1. Center for Satellite Applications and Research (STAR) Review 09 – 11 March 2010 Image: MODIS Land Group, NASA GSFC March 2000 Closing the Global Sea Level Rise Budget with GRACE, Argo, and Altimetry Observations Presented by Eric Leuliette Presented by Eric Leuliette

2. Center for Satellite Applications and Research (STAR) Review 09 – 11 March 2010 2 Requirement, Science, and Benefit Requirement/Objective Research area: Improve skill of climate predictions and projections and increase range of applicability for management and policy decisions Priority research activity: Develop a capability to make sea level projections on decadal to centennial timescales Science Can the observational sea level rise budget be closed? Benefit Societal benefits: Improved long-term planning for coastal communities affected by sea-level rise Intergovernmental Panel on Climate Change –Sea level: validating simulations and constraining predictions –Global heat budget: fails to be closed; eliminating ocean heat content as source of error is useful to other observing systems (e.g. outgoing radiation) and for climate science and prediction

3. Center for Satellite Applications and Research (STAR) Review 09 – 11 March 2010 3 Challenges and Path Forward Science challenges –Maintaining and improving the sea level CDR Cal/val of operational altimetry missions (Jason-2 and Jason-3) –Resolving the question of whether current trend in sea level reflects a true, long-term acceleration. –Argo instrument biases and sampling issues –Variations in glacial isostatic adjustment models –GRACE lifetime and schedule of follow-on mission Next steps –Basin/regional analyses and impact of Greenland ice melt –Extending time series to the entire altimetry era to understand evolution of sea level contributions Transition Path –NOAA-wide initiative with GFDL to improve the predictions of sea level rise Working group includes Univ. of Hawaii and Univ.of Maryland SLR budget results to evaluate retrospective model simulations of SLR –Contribute to the next IPCC report (E. Leuliette contributing author to 4th Assessment Report; to be nominated to 5th report)

4. Center for Satellite Applications and Research (STAR) Review 09 – 11 March 2010 Sea level budget The equation for the sea level budget may be expressed as SL total = SL steric + SL mass SL total is total sea level Altimeters: Jason-1, Jason-2, and Envisat SL steric is the steric component of sea level Argo (for the upper layer) SL mass is the ocean mass component GRACE + geocenter + oblateness All fields are processed at STAR. 4

5. Center for Satellite Applications and Research (STAR) Review 09 – 11 March 2010 A problem closing the budget? 5 Willis et al. [2008] failed to close the sea level rise budget using a combination of Argo, GRACE, and Jason-1 data Willis et al. [2008]Trend 2003.5–2007.5 Steric sea level–0.5 ± 0.5 mm/year Ocean mass from GRACE+0.8 ± 0.8 mm/year Total sea level, steric + mass+0.3 ± 0.6 mm/year Total sea level, Jason-1+3.6 ± 0.8 mm/year Total sea level Black line: Jason-1 Grey line: Argo+GRACE Suggested possible systematic errors in the observing systems. Willis et al. [2008]

6. Center for Satellite Applications and Research (STAR) Review 09 – 11 March 2010 6 Total sea level from altimetry STAR supports the development of the Radar Altimeter Database System (RADS) –World’s leading platform for sea level climate data records (CDRs) Includes latest correction products Supports STAR’s Cal/Val activities – Intermission – Tide gauge Sea level rise research – Leuliette and Miller [2009]

7. Center for Satellite Applications and Research (STAR) Review 09 – 11 March 2010 Building a climate data record 7 Calibration is critical for CDRs. STAR supports Mitchum (USF) in calibrating altimeters with a global tide gauge network. STAR contributes to the Ocean Surface Topography Science Team cal/val efforts. Jason-1 and Jason-2 special issues Leuliette et al. 2004 Leuliette et al. 2010

8. Center for Satellite Applications and Research (STAR) Review 09 – 11 March 2010 Steric sea level analysis 8 STAR produced monthly fields of steric sea level variations using a method that removed WOCE climatology before interpolation The budget analysis in Leuliette and Miller [2009] excluded 2003 because of poor coverage of the Southern Hemisphere. Trends in steric sea level 2004 – 2008

9. Center for Satellite Applications and Research (STAR) Review 09 – 11 March 2010 STAR GRACE processing STAR processes GRACE gravity fields into ocean mass variations – Ocean mass variations observed directly from GRACE have little trend for 2004–2009. A complete analysis must account for ocean mass changes “masked” by geoid variations from the solid Earth’s response to ice melt since the last ice age (Glacial Isostatic Adjustment, GIA) – Uncertainty in ice sheet history, 20% (?) – Published results differ more than forcing uncertainty 9 Peltier (2004,2009)Unpublished (Proudman)

10. Center for Satellite Applications and Research (STAR) Review 09 – 11 March 2010 GIA corrections Uncertainties in the GIA correction is the largest source of error in the observation sea level rise budget –GIA models agree that accounting for GIA changes in altimetry observations adds +0.3 to +0.5 mm/year to global sea level rise. The disagreement is amplified for global ocean mass. -Paulson et al. (2007): +1.0 mm/year -Peltier (2004, 2009): +1.9 mm/year STAR is collaborating with solid earth geophysicists to improve GIA models –Horton (University of Pennsylvania) –Tamisiea (Proudman Oceanographic Institute) 10

11. Center for Satellite Applications and Research (STAR) Review 09 – 11 March 2010 Closing the budget 11 Results of Leuliette and Miller [2009] Blue lines: Direct observations Red lines: Inferred from budget equation SL total = SL steric + SL mass

12. Center for Satellite Applications and Research (STAR) Review 09 – 11 March 2010 With our analysis, we can close the sea level rise budget for the period of 2004 to 2009.25. Demonstrates that the three observation systems can be used for cross- calibration. Conclusion: Closing the budget Sea level components 90% confidence intervals Trend (mm/year) Steric sea level (Argo)0.5 ± 0.5 Ocean mass (GRACE and Paulson GIA)0.9 ± 0.3 Ocean mass (GRACE and Peltier GIA)1.8 ± 0.3 Total sea level: steric + mass (Paulson GIA)1.4 ± 0.6 Total sea level: steric + mass (Peltier GIA)2.3 ± 0.6 Total sea level from Jason-1/21.8 ± 1.1 12

13. Center for Satellite Applications and Research (STAR) Review 09 – 11 March 2010 13 Challenges and Path Forward Science challenges –Maintaining and improving the sea level CDR Cal/val of operational altimetry missions (Jason-2 and Jason-3) –Resolving the question of whether current trend in sea level reflects a true, long-term acceleration. –Argo instrument biases and sampling issues –Variations in glacial isostatic adjustment models –GRACE lifetime and schedule of follow-on mission Next steps –Basin/regional analyses and impact of Greenland ice melt –Extending time series to the entire altimetry era to understand evolution of sea level contributions Transition Path –NOAA-wide initiative with GFDL to improve the predictions of sea level rise Working group includes Univ. of Hawaii and Univ.of Maryland SLR budget results to evaluate retrospective model simulations of SLR –Contribute to the next IPCC report (E. Leuliette contributing author to 4th Assessment Report; to be nominated to 5th report)