Sea Level Rise: An Interdisciplinary Science and Societal Problem

1. Determination and Quantificationof the 20th Century Sea Level RiseChung-Yen Kuo, C.K. Shum, Yuchan YiDivision of Geodetic Science, School of Earth SciencesThe Ohio State University15 Years of Progress in Radar AltimetryVenice, Italy13–18 March 2006

2. Sea Level Rise: An Interdisciplinary Science and Societal Problem • By 2020, over 60% of world’s population would live near coastal regions • Human or anthropogenic effect is believed to have resulted in increased concentrations of greenhouse gas (e.g., CO2), causing warming of the Earth (IPCC 2001) • Global warming causes increased melting of the ice sheets and glaciers, thus rising the sea level • 20th century sea level rise estimates: ~10-20 cm [IPCC TAR, Church et al., 2001]. Ice sheets: ~0.2 mm/yr; thermal expansion: 0.5 mm/yr; Total: 0.7±0.6 mm/yr Unexplained:0.7 to 1.2 mm/yr Accurately measured sea level rise is a good indicator for one of the consequences of global warming

3. IB correction (ECMWF) applied ±81.50 latitude After “geoid” corrections [Peltier, 2003]: Trend = 2.90 mm/yr, ICE-4G model = 2.98 mm/yr, BIFORST model Uncertainty estimated by extending data span to 19 years, and based on original 8-yr analysis by [Guman et al., 1997]. Potential orbit/ITRF drift errors (~0.3 mm/yr) not included [Ries, 2005]. Error dominated by Interannual or longer Variations.

4. IB correction (ECMWF) applied Estimated Global Sea Level Trend = 2.6 mm/yr (2.8 mm/yr, corrected for geoid change using ICE-4G) Estimated Trend Error Dominated by Interannual or longer Variations

5. 1987-2000 1952-2000 1902-2000 1992-2000 Data Span for “Stable” Sea Level Trend Estimate and Sea Level Acceleration (27 TGs)

6. Data Span for “Stable” Sea Level Trend Estimate and Sea Level Acceleration (651 TGs)

7. Trend [mm/yr] 1993-2003 1955-2003 1985-2003 Data Span for “Stable” Thermosteric Sea Level Trend Estimate and Thermosteric Sea Level Acceleration

8. Sea Level from Multiple Atlimetry & Tide Gauge (1900-2002) ICE-4G Geoid effect on altimetry (±81.5)=0.2 mm/yr ICE-4G Geoid effect on altimetry (around TG)=0.1 mm/yr IB correction (NCEP or ECMWF) applied, 651 tide gauges, ICE-4G nominal GIA model used

9. Normalized sea level change “patterns” due to “self-gravitational” effect of present-day melt water from Antarctica (top), Greenland (middle), and mountain glacier (bottom) ice melt [Mitrovica et al., 2001]: ST =GIA corrected sea level from tide gauges; Sn are maps of sea level variation patterns; VA, VG, VM are sea level due to the 3 ice systems; V0 are other contributions, e.g., thermal expansion

10. Dynamic Topography From WOA-01 0-3000 m 0-1000 m Computed Using NOAA WOA-01 data [Levitus, 2001]

11. Sea Level Determination & Characterization Using Tide Gauges & Multiple Altimetry Observation Equations [Plag & Juttner, 2001; Mitrovica et al. 2002; Kuo et al. 2004]: Where S are normalized spatial functions assumed for oceanic (thermal), Antarctica, Greenland, glacier, and PGR variations in sea leve;, yT and yv are sea level trend and vertical motion respectively Elementwise Weighted Total LS (EW-TLS) [Premoli & Rastello, 2002] : Where y are observations(tide gauge & altimetry);  are estimated scale factors of spatial functions, S

12. Simulation Study for Sea Level Adjustment Perfect solutions are 0.6 mm/yr, 0.3 mm/yr , 0.5 mm/yr, 0.3 mm/yr, and 1.0 respectively.

13. Observed: 0.07 mm/yr Observed: 0.20 mm/yr Antarctic: 0.36±0.16 mm/yr Greenland: 0.59±0.15 mm/yr Observed: 0.4 mm/yr Observed: 0.52 mm/yr Thermosteric: 0.17±0.05 mm/yr Glacier: 0.62±0.10 mm/yr Estimated Global Sea Level Rise Using Selected Tide Gauges (585) & Altimetry (1948–2004)

14. Estimated Global Sea Level Rise Using Tide Gauges and Satellite Altimetry (1948–2003) Estimated Sea Level Rise = 1.74±0.24 mm/yr 585 selected tide gauges, multiple satellite altimetry used

15. Estimated Global Sea Level Rise Using Tide Gauges and Satellite Altimetry (1900–2003) Estimated Sea Level Rise = 1.73±0.21 mm/yr 585 selected tide gauges, multiple satellite altimetry used

16. 20th Century Sea Level Budget • 20th century sea level rise estimates: ~10-20 cm [IPCC, Church et al., 2001].Ice sheets: ~0.2 mm/yr; thermal expansion: 0.5 mm/yr Total: 0.7±0.6 mm/yr Unexplained:0.7 to 1.2 mm/yr • Current: steric (1947-2000): 0.4 mm/yr[Levitus et al., 2005], glaciers (Amundsen, Alaska): 0.52 mm/yr[Ahrendt et al., 2002], ice sheets: 0.45 mm/yr (0.20, 0.07, 0.11, 0.07 mm/yr for Greenland, Antarctica, Patagonia, Canadian)[Krabill et al. 2005, Rignot et al., 2005, Thomas et al. 2005]), hydrological: 0.12 mm/yr [Ngo-duc et al., 2005, Milly et al 2003], anthropogenic: 0.05 mm/yr • Observed trend:1.8±0.5 mm/yr[Douglas, 2001; Church et al., 2004]; 0.9 mm/yr [Plag, 2005], 1.73±0.21 mm/yr[Shum & Kuo, 2005] Total: 1.54 mm/yr Unexplained: ~ –0.64 to +0.26 mm/yr

17. Conclusions • 20th Century global sea level rise is estimated as 1.73±0.21 mm/yr using tide gauges and altimetry with geophysical models • Estimated size and global patterns of various contributions of sea level rise (ice sheets, glacier, thermal expansion, hydrological contribution ignored) do not all agree well with observations, however, the overall budget (observation and model/quantifications) agree much better now than 2001 (IPCC TAR) • Analysis of available tide gauge and thermosteric sea level data indicate that there is no evidence that sea level acceleration occurred in the 1990s