Closing the Global Sea Level Rise Budget with GRACE, Argo, and Altimetry Observations

1. Closing the Global Sea Level Rise Budget with GRACE, Argo, and Altimetry Observations Presented by Eric Leuliette

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. 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) 3

4. Sea level budget The equation for the sea level budget may be expressed as SLtotal = SLsteric + SLmass SLtotalis total sea level Altimeters: Jason-1, Jason-2, and Envisat SLstericis the steric component of sea level Argo (for the upper layer) SLmass is the ocean mass component GRACE + geocenter + oblateness All fields are processed at STAR.

5. A problem closing the budget? Willis et al. [2008] failed to close the sea level rise budget using a combination of Argo, GRACE, and Jason-1 data Suggested possible systematic errors in the observing systems. Total sea level Black line: Jason-1 Grey line: Argo+GRACE Willis et al. [2008]

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. Building a climate data record • 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. Steric sea level analysis STAR produced monthly fields of steric sea level variations using a method that removed WOCE climatology before interpolation Trends in steric sea level 2004 – 2008 The budget analysis in Leuliette and Miller [2009] excluded 2003 because of poor coverage of the Southern Hemisphere.

9. 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 Peltier (2004,2009) Unpublished (Proudman)

10. 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)

11. Closing the budget Results of Leuliette and Miller [2009] Blue lines: Direct observations Red lines: Inferred from budget equation SLtotal = SLsteric + SLmass

12. Conclusion: Closing the budget • 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.

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)