Rate of mass
increase (billion tonnes/year)
100
4
0
8
1
-100 5
2
12
3
6
10
7
-200
11
9
-300
1992 1996 2000 2004
Jakobshavn
Observation period
Kangerdlugssuaq
Surface-elevation change (cm/year)
Helheim
-50 -25 0 25 50
Figure 6A.5: Greenland, showing rates of surface-elevation change between the late 1990s and 2003, derived by
comparing satellite and aircraft laser-altimeter surveys. The graph shows rates at which the ice-sheet mass was es-
timated to be changing based on satellite radar-altimeter surveys (black), airborne laser-altimeter surveys (green),
airborne/satellite laser-altimeter surveys (purple), mass-budget calculations (red), temporal changes in gravity
(blue). Rectangles depict the time periods of observations (horizontal) and the upper and lower estimates of mass
balance (vertical). Jakobshavn, Helheim, and Kangerdlugssuaq are fast glaciers that doubled in speed recently.
Sources (corresponding to numbers on rectangles): 1 and 2 Krabill and others 2000
20
and 2004
21
; 3 Thomas and others 2006
27
; 4 Zwally
and others 2005
8
; 5 to 7 Rignot and Kanagaratnam 2006
22
; 8 and 9 Velicogna and Wahr 2005
23
and 2006A
24
; 11 Chen and others
2006A
25
; 10 Ramillien and others 2006
5
; 12 Luthke and others 2006
26
108 GLOBAL OUTLOOK FOR ICE AND SNOW