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)
• GSL Recontructions (Church et al)
• Unresolved Vertical Land Motion - main uncertainty

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

Woodworth (1999)
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Tide Gauge and Geological Records Nova Scotia
Reconstruction (black circles) Halifax tide gauge
(open circles)
Gehrels et al. (2005)
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PSMSL Database
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Church and White (2006)
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Interdecadal Variability
San Diego
San Francisco
Honolulu
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San Franciso
Honolulu
Firing et al., 2004
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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

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Douglas - GIA (Peltier, 2001)
Average 1.840.35 mm/yr
Record lengths 72-97 years
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Holgate and Woodworth (2004)
Average of overlapping decadal trends within each
region after subtracting long-term trend. 177
stations from 14 regions.
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Average decadal trends, Overall average 1.7
mm/yr
Estimated GSL change 1948-2002
Holgate and Woodworth (2004)
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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

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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)

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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

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Trend of Sea Level Difference, Tide Gauge - T/P,
Jason
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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)
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Church and White (2006)
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Land Motion and Sea Level Trends at Hawaii
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Steric Trends, World Ocean Atlas
Caccamise et al. (2004)
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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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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
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GSL change 1948-2002
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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
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TOPEX/Poseidon SSH Trends