Breer i Arktis og globale havnivåendringer Jon Ove Hagen Institutt for geofag Universitetet i Oslo
Bresmelting Svalbard 1928 2002 (from NP and Greenpeace) Blomstrandbreen, Svalbard
Typisk Svalbard bre: Lovénbreen Photo: Jack Kohler, NP
UNIVERSITY OF OSLO Impacts from glaciers on local and global sea level l Isostatic effects local - ice load - shrinking uplift/rebound l Fresh water flux mass balance/volume changes of land-based ice masses - direct effect on global mean sea level
UNIVERSITY OF OSLO Hva påvirker havnivået? l Termisk ekspansjon av havvannet l Landbaserte ismassers volumendring l Antarktis l Grønland l Lokale breer og iskapper l 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
70 60 50 40 30 20 10 0 m Volume sea level (m) Glaciers and Ice caps (0,5 m) Greenland (7,2 m) Antarctica (61,1 m)
Globale ismasser - havnivåpotensialet Glaciers Ice caps Greenland Antarctica Number >160 000 70 Area 10 6 km 2 0,43 0,24 1,71 12,37 Volume (10 6 km 3 ) 0,08 0,1 2,85 25,71 Volume sea level (m) 0,24 0,27 7,2 61,1
Volume (%) 100% = 28.4 M km 3 Glaciers 0.5 Greenland 10.5 Accumulation (%) 100% = 3083 Gt a -1 Glaciers 22.4 Current Sea Level Rise (%) 100% = 0.8 mm a -1 Antarctica 10 Greenland 20 Antarctica 61.1 Greenland 16.5 Glaciers 70 Antarctica 89.1
Bredekte områder utenom Grønland og Antarktis From Gregory et al. (2001)
Relativ avrenning (%) fra breene utenom innlandsisene
Norges breer Areal ca. 2600 km 2 (A<1% av Norges areal) Volum ca. 180 km 3 Antall ca. 1600 Havnivåpotensialet ca. 0,4 mm Svalbard: Areal Volum ca. 6000 km 3 Havnivåpotensialet ca. 10 mm ca. 36 600 km 2 - (15 x Skandinavia)
Mass balance V/ a = M a - M m - M c ± M b Where Ma = accumulation, Mm = melting, Mc = calving and Mb = bottom melt/freeze Volume change is derived from altitude spot change h 1 [ h] DEM 1 DEM n = V : h t s = b + w u gradh s s = A DEM 1 δ V δh/ δt
Glacier mass balance sites in the Arctic B n = V/ V/ a = M a - M m A measured < 0.1 % of all
UNIVERSITY OF OSLO Svalbard - Austre Brøggerbreen 1967 2002 bn mean 1967 2002: 0.45 m w.eq. (from J. Kohler, NP) 1,5 1,0 0,5 0,0-0,5-1,0-1,5-2,0 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 General slightly negative but no increasing melt-trend trends from 1950ies to about 1990 Since late 1980ies/early 1990ies increased melting trend l Alaska: increasing melt rate: mid 50ies mid 1990ies ~ - 0.52 m/y mid 1990ies present ~ - 1,8 m/y l Canada: stable or slightly negative 1960 end 1980ies then increased melt rate l Svalbard: slightly negative since 1960ies end 1990ies - recent trend towards more melting after 2000 l Russian Arctic - slightly negative no annual mass balance data
Global cumulative net balance
Observationally based global estimate of mass balance period mm SLE a -1 1960-1992 + 0.35 ± 0.26 1992-2003 + 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 Record melt extent in 2005 (Huff & Steffen, 2005)
Calving V/ V/ a = M a - M m - M c ± M b l Arctic glaciers/ice caps: 10 % to 50% of the ablation l Greenland: 40% to 60% of the total ablation l Ca. 90% of the mass loss from the Antarctic ice sheet l still calving is the term of the mass balance budget with the largest uncertainty
Calving from ice shelves
Svalbard
The Greenland Ice Sheet accelerates Velocity (m/yr) (Rignot & Kanagaratnam, 2006) Courtesy: Steve Morgan/Greenpeace Ice sheet mass loss (km3/yr) 300 200 100 0 1996 2000 2005 Year AD 0.8 0.6 0.4 0.2 0 Sea level rise (mm/yr)
Processes that increase the ice flux l Increased sliding caused by more meltwater l Increased sliding caused by less back-pressure (iceshelf collaps and retreat)
Increased basal sliding l Zwally et al. (2002) has observed increased sliding in summertime, which correlates with surface melting Krabill et al. 2000
UNIVERSITY OF OSLO Feedback effect of surface melting on ice streams Ice velocities and calving rates tend to increase when more water is supplied to a glaciers' drainage system (e.g. Zwally et al., 2002). more surface melting increased sliding and calving surface lowering more surface melting
UNIVERSITY OF OSLO Increased sliding caused by less back-pressure l Larsen Ice shelf retreat triggered speed up of 6-8 times on glaciers upstream of the ice shelf (Scambos et al. 2003) l Jacobshavnbreen, Greenland shrinking retreating ice front doubling of speed (Thomas et al. 2002)
Larsen Ice Shelf collapse Landsat TM, 01-03-86 MODIS Terra, 28-02-2005 Surging of upstream ice streams?
Potential sea level changes until year 2100 - modified from recent trends?
UNIVERSITY OF OSLO l Study the current mass budget of selected target glaciers - the surface mass balance and the calving flux l Study subglacial processes; sliding/hydrology l Study the calving processes l Include the dynamics in modeling of future response l Predict future changes IPY GLACIODYN The dynamic response of Arctic glaciers to climate changes
UNIVERSITY OF OSLO IPY GLACIODYN Target glaciers
Svalbard - 1000 km calving front - many dynamic instable (surge-type)
Svalbard UNIVERSITY OF OSLO
Arctic Climate Impact Assessment The Arctic climate is now warming rapidly and much larger changes are projected Arctic Council International Arctic Science Committee
UNIVERSITY OF OSLO Glacier mass balance modeling (ACIA, 2005) l Static approach l Surface mass balance (M a - M m ) energy balance modeling l Constant geometry l Constant iceberg calving
Modeling the future response V/ a = M a - M m - M c ± M b Net balance changes ( B = M a M m ) B = 12 k = 1 [ C ( T T ) + C ( P P ) ] T, k k ref, k P, k 1 k ref, k Seasonal (monthly) sensitivity C T, k = δ B δ T k ( P P ) C P, k = δ B δ k ref, k l l Modellene avhenger helt av scenariene Store regionale variasjoner
Globale og Arktiske temperatur-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)
Selected glaciers: FraSimultaneous satellitter ground-based airborne and satellite data Fra fly På breen Veien videre : 1. Utvalgte feltmålinger 2.Fjernmåling 3.Modellering