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Seymour Laxon2nd Envisat Summer School
Are the Ice caps melting?
Seymour LaxonCentre for Polar Climate and Modelling,
University College London
•Greenland•Antarctica•Arctic sea ice
Seymour Laxon2nd Envisat Summer School
Ice Sheet Mass Balance -2
Seymour Laxon2nd Envisat Summer School
Summer Melting
Wet Snow Zone Wet Snow Zone
Percolation Zone Percolation Zone
Seymour Laxon2nd Envisat Summer School
Ice Sheet Melt Duration - ERS Scatterometer
Courtesy I. Ashcraft, BYU
Seymour Laxon2nd Envisat Summer School
Laser vs. ERS Altimeter-derived dH/dt
Courtesy W. Krabill Courtesy Wingham, UCL
ERS-2: 1995 - 2000
1978 - 1988Geosat - Seasat
Davis et al. 2001
PARCA ATM flights 1993-1997
* Little change in Central Greenland – spatial variations associated with dA/dt
* Dramatic changes in periphery of ice– sheet attributable to a combination of dynamic changes and melting
Seymour Laxon2nd Envisat Summer School
Ice Sheet Elevation
Seymour Laxon2nd Envisat Summer School
Ice Sheet Elevation Change
Seymour Laxon2nd Envisat Summer School
Seymour Laxon2nd Envisat Summer School
Ice Sheet Flow - SAR Interferometry
Seymour Laxon2nd Envisat Summer School
Ice Sheet Flow - SAR Interferometry
Seymour Laxon2nd Envisat Summer School
Ice Sheet Flow
[JPL]
Seymour Laxon2nd Envisat Summer School
Ice Area and Concentration trend• 20 year period
indicates reduction of 3%/decade in ice area
• Quasi periodic fluctuations evident with 3-5 year period
• Regional trends vary significantly
• Most pronounced 10% decrease in Kara and Barents Seas
Courtesy Zwally et al. (2002)
Seymour Laxon2nd Envisat Summer School
Changes in minimum extent since 1979
QuickTime™ and aYUV420 codec decompressorare needed to see this picture.
Seymour Laxon2nd Envisat Summer School
Yearly Anomalies of the Perennial
Ice Cover:1979 to 2003
J. Comiso, GRL, 2002
Seymour Laxon2nd Envisat Summer School
Twelve-year averages in the perennial ice cover
and change map
The actual area changed by about 12 % from one period to the other indicating a 10% decadal change
Seymour Laxon2nd Envisat Summer School
Warming Trends from Satellite Infrared Data
• Inside 60oN, the trends are highest in North American and Europe
• Trends are moderate in the Central Arctic because of upper limits in sea ice temperature
• Trends are slightly negative in parts of Russia and Greenland.
• Data also indicates increases in melt period of 9 to 17 days per decade over sea ice, Eurasia, Greenland, and North America.
Ref. Comiso, J. Climate, Nov. 2003
Seymour Laxon2nd Envisat Summer School
Trends in the Perennial Ice (1979-2003)and Surface Temperature (1981-2002)
Ref. Comiso, GRL, 2002
Seymour Laxon2nd Envisat Summer School
Seymour Laxon2nd Envisat Summer School
QuickTime™ and a decompressor
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Seymour Laxon2nd Envisat Summer School
Arctic Sea Ice : 40% thinning in just 30 years!
Seymour Laxon2nd Envisat Summer School
On both sides of the Arctic!
Seymour Laxon2nd Envisat Summer School
Submarine Trends
Rothrock, et al., 2003, JGR.
Seymour Laxon2nd Envisat Summer School
Tucker et. al., GRL, 2001
1950
2050
• Significant thinning in the Western Arctic but not at the North Pole
Seymour Laxon2nd Envisat Summer School
(Winsor, GRL, 2001)
1950
2050
Seymour Laxon2nd Envisat Summer School
Arctic Ice Thinning - Computer Models
Seymour Laxon2nd Envisat Summer School
Arctic Ice Thinning - Computer Models
Holloway, et al. , J. Clim., 2001.
Seymour Laxon2nd Envisat Summer School
Inter-annual Variability of Ice Thickness
Seymour Laxon2nd Envisat Summer School
Inter-annual Variability of Ice Thickness
Seymour Laxon2nd Envisat Summer School
Sea Ice Dynamic and ThermodynamicsThermodynamics
Dynamics
Perovich, Ann, Glaciol., 2001.
Seymour Laxon2nd Envisat Summer School
∂gdt
= −∂( fg)
∂h− div(Ug) + ψ + φ
Dynamic and Thermodynamic control of ice thickness
Seymour Laxon2nd Envisat Summer School
Courtesy Mark Hopkins
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Ice Ridging
Seymour Laxon2nd Envisat Summer School
Arctic Oscillation (AO)
2050
AO Index 1958-2000AO Index 1958-2000
Seymour Laxon2nd Envisat Summer School
AO Index 1958-2000
Seymour Laxon2nd Envisat Summer School
Arctic Ocean Oscillation (AOO)
Seymour Laxon2nd Envisat Summer School
AOO Index 1946-2000
Seymour Laxon2nd Envisat Summer School
Hilmer and Lemke, GRL, 2000
1950
2050
• Numerical simulations suggest the submarine trends may be an artefact of the areas and years when the data are collected, overall Arctic trend is - 4% / decade
Seymour Laxon2nd Envisat Summer School
Ice Thickness Simulations (1950 - 2000)
Rothrock, et al., JGR, 2003.
Seymour Laxon2nd Envisat Summer School
Questions?
• Are the submarine trends due to natural variations in the ice cover or are they a signal of climate change?
• Are the observed changes simply due to changes in wind and ocean circulation?
• How good are the model simulations?
Seymour Laxon2nd Envisat Summer School
Freeboard
h =ct2
Satellite Altimetry - Measurement Principle
Seymour Laxon2nd Envisat Summer School
Geosat 1985 -
Seymour Laxon2nd Envisat Summer School
ERS-1 1991-
Seymour Laxon2nd Envisat Summer School
ERS altimeter ice thickness 1996
• Altimeter estimates exclude thin (<1m) and open water or approximately 6% of the ice cover during winter.
Seymour Laxon2nd Envisat Summer School
Arctic Mean Winter Sea Ice Thickness
Bourke and McLaren, JGR, 1992
Seymour Laxon2nd Envisat Summer School
ERS Radar Altimeter Sea Ice Thickness93 94 95 96 97 98 99
OCT
NOV
DEC
JAN
FEB
MAR
Metres
Seymour Laxon2nd Envisat Summer School
Thickness trends and variabilitySea Ice Trends 1993 - 1999
Holloway , J. Clim, 2001.
Seymour Laxon2nd Envisat Summer School
Thickness trends and variabilitySea Ice Trends 1993 - 1999 Winter Ice Thickness anomalies 1993 - 2001
Seymour Laxon2nd Envisat Summer School
Thickness trends and variabilityWinter Ice Thickness anomalies 1993 - 2001
Beaufort SeaIce ThicknessWinter 95/96 -Winter 97/98
+ 0.5m
Seymour Laxon2nd Envisat Summer School
Thickness trends and variabilityWinter Ice Thickness anomalies 1993 - 2001
Beaufort SeaIce ThicknessWinter 97/98 -Winter 00/01
-1.5m
Seymour Laxon2nd Envisat Summer School
Anomalies in Winter Ice Thickness
• 1993 - 2001 Inter-annual variability of ice thickness 8%• 1993 - 2001 Inter-annual variability in ice extent 1.7%
Seymour Laxon2nd Envisat Summer School
Control of Ice thickness Change ?
Ice Thickness Change
Seymour Laxon2nd Envisat Summer School
Control of Ice thickness Change - Arctic Oscillation
Ice Thickness ChangeWind Circulation(Dynamics)
Seymour Laxon2nd Envisat Summer School
Control of Ice thickness Change - Arctic Ocean Oscillation
Ice Thickness ChangeOcean Circulation(Dynamics)
Seymour Laxon2nd Envisat Summer School
Ice Thickness Change
Control of Ice thickness Change - Summer Melt?
Ice Thickness ChangeSummer Melt(thermodynamics)
R2 = 0.924
Seymour Laxon2nd Envisat Summer School
Sea Ice Thickness Change Melt Season Length
[Smith, 1998, GRL]
[Laxon, et. al , 2003 Nature]
Arctic Ice Thickness from ERS altimetry
Seymour Laxon2nd Envisat Summer School
AVHHR Arctic Temperature Anomalies
+0.09 -0.30 +0.33
-0.02 -0.43 -0.20
ThicknessChange
Comiso, JGR 2003
Seymour Laxon2nd Envisat Summer School
Record sea ice retreat Summer 2002
Seymour Laxon2nd Envisat Summer School
Arctic sea ice thickness time-series
Seymour Laxon2nd Envisat Summer School
Arctic sea ice thickness time-series
Winter01/02
Seymour Laxon2nd Envisat Summer School
Observed and model anomalies in ice thickness during the 1990’s (NERC Thematic COAPEC)
[Laxon, et al., Nature 2003]
CPOMModel
Seymour Laxon2nd Envisat Summer School
Changes in thickness East Vs West
Seymour Laxon2nd Envisat Summer School
Seymour Laxon2nd Envisat Summer School
∂gdt
= −∂( fg)
∂h− div(Ug) + ψ + φ
RA(-2)
(A)ATSR
(A)SAR
Potential Contribution of ERS/ENVISAT
Seymour Laxon2nd Envisat Summer School
CryoSat
Seymour Laxon2nd Envisat Summer School
Arctic Ocean Observing System
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