1. Toward closing the globally averaged sea level budget on seasonal to interannual time scales Josh K. Willis joshua.k.willis@jpl.nasa.gov Jet Propulsion Laboratory Don P. Chambers, R. Steven Nerem Co-Authors:

2. Outline Motivation for assessing components of sea level rise Motivation for assessing components of sea level rise Assessing the recent sea level budget Assessing the recent sea level budget Remaining discrepancies Remaining discrepancies The spurious cooling signal The spurious cooling signal

3. Motivation

4. How fast will sea level rise? [Rahmstorf et al., 2007] Tide Gauge Observations Satellite Observations Climate Model Predictions (IPCC 3rd Assessment, 2001)

5. The Seasonal to Interannual Sea Level Budget from 2003 to 2007

6. What causes globally-averaged sea level rise? addition of freshwater addition of heat + = Total sea level rise Argo JasonGRACE (roughly)

7. Argo Argo data only Argo data only All data with known pressures errors removed. All data with known pressures errors removed. Steric height computed from Argo Temp. & Sal. Steric height computed from Argo Temp. & Sal. Monthly objective maps of large scale steric variability. Monthly objective maps of large scale steric variability.

8. Argo data distribution Mid 2003 is data sparse in Southern Hemisphere 1800 km zonal, 700 km meridional e-folding scale

9. Test of Mapping Procedure RMS difference: 1.6 mm Jason data interpolated to time and location of Argo profiles Jason data interpolated to time and location of Argo profiles Mapped using same mapping procedures Mapped using same mapping procedures Compared with full Jason time series Compared with full Jason time series

10. Atmospheric and Ocean models Atmospheric and Ocean models Adjustment for incompressibility Adjustment for incompressibility Degree 2, order 0 coefficients from SLR Degree 2, order 0 coefficients from SLR Monthly model of geocenter + Monthly model of geocenter + GIA correction * GIA correction * Land mask Land mask ± 66° latitude ± 66° latitude + Swenson et al., JGR-Oceans, submitted. * Paulson et al., Geophys. J. Int., 2007 ± ± 0.2 mm/yr

11. Mass exchange with high latitudes Difference between ± 66° total ocean average and ± 66° average Very small interannual signal

12. Jason Jason data only Jason data only Standard corrections applied (including IB) Standard corrections applied (including IB) GIA +0.3 mm/yr [Douglas and Peltier, 2002] GIA +0.3 mm/yr [Douglas and Peltier, 2002]

13. The recent sea level budget Global Mean Sea LevelGlobal MSL, no seasonal Total (Jason) Steric (Argo) Mass (GRACE) Total (Jason) Steric (Argo) Mass (GRACE)

14. Remaining Discrepancies in the Sea Level Budget

15. Sea Level Budget AmplitudePhaseslope Steric3.7 ± 0.8 mm104° ± 13°-0.5 ± 0.5 mm/yr Mass6.8 ± 0.6 mm261° ± 5°0.8 ± 0.8 mm/yr Sum3.7 ± 1.0 mm239° ± 16°0.3 ± 0.9 mm/yr Altimeter3.2 ± 1.3 mm250° ± 23°3.6 ± 0.8 mm/yr Seasonal cycles agree to within random error 4-year trends have discrepancy larger than random error => systematic error remains!

16. The recent sea level budget Global MSL, no seasonal cycle, no trend RMS difference: 1.6 mm Total (Jason) Steric (Argo) Mass (GRACE) Removal of trend brings all three estimates into excellent agreement

17. The recent sea level budget 4-year Trends in sea level Jason Jason-GRACE Argo General agreement is encouraging But, difference in S. Hemisphere trends is concerning

18. the Spurious Cooling Signal the Spurious Cooling Signal

19. The “rapid cooling” signal Adapted from Lyman et al. (GRL, 2006) ~ 6 mm drop in thermosteric sea level Most of the cooling was caused by two in situ data biases

20. 3.4 mm/year 1.3 mm/year

21. Conclusions Seasonal, intra- and interannual variations in sea level can be explained as sum of steric and mass components Seasonal, intra- and interannual variations in sea level can be explained as sum of steric and mass components Large discrepancy remains in 4-year trend Large discrepancy remains in 4-year trend Rapid Ocean cooling was spurious Rapid Ocean cooling was spurious Global ocean observing systems are improving, but they are not yet complete! Global ocean observing systems are improving, but they are not yet complete!

22. References Willis, J. K., D. P. Chambers, and R. S. Nerem, “Closing the Globally Averaged Sea Level Budget on Seasonal to Interannual Time Scales,” J. Geophys. Res., submitted. Lyman, J. M., J. K. Willis, and G. C. Johnson, 2006: Recent cooling of the upper ocean. Geophysical Research Letters, 33, L18604, doi:10.1029/2006GL027033. Willis, J. K., Lyman, J. M., G. C. Johnson, and J. Gilson (2007a), Correction to “Recent cooling in the upper ocean”, 34, L16601, doi:10.1029/2007GL030323.. Willis, J. K., Lyman, J. M., G. C. Johnson, and J. Gilson (2007b), In Situ Data Biases and Recent Ocean Heat Content Variability, J. of Atmos. Oceanic Technol., submitted, October, 2007. Wijffels, S., J. K. Willis, C. Domingues, P. Barker, N. White, A. Gronell, K. Ridgway, and J. Church, “Changing eXpendable Bathythermograph Fall-rates and their Impact on Estimates of Thermosteric Sea Level Rise,” J. Atmos. Oceanic Technol., in press. Paulson, A., S. Zhong, and J. Wahr, Inference of mantle viscosity from GRACE and relative sea level data, Geophys. J. Int. (in press), 2007. Swenson, S. C., D. P. Chambers, and J. Wahr (2007), Estimating geocenter variations from a combination of GRACE and ocean model output, J. Geophys. Res.. submitted.