Estimates of Global Sea Level Change from Tide Gauges - PowerPoint PPT Presentation

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Estimates of Global Sea Level Change from Tide Gauges

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Estimates of Global Sea Level Change from Tide Gauges Sampling Issues 20th Century Global Sea Level (GSL) Rise Estimates Average of Trends (Douglas et al) – PowerPoint PPT presentation

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Title: Estimates of Global Sea Level Change from Tide Gauges


1
Estimates of Global Sea Level Change from Tide
Gauges
  • Sampling Issues
  • 20th Century Global Sea Level (GSL) Rise
    Estimates
  • Average of Trends (Douglas et al)
  • GSL Recontructions (Church et al)
  • Unresolved Vertical Land Motion - main uncertainty

2
Longest records suggest rate increase in the
1900s relative to the 1800s

Woodworth (1999)
3
Tide Gauge and Geological Records Nova Scotia
Reconstruction (black circles) Halifax tide gauge
(open circles)
Gehrels et al. (2005)
4
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5
PSMSL Database
6
Church and White (2006)
7
Interdecadal Variability
San Diego
San Francisco
Honolulu
8
San Franciso
Honolulu
Firing et al., 2004
9
Estimate GSL Change as the average of linear
trends from selected tide gauges
  • Requires long records (gt 60 years) at stable
    sites resulting in poor spatial coverage, few
    degrees of freedom
  • Ground motion correction specified using Global
    Isostatic Adjustment (GIA) models

10
Douglas - GIA (Peltier, 2001)
Average 1.840.35 mm/yr
Record lengths 72-97 years
11
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12
Holgate and Woodworth (2004)
Average of overlapping decadal trends within each
region after subtracting long-term trend. 177
stations from 14 regions.
13
Average decadal trends, Overall average 1.7
mm/yr
Estimated GSL change 1948-2002
Holgate and Woodworth (2004)
14
GSL Reconstruction
Chambers et al. (2002), Church et al. (2004),
Church and White (2006)
  • Fit T/P EOFs to tide gauge first-differenced
    time series
  • Can include more stations, variable number of
    stations over time
  • Explicit model of redistribution signal, assumes
    T/P modes are representative of past sea level
    variability

15
1870-1935 0.710.40 mm/yr 1936-2001 1.84 0.19
mm/yr 1950-2000 1.75 0.4 mm/yr Consistent
with Douglas et al. (1991,2001), Peltier (2001),
Holgate and Woodworth (2004)
  • Church and White (2006)

16
Trend primarily from EOF 0
Redistribution modes non-stationary
  • Remains an average of tide gauge records and the
    number of stations is a concern prior to 1950

17
Trend of Sea Level Difference, Tide Gauge - T/P,
Jason
18
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20
CGPS Vertical Rates Relative to Regional
Reference Frame
  • Valparaiso, Chile
  • TG - ALT 5.65 mm/yr
  • CGPS -6.4 mm/yr

Foster et al. (2006)
21
Church and White (2006)
22
Land Motion and Sea Level Trends at Hawaii
23
Steric Trends, World Ocean Atlas
Caccamise et al. (2004)
24
Summary
  • Different analyses of RLR dataset yield
    consistent 1.7-1.8 mm/yr GSL rise over last half
    of the 20th century
  • Faster rise rate in 1900s than 1800s in North
    Atlantic records - need for more
    geo-reconstructions in undersampled regions
  • GSL reconstructions highlight interdecadal
    component, possible 20th century acceleration
  • Major uncertainty is unresolved Vertical Land
    Motion, need for direct measurements

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28
GPS Velocities
Hilo-Honolulu Differential Sea Level 1.9 0.9
mm/yr GPS -0.4 0.4 mm/yr 95 Confidence
intervals. entire time series
KOKB -0.2 mm/yr KOK1 -1.2 mm/yr HNLC -1.4
mm/yr MAUI -1.5 mm/yr MKEA -1.8 mm/yr HILO -1.9
mm/yr
29
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30
GSL change 1948-2002
31
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32
Trend Changes 1945-2002
Computation of the average rate of relative sea
level rise from time t0 to Dec. 2002, for various
starting times t0, as well as the associated 95
confidence interval
33
TOPEX/Poseidon SSH Trends
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