Are the Ice caps melting? - Earth Online - ESA · Are the Ice caps melting? Seymour Laxon Centre for Polar Climate and Modelling, University College London •Greenland •Antarctica

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


Ice Sheet Mass Balance -2


Summer Melting

Wet Snow Zone Wet Snow Zone

Percolation Zone Percolation Zone


Ice Sheet Melt Duration - ERS Scatterometer

Courtesy I. Ashcraft, BYU


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


Ice Sheet Elevation


Ice Sheet Elevation Change



Ice Sheet Flow - SAR Interferometry


Ice Sheet Flow - SAR Interferometry


Ice Sheet Flow

[JPL]


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)


Changes in minimum extent since 1979

QuickTime™ and aYUV420 codec decompressorare needed to see this picture.


Yearly Anomalies of the Perennial

Ice Cover:1979 to 2003

J. Comiso, GRL, 2002


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


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


Trends in the Perennial Ice (1979-2003)and Surface Temperature (1981-2002)

Ref. Comiso, GRL, 2002



QuickTime™ and a decompressor

are needed to see this picture.


Arctic Sea Ice : 40% thinning in just 30 years!


On both sides of the Arctic!


Submarine Trends

Rothrock, et al., 2003, JGR.


Tucker et. al., GRL, 2001

1950

2050

• Significant thinning in the Western Arctic but not at the North Pole


(Winsor, GRL, 2001)

1950

2050


Arctic Ice Thinning - Computer Models


Arctic Ice Thinning - Computer Models

Holloway, et al. , J. Clim., 2001.


Inter-annual Variability of Ice Thickness


Inter-annual Variability of Ice Thickness


Sea Ice Dynamic and ThermodynamicsThermodynamics

Dynamics

Perovich, Ann, Glaciol., 2001.


∂gdt

= −∂( fg)

∂h− div(Ug) + ψ + φ

Dynamic and Thermodynamic control of ice thickness


Courtesy Mark Hopkins

QuickTime™ and a decompressor

are needed to see this picture.

Ice Ridging


Arctic Oscillation (AO)

2050

AO Index 1958-2000AO Index 1958-2000


AO Index 1958-2000


Arctic Ocean Oscillation (AOO)


AOO Index 1946-2000


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


Ice Thickness Simulations (1950 - 2000)

Rothrock, et al., JGR, 2003.


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?


Freeboard

h =ct2

Satellite Altimetry - Measurement Principle


Geosat 1985 -


ERS-1 1991-


ERS altimeter ice thickness 1996

• Altimeter estimates exclude thin (<1m) and open water or approximately 6% of the ice cover during winter.


Arctic Mean Winter Sea Ice Thickness

Bourke and McLaren, JGR, 1992


ERS Radar Altimeter Sea Ice Thickness93 94 95 96 97 98 99

OCT

NOV

DEC

JAN

FEB

MAR

Metres


Thickness trends and variabilitySea Ice Trends 1993 - 1999

Holloway , J. Clim, 2001.


Thickness trends and variabilitySea Ice Trends 1993 - 1999 Winter Ice Thickness anomalies 1993 - 2001


Thickness trends and variabilityWinter Ice Thickness anomalies 1993 - 2001

Beaufort SeaIce ThicknessWinter 95/96 -Winter 97/98

+ 0.5m


Thickness trends and variabilityWinter Ice Thickness anomalies 1993 - 2001

Beaufort SeaIce ThicknessWinter 97/98 -Winter 00/01

-1.5m


Anomalies in Winter Ice Thickness

• 1993 - 2001 Inter-annual variability of ice thickness 8%• 1993 - 2001 Inter-annual variability in ice extent 1.7%


Control of Ice thickness Change ?

Ice Thickness Change


Control of Ice thickness Change - Arctic Oscillation

Ice Thickness ChangeWind Circulation(Dynamics)


Control of Ice thickness Change - Arctic Ocean Oscillation

Ice Thickness ChangeOcean Circulation(Dynamics)


Ice Thickness Change

Control of Ice thickness Change - Summer Melt?

Ice Thickness ChangeSummer Melt(thermodynamics)

R2 = 0.924


Sea Ice Thickness Change Melt Season Length

[Smith, 1998, GRL]

[Laxon, et. al , 2003 Nature]

Arctic Ice Thickness from ERS altimetry


AVHHR Arctic Temperature Anomalies

+0.09 -0.30 +0.33

-0.02 -0.43 -0.20

ThicknessChange

Comiso, JGR 2003


Record sea ice retreat Summer 2002


Arctic sea ice thickness time-series


Arctic sea ice thickness time-series

Winter01/02


Observed and model anomalies in ice thickness during the 1990’s (NERC Thematic COAPEC)

[Laxon, et al., Nature 2003]

CPOMModel


Changes in thickness East Vs West



∂gdt

= −∂( fg)

∂h− div(Ug) + ψ + φ

RA(-2)

(A)ATSR

(A)SAR

Potential Contribution of ERS/ENVISAT


CryoSat


Arctic Ocean Observing System

Documents

Are the Ice caps melting? - Earth Online - ESA · Are the Ice caps melting? Seymour Laxon Centre for Polar Climate and Modelling, University College London •Greenland •Antarctica