Estimates of Global Sea Level Change from Tide Gauges Sampling Issues 20th Century Global Sea Level...
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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
Tide Gauge and Geological Records: Nova Scotia
Gehrels et al. (2005)
Reconstruction (black circles)Halifax tide gauge (open circles)
Estimate GSL Change as the average of linear trends from
selected tide gauges
• Requires long records (> 60 years) at “stable” sites resulting in poor spatial coverage, few degrees of freedom
• Ground motion correction specified using Global Isostatic Adjustment (GIA) models
Average of overlapping decadal trends within each region after subtracting long-term trend. 177 stations from 14 regions.
Holgate and Woodworth (2004)
Average decadal trends, Overall average = 1.7 mm/yr
Estimated GSL change 1948-2002
Holgate and Woodworth (2004)
GSL ReconstructionChambers 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
Church and White (2006)
1870-1935: 0.71±0.40 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)
Remains an average of tide gauge records and the number of stations is a concern prior to 1950
Trend primarilyfrom EOF 0
Redistribution modes non-stationary
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)
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
GPS VelocitiesHilo-Honolulu Differential
Sea Level* 1.9 ± 0.9 mm/yr
GPS -0.4 ± 0.4 mm/yr95% 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
Trend Changes 1945-2002Trend 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