Breer i Arktis og globale havnivåendringer

Jon Ove Hagen Institutt for geofagUniversitetet i Oslo

Bresmelting – Svalbard 1928 – 2002(from NP and Greenpeace)

Blomstrandbreen, Svalbard

Typisk Svalbard bre:

Lovénbreen

Photo: Jack Kohler, NP

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Impacts from glaciers on local and global sea level

Isostatic effects – local - ice load - shrinking uplift/rebound

Fresh water flux – mass balance/volume changes of land-based ice masses

- direct effect on global mean sea level

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Hva påvirker havnivået ?

Termisk ekspansjon av havvannetLandbaserte ismassers volumendring

Antarktis Grønland Lokale breer og iskapper

Grunnvann, permafrost, kunstig vannmagasinering

Globale havnivåendinger siste 140 000 år

Grønlands middeltemperatur siste 100 000 år

Global sea level changes last 18 000 years (since LGM)

12000-6000 BP ~10mm/y

AD 1900-2000 ~ 1.5 mm/y

Gjennomsnittlig globalt hanivå er beregnet til å stige 0.09 til 0.88 m innen 2100 (IPCC, 2001)

(men med store regionale variasjoner !)

Potensielle havnivåendringer fram til år 2100 (IPCC, 2001)

Kurvene

Volume sea level (m)

010203040506070

Glaciers and Icecaps (0,5 m)

Greenland (7,2 m) Antarctica (61,1 m)

m

Globale ismasser - havnivåpotensialet

Glaciers Ice caps Greenland Antarctica

Number >160 000 70

Area 106 km2

0,43 0,24 1,71 12,37

Volume (106

km3)0,08 0,1 2,85 25,71

Volume sea level (m)

0,24 0,27 7,2 61,1

Norges breer• Areal ca. 2600 km2 (Abre<1% av Norges areal)• Volum ca. 180 km3

• Antall ca. 1600

• Havnivåpotensialet ca. 0,4 mm

• Svalbard: Abre~ 60 %• Areal ca. 36 600 km2 - (15 x Skandinavia)

Volum ca. 6000 km3

• Havnivåpotensialet ca. 10 mm

Comparison of total volume (left), total annual accumulation (middle), and total contribution to sea-level rise (right) for small glacier/ice caps and the ice sheets in Greenland and Antarctica

Glaciers0.5 Greenland

10.5

Antarctica89.1

Volume (%)100% = 28.4 M km3

Glaciers70

Greenland20

Antarctica10

Current Sea Level Rise (%)100% = 0.8 mm a-1

Glaciers22.4

Greenland16.5

Antarctica61.1

Accumulation (%)100% = 3083 Gt a-1

Cryospheric SLR

Bredekte områder utenom Grønland og Antarktis

From Gregory et al. (2001)

Relativ avrenning (%) fra breene utenom innlandsisene

Mass balance

→→

⋅−+= gradhuwbth

sss∂∂

Volume change is derived from altitude spot change h1 →DEM1 [Δh] DEM1 – DEMn = Δ V :

∂V/∂a = Ma - Mm - Mc ± Mb

Where Ma = accumulation, Mm = melting, Mc = calving and Mb = bottom melt/freeze

∫=A

thV δδδ /⇒

Selected glaciers: Simultaneous –ground-based – airborne and

satellite data

Fra satellitter

Fra fly

På breenHvordan måles massebalansen

1. Utvalgte feltmålinger 2.Fjernmåling 3.Modellering

Glacier mass balance sites in the Arctic

Bn = ∂V/∂a = Ma - Mm

A measured < 0.1 % of all

AWS on Austfonna - Riming is a problem

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Stake net, radar- and GPS-profiles

Ground-based 800 MHz radar and GPS

Limbo on ULS – AWS-1 Eton

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Svalbard - Austre Brøggerbreen 1967 – 2002bn mean 1967 – 2002: – 0.45 m w.eq.

(from J. Kohler, NP)

-2,0

-1,5

-1,0

-0,5

0,0

0,5

1,0

1,5

1965 1970 1975 1980 1985 1990 1995 2000

Winter Summer Net

Arctic cumulative volume change(from ACIA, 2005)

Arctic glaciers ~ 50 % of glaciers and ice caps outside Greenland and Antarctica

Alaska: increasing melt rate: mid 50ies–mid 1990ies ~ - 0.52 m/y mid 1990ies – present ~ - 1,8 m/y

Canada: stable or slightly negative 1960–end 1980ies – then increased melt rate

Svalbard: slightly negative since 1960ies – end 1990ies - recent trend towards more melting after 2000

Russian Arctic - slightly negative – no annual mass balance data

General slightly negative but no increasing melt-trend trends from 1950ies to about 1990

Since late 1980ies/early 1990ies increased melting trend

Global cumulative net balance

Annual and cumulative sea level equivalents from glaciers and ice caps (Dyurgerov and Meier, 2005)

Observationally based global estimate of mass balance

period mm SLE a-1

1960-1992 + 0.35 ± 0.261992-2003 + 0.81 ± 0.42

Consensus estimate based on Ohmura (2004), Cogley(2005),Dyurgerov and Meier (2005) (compiled from Raper 2006)

The above includes glaciers and ice caps in Greenland and Antarctica

NB- Large uncertainty of up to ca. ± 70 %

Greenland - peripheral thinning - interior thickening 1994-2000

(from Krabill et al 2000)

NASA airborne laser altimetry

Grønland – smelteområder(ACIA, 2005)

Increasing melt extent on the Greenland Ice Sheet

(Huff & Steffen, 2005)

Record melt extent in 2005

Calving

∂V/∂a = Ma - Mm - Mc ± Mb

Arctic glaciers/ice caps: 10 % to 50% of the ablation

Greenland: 40% to 60% of the total ablation

Ca. 90% of the mass loss from the Antarctic ice sheet

still calving is the term of the mass balance budget with the largest uncertainty

Calving from ice shelves

Svalbard

Fjellgruppa oktober 06

Austfonna

(Rignot & Kanagaratnam, 2006)

The Greenland Ice Sheet accelerates

Velo

city

(m/y

r)

Courtesy: Steve Morgan/Greenpeace

Processes that increase the ice flux

Increased sliding caused by more meltwater

Increased sliding caused by less back-pressure (ice-shelf collaps and retreat)

(increased accumulation has limited or no effect !)

Increased basal sliding

Zwally et al. (2002) has observed increased sliding in summertime, which correlates with surface melting

Krabill et al. 2000

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Feedback effect of surface melting on ice streams

more surface melting increased sliding and calving

surface lowering more surface melting

Ice velocities and calving rates tend to increase when more water is supplied to a glaciers' drainage system (e.g. Zwally et al., 2002).

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Increased sliding caused by less back-pressure

Larsen Ice shelf retreat triggered speed up of 6-8 times on glaciers upstream of the ice shelf (Scambos et al. 2003)

Jacobshavnbreen, Greenland – shrinking –retreating ice front – doubling of speed (Thomas et al. 2002)

MODIS Terra, 28-02-2005Landsat TM, 01-03-86

Larsen Ice Shelf collapse

Surging of upstream ice streams ?

Greenland mass balance estimates (Thomas et al. 2006)

Potential sea level changes until year 2100- modified from recent trends

??

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Study the current mass budget of selected target glaciers - the surface mass balance and the calving flux Study subglacial processes; sliding/hydrologyStudy the calving processes Include the dynamics in modeling of future responsePredict future changes

IPY – GLACIODYN

The dynamic response of Arctic glaciers to climate changes

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IPY GLACIODYN Target glaciers

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Svalbard

Svalbard - 1000 km calving front- many dynamic instable (surge-type)

Arctic Climate Impact Assessment

International Arctic Science Committee

Arctic Council

’The Arctic climate is now warming rapidly and much larger changes are projected’

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Glacier mass balance modeling(ACIA, 2005)

Static approach Surface mass balance (Ma - Mm)– energy balance modeling

Constant geometry

Constant iceberg calving

( )[ ( ) ]krefkkPk

krefkkT PPCTTCB ,,

12

1,, 1 −+−=Δ ∑

=

kkT TBC δδ=, ( )krefkkP PPBC ,, δδ=

Net balance changes ( ∆B = ∆Ma – ∆Mm)

Seasonal (monthly) sensitivity

Modeling the future response

∂V/∂a = Ma - Mm - Mc ± Mb

Modellene avhenger helt av scenarieneStore regionale variasjoner

Temperatur-anomalier i forhold til 1961-1990

Globale og Arktisketemperatur-scenarier

Modeled global sea-level changes (m) 1990–2100 (IPCC, 2001)

Havnivå-bidrag fra Arktiske

breer(ECHAM-model,

ACIA,2005)

Havnivå bidrag fra Arktiske breer – ulike scenarier (ACIA 2005)

Potential sea level changes until year 2100- modified from recent trends

??

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Greenland ice stream calving

Triggering increased sea level ?

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More calving in Svalbard ?