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
• SLtotal is total sea level
• Altimeters Jason-1, Jason-2, and Envisat
• SLsteric is 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.

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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
Willis et al. 2008 Trend 2003.52007.5
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
Suggested possible systematic errors in the
observing systems.
Total sea level Black line Jason-1 Grey line
ArgoGRACE
Willis et al. 2008
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Total sea level from altimetry

• STAR supports the development of the Radar
  Altimeter Database System (RADS)
• Worlds leading platform for sea level climate
  data records (CDRs)

• Includes latest correction products
• Supports STARs Cal/Val activities
• Intermission
• Tide gauge
• Sea level rise research
• Leuliette and Miller 2009

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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
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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.
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STAR GRACE processing

• STAR processes GRACE gravity fields into ocean
  mass variations
• Ocean mass variations observed directly from
  GRACE have little trend for 20042009.
• A complete analysis must account for ocean mass
  changes masked by geoid variations from the
  solid Earths 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)
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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)

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Closing the budget
Results of Leuliette and Miller 2009 Blue
lines Direct observations Red lines Inferred
from budget equation SLtotal SLsteric
SLmass
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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.

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-1/2 1.8 1.1
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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)