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

Longest records suggest rate increase in the 1900s relative to the 1800s Woodworth (1999)

Tide Gauge and Geological Records: Nova Scotia Gehrels et al. (2005) Reconstruction (black circles) Halifax tide gauge (open circles)

PSMSL Database

Church and White (2006)

Interdecadal Variability San Francisco San Diego Honolulu

Firing et al., 2004 San Franciso Honolulu

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

Douglas - GIA (Peltier, 2001)Average = 1.84±0.35 mm/yr Record lengths: years

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 Holgate and Woodworth (2004)

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

Church and White (2006) : 0.71±0.40 mm/yr : 1.84 ±0.19 mm/yr : 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 primarily from EOF 0 Redistribution modes non-stationary

Trend of Sea Level Difference, Tide Gauge - T/P, Jason

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)

Church and White (2006)

Land Motion and Sea Level Trends at Hawaii

Caccamise et al. (2004) Steric Trends, World Ocean Atlas

Summary Different analyses of RLR dataset yield consistent 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 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

GSL change

Trend Changes Computation of the average rate of relative sea level rise from time t 0 to Dec. 2002, for various starting times t 0, as well as the associated 95% confidence interval

TOPEX/Poseidon SSH Trends