM cell

Integrated gridcell hypsometry

CESM SMBprofile

CESM non-GIS surface mass balance evaluation

Individual glacierranges in CESM cell

Integrated gridcell hypsometry

CESM SMBprofile

CESM non-GIS surface mass balance evaluation

meltingglaciers

growingglaciers

CESM non-GIS surface mass balance evaluation

• Conclusions– ELA bias a strict indicator of model performance– Bias integrates T and P signal: correlating ELA bias to

(seasonal) T/P biases or land surface biases way forward for assessing REASON for bias

– RASM grid reaches 30N: if all glaciers to be modelled well, sub-grid VIC SMB scheme should work from near-sea-level to above 5000 m, at <=100 m vertical resolution

– RASM may improve on CESM significantly w/r/t ELA biases and glacier simulation due to higher resolution topography

CESM non-GIS surface mass balance evaluation

Ongoing work

• Topography dataset generation underway for set of CAM5.2-SE AMIP-style simulations (collab with Peter Lauritzen), using GIS topographies from Fyke (PhD thesis, 2011)

• Results will guide dynamic coupling of ice sheet with atmosphere models

• Transient spin-up techniques:– CESM has been run to quasi-equilibrium under

LGM/mid-Holocene/preindustrial conditions– Extensions of these simulations with SMB calculations

turned on should provide end-members for a transient glacial spin-up for model using ice core isotope data as control on interpolation

Holocene

LGM

time

Ongoing work

Ongoing work

• Further development of CESM SMB scheme:– Refinement of vertical SMB calculations to capture high-

elevation glaciers (Fyke/Sacks)– Dynamic land units for ice sheet/glacier retreat (Sacks)– Wrapping glacier and ice sheet model into ‘glc’ land

surface model component (Sacks)– Isolating climate-ELA biases (Fyke/Radic): forcing CLM

model with CAM/re-analysis• Further refinement of statistical glacier scheme:– Simulation of size distribution vs. individual glaciers– Parameterization of ice retreat at terminus

Thanks!