breer i arktis og globale havnivåendringer · norges breer • areal ca. 2600 km 2 (a bre
TRANSCRIPT
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
UNIVERSITYOF OSLO
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
UNIVERSITYOF OSLO
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
UNIVERSITYOF OSLO
Stake net, radar- and GPS-profiles
Ground-based 800 MHz radar and GPS
Limbo on ULS – AWS-1 Eton
UNIVERSITYOF OSLO
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
UNIVERSITYOF OSLO
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).
UNIVERSITYOF OSLO
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
??
UNIVERSITYOF OSLO
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
UNIVERSITYOF OSLO
IPY GLACIODYN Target glaciers
UNIVERSITYOF OSLO
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’
UNIVERSITYOF OSLO
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
??
UNIVERSITYOF OSLO
Greenland ice stream calving
Triggering increased sea level ?
UNIVERSITYOF OSLO
More calving in Svalbard ?