Why has an acceleration of sea level rise not
been observed
bee
obse ed du
during
g tthe
ea
altimeter
t ete era?
e a
R. S. Nerem, D. P. Chambers, J. Fasullo, M. Merrifield,
G. T. Mitchum, I. Velicogna, and J. Willis
Questions to be Addressed
• How large of an acceleration might we expect to
•
•
•
•
see?
What have we observed during
g the altimeter era?
Could there an error in the altimeter data?
If there has been an acceleration,
acceleration should we have
detected it?
C ld the
Could
th acceleration
l ti off ice
i melt
lt be
b masked
k d by
b a
deceleration in other contributions to sea level
change?
h
?
GRACE
GRACEobserved
mass
changes in
the Arctic
Polar Ice Mass Loss from GRACE
[Velicogna, 2011]
GIA--Corrected J2 Variations
GIA
[Nerem and Wahr, 2011]
Mountain Glaciers: Contribution to Sea Level
25
MSL
L ( mm)
20
1961-1993: 0.5 mm/year
1993-2003: 0.9 mm/year
15
10
5
0
1960
1970
1980
1990
2000
2010
Year
[Dyurgerov and Meier, 2005]
Greenland+Antarctica Sea Level Contributions
14
Quadratic Fit
12
GRACE ((Greenland + Antarctica))
10
ΔM SL (m
mm)
Rate (1993) ~ 0.1 mm/yr
8
Avg
g Rate ((2002-2011)) ~ 1.1 mm/yr
y
Acceleration ~ 0.08 ± 0.02 mm/yr
2
6
4
2
0
1996
2000
Year
2004
2008
2012
Observed GMSL Variations
50
50
40
40
Altimeter GM SL
Quadratic GRE+ANT
ΔM S
SL (mm)
30
30
20
20
Rate = 3.1 mm/year
Acceleration = -0.06 ± 0.04 mm/yr2
10
10
0
Rate = 1.1 mm/year
Acceleration = +0.08 mm/yr2
-10
10
1996
2000
Year
2004
2008
2012
Could there be errors in the altimeter data?
Tide Gauge Calibration
Could there be errors in the altimeter data?
Tide Gauge Calibration
Tide Gauge Corrected JasonJason-2 GMSL
60
Nominal GM SL
w/ Jason-2 TG Correction
40
Acceleration = -0.06 ± 0.04 mm/year
2
ΔM SL (mm
Δ
m)
20
0
Acceleration = -0.045 ± 0.04 mm/year
2
-20
20
-40
1990
1995
2000
Year
2005
2010
2015
The Two Decades of the Altimeter Era
2002-2011
1993-2002
30
60
25
55
Rate = 2.3 mm/year
50
15
45
ΔM
M SL (mm)
Δ M SL (mm)
Rate = 3.5 mm/year
20
10
5
40
35
0
30
-55
25
-10
1994
1996
1998
Year
2000
2002
20
2002
2004
2006
2008
Year
2010
2012
Multivariate ENSO Index (MEI)
[Wolter and Timlin, 1993; 1998]
Histogram of MEI during the Altimeter Era
1993-2002
2002-2011
30
30
Skewness = -0.6
25
25
20
20
Mo
onths
Mo
onths
Skewness = +0.8
15
15
10
10
5
5
0
0
-1
0
1
M EI Value
2
3
-2
-1
0
M EI Value
1
2
Historical Ranking of MEI (1950(1950-present)
YR JAN
1992 60
1993 48
1994 40
1995 55
1996 17
1997 24
1998 61
1999 8
2000 6
2001 23
2002 34
2003 54
2004 39
2005 37
2006 26
2007 51
2008 12
2009 15
2010 53
2011 2
FEB MAR APR MAY JUN JUL AUG
60
60
60
60
59
54
42
54
55
58
58
58
56
54
36
39
45
45
46
50
48
53
52
44
44
41
34
25
21
23
19
24
31
22
20
19
25
48
57
62
62
62
61
61
61
61
55
36
18
9
13
9
12
17
16
12
8
10
18
34
23
23
29
17
20
26
35
28
35
40
30
27
41
53
50
44
52
52
50
39
29
32
33
36
39
28
34
42
35
41
46
48
56
51
51
43
43
38
24
21
16
28
45
46
49
44
34
28
36
18
20
17
5
3
13
17
34
30
22
16
18
25
39
52
52
53
59
58
55
47
16
7
2
2
4
4
19
22
28
16
SEP OCT NOV DEC
42
44
42
44
54
54
47
43
53
57
56
54
23
19
19
21
21
20
29
25
62
61
61
60
14
14
11
13
12
13
14
8
27
22
16
20
28
25
26
32
51
49
51
52
41
42
40
36
43
40
46
45
36
26
22
19
50
47
57
49
10
10
10
9
15
15
18
16
46
53
52
51
1
2
3
4
13
Detrended GMSL versus MEI
3
10
Detrended GM SL
MEI
2
1
0
0
-11
-5
-22
-10
10
1993
-33
1997
2001
2005
Year
2009
ME
EI
Detrended Δ
D
ΔM SL (mm
m)
5
Simulated GMSL Acceleration Recovery
0.2
2
M SL A
Acceleration
n Error (m
mm/yr )
• Determine regression of MEI against
sea level during 1993-present
• Use simulated MEI-based sea level time series from
1900
1900-present
t to
t test
t t recovery off sea llevell acceleration
l ti
0.15
01
0.1
0.05
0
10
20
30
Length of Time Series (Years)
40
50
Updated from Nerem et al. [1999]
Sea Level Contributions
GRACE:
Greenland + Antarctica
Ocean Measurements (Argo)
Thermosteric sea level
Hiatus Periods of Upper Ocean Heat Uptake?
• Ensemble model runs show
evidence of “hiatus decades”
where the ocean above 300
m takes up
p significantly
g
y less
heat than the ocean below
300 m.
• Relatively common climate
phenomenon likely linked to
La Nina conditions.
Meehl et al., 2011, Nature Climate Change, Model-based evidence of
deep-ocean heat uptake during surface-temperature hiatus periods
Spatial Variations in Sea Level Rise 19931993-2011
Western Pacific Sea Level Change
Merrifield (2010)
Summary
• The cryosphere has clearly seen an acceleration of mass loss
•
•
•
during the altimeter era of (0.05 – 0.1 mm/year2 ???).
ENSO-related variability contributes an error to determining the
acceleration of ~0.04 mm/year2
It is likely that a slowdown in thermosteric sea level rise over the
last decade has masked some of the acceleration from the
cryosphere.
h
There is still the possibility of errors in the altimeter data,
especially Jason-2.
Jason 2 Calibrating the altimeter systems to detect such
small accelerations is very difficult.
Total Sea Level and Ocean Mass
Observed Acceleration
50
Rate = 3.1 mm/year
2
Acceleration = -0.06 mm/year
/y
40
ΔM SL (mm)
30
20
10
0
-10
10
1996
2000
2004
Year
2008
2012