Transcript Document

Toward Advanced Understanding and Prediction
of Arctic Climate Change
Wieslaw Maslowski
Naval Postgraduate School
34th Annual Climate Diagnostics and Prediction Workshop, Monterey, CA, 26-30 October, 2009
Outline
• Model predictions of Arctic ice extent
• Trends of melt rates based on Ice extent vice
ice thickness and volume
• Atmospheric vice Oceanic forcing of local
sea ice melt
• Future projections of ice melt
• Regional Arctic Climate System Model
Observed Rate of Loss Faster Than GCM Predicted
Obs 79-00 Mean = 7.0 Mln km2
SSM/I
period
Adapted from Stroeve et al., 2007
• Wang & Overland, 2009: Ice-free summer Arctic Ocean by 2037
• "A linear increase in heat in the Arctic Ocean will result in a non-linear and
accelerating loss of sea ice.“ - Norbert Untersteiner, Prof. Emeritus, Univ. of Washington, July 2006
Observed Arctic sea ice extent (a,b) and modeled sea ice
thickness (c,d) during September 1979 (a,c) and 2002 (b,c)
09/79
09/02
a)
b)
c)
d)
SSM/I – 2D
MODEL - 3D
Significant decrease
in observed sea ice
extent (17-20%; top)
and in modeled ice
thickness (up to 1.52.0 m or ~35%;
bottom) in the 2000s.
Note that largest
changes are
downstream of
Pacific / Atlantic
water inflow into the
Arctic Ocean.
(Maslowski et al., 2007)
Observed MY Ice Fraction
Forcing of Arctic sea ice melt
• “Atmospheric circulation trends are weak over the record as a
whole, suggesting that the long-term retreat of Arctic sea ice since
1979 in all seasons is due to factors other than wind-driven
atmospheric thermal advection.” - Deser and Teng, J. Clim. 2008
• Oceanic Forcing can locally play critical role in melting sea ice via:
– horizontal advection of warm Pacific / Atlantic water into/under the sea
ice cover (e.g. Stroeve and Maslowski, 2007)
– Locally induced (upwelling, topographically controlled flow, eddies)
upward heat flux into the mixed layer
(Maslowski and Clement Kinney, in review, 2009)
1979-2004 Mean Oceanic Heat Convergence: 0-120 m; Tref = Tfreezing
Modeling Challenges:
Inflow of Pacific / Atlantic
Water into the Arctic Ocean
Heat Loss
Heat Loss
FSBW
• Pacific Water entering via
narrow (~60mi) Bering Strait
• outflow through Fram
Strait vs. Atlantic Water
inflow (FSBW)
Heat Loss
• Atlantic (BSBW) and Pacific
Water each losses majority
of heat to the atmosphere
before entering Arctic Basin
Arctic ocean-ice-atm
feedbacks – not represented
realistically in climate models
High resolution is one of the top requirements for advanced modeling of Arctic climate
(Maslowski and Clement Kinney, 2009; Maslowski et al., 2008, Clement et al., 2005)
Modeled Oceanic heat flux exiting the Chukchi Shelf
E
W
Chukchi Shelf Line
Chukchi Line 2
Sept. 1984
Chukchi
Line 1
Sept. 2002
Heat Flux via Alaska Coastal
Current accounts for ~67% of
the Total Heat Flux across
Chukchi Shelf Line
Modeled Upper Ocean Heat Content and Ice Thickness Anomalies
(Mean Annual Cycle Removed)
Heat content accumulated
in the sub-surface ocean
since mid-1990s explains
at least 60% of total sea
ice thickness change
Intrusion of oceanic heat
into the mixed layer due
to anti-cyclonic eddies
Temperature above freezing (oC)
and velocity (cm/s) is shown in the
top four panels.
Potential density (σθ) and velocity
(cm/s) profiles are shown in the
lower four panels.
The vertical section locations are
shown by the black and red lines,
which are across the Chukchi Rise
and Eddy 2.
Area (x107km2)
79-04 time series of Ice Volume, Area, Mean Thickness
Between 1997-2004:
- annual mean sea ice
concentration has
decreased by ~17%
- mean ice thickness has
decreased by ~0.9 m
or ~36%
- ice volume decreased by
40%, which is ~2.5x the
rate of ice area decrease
Volume (x104km3)
If this trend persists the Arctic Ocean
will become ice-free by ~2013!
Need for Regional
Arctic Climate System Model
• There are large errors in global climate system
model simulations of the Arctic climate system
• Observed rapid changes in Arctic climate system
– Sea ice decline
– Greenland ice sheet
– Temperature
• Arctic change has global consequences
– Sea ice change can alter the global energy
balance and thermohaline circulation
Regional Arctic Climate System Model
(RAMC)
Participants:
Wieslaw Maslowski
- Naval Postgraduate School
John Cassano
- University of Colorado
William Gutowski
- Iowa State University
Dennis Lettenmeier
- University of Washington
Other collaborators:
David Bromwich
- OSU
Greg Newby, Andrew Roberts, Juaxion He -UAF/IARC/ARSC
Primary science objective: to synthesize understanding of past and
present states and thus improve decadal to centennial prediction of
future Arctic climate and its influence on global climate.
DOE Climate Change Prediction Program Funded Project
Science Objectives
• Perform multi-decadal simulations to:
– Gain improved understanding of coupled Arctic
climate system processes responsible for
changes in
• Arctic sea ice cover
• hydrologic cycle
• freshwater export
– Improve predictions of Arctic climate change
– Identify limitations and physical and numerical
requirements of global climate system model
simulations of Arctic
RACM components and resolution
•
•
•
•
•
Atmosphere - Polar WRF
Land Hydrology – VIC
Ocean - LANL/POP
Sea Ice - LANL/CICE
Flux Coupler – NCAR CPL7
(gridcell ≤50km)
(same as WRF)
(gridcell ≤10km)
(same as POP)
Use NCAR CCSM4 framework for developing RACM
Higher component resolutions to be evaluated subject
to availability of computer resources
RACM model domain and elevations
Pan-Arctic region to include:
- all sea ice covered ocean in the northern hemisphere
- Arctic river drainage
- critical inter-ocean exchange and transport
- large-scale atmospheric weather patterns (AO, NAO, PDO)
Accomplishments to Date
• 2nd year of 4 year DOE funded project
• Coupled individual model components
to CPL7 and full RACM testing
• Model component evaluation studies
– Polar WRF development and climatology
– Polar WRF and fractional sea ice
– Simulation of sea ice loss with POP/CICE
– Oceanic heat transport
Next Steps
• Finalize component model / CPL7 coupling
• Fully coupled simulations
• Evaluation of fully coupled model
• Multi-decadal retrospective and future climate
simulations
• Long-term goals
– Regional simulations for next IPCC report
– Additional climate system components
• Ice sheets
• Biogeochemistry
Conclusions
1.
2.
3.
4.
5.
Oceanic heat advection / storage has contributed
significant forcing (>60%) to local sea ice melt during
the last decade
Ice-edge & shelf/slope upwelling, eddies and other
mesoscale circulation features in the Canada Basin
provide a mechanism for horizontal heat distribution
throughout the basin and up into the mixed layer
Oceanic heat accumulating in the western Arctic is
potentially a critical initial factor in reducing ice
concentration / thickness before & during the melt
season
The rate of melt of sea ice volume possibly much
greater than that of sea ice extent
A regional high-resolution Arctic Climate System
Model can address these deficiencies and improve
predictive skill of climate models