(sea level change w.r.t. Center of Mass of the Earth;NOT w.r.t. land)
(Courtesy: Steve Nerem) Sea Level Change Observed by Satellite Altimetry …
… as Derived from Spatially Highly Variable Ups and Downs … 3.2 ± 0.4 (Courtesy: Steve Nerem)
Sea Level Rise: Two Principle Causes2. Thermal Expansion (heating of the oceans)3. Continental Ice Changes (present and past)Sea Level Change by Continental Ice ChangesRelative sea level variations due to continental ice masschanges have never been uniform, are not uniform today, andwill never be uniform due to accompanying• gravity changes• solid-earth deformation, and• induced changes in Earth rotation (polar wander)
Relative Sea Level Change Fingerprinting Gravity Ice sheet formation: near field 2,200 km instantaneous effect 6,700 km Ice sheet melt: far field long-term viscous effect Deformation True Polar Wander Geodynamic mechanisms leave their characteristic regional records, from which the cause(s) of relative sea level change might be determinedRotation
ESA’s GOCE Gravity Satellite Mission(launched March 17 2009) “ half a TU Delft satellite “
Reassessment of the Potential Sea-Level Rise from a Collapse of the West Antarctic Ice Sheet,J. L. Bamber, R. E. M. Riva, L. L. A. Vermeersen, A. M. LeBrocq, Science, 324, 901-903, 2009.
NASA / DLR’s GRACE Gravity Satellite Mission (launched March 17 2002)
Surface Mass Balance (SMB) Model vs. GRACEPartitioning recent Greenland mass loss, M. van den Broeke, J. Bamber, J. Ettema, E. Rignot, E.Schrama, W. v.d. Berg, E. van Meijgaard, I. Velicogna, B. Wouters, Science, 326, 841-986, 2009.
RSL Change since Last Glacial Maximum 18,000 years ago
Sea Level Change Since to Glacial Isostatic Adjustment Present-Day RSL Change Due Last Glacial Maximum
A vexing problem: how to disentangle postglacial rebound frompresent-day mass changes over Antarctica ??? Satellite Gravity Satellite Altimetry GRACE: observes mass changes ICESat & CryoSat: ice height changes Combining gravity change with altimetry change observations might do the trick …
GRACE (gravity) data and ICESat (altimetry) data CSR RL04, SLR C20, destriped 300 km Gaussian smoothingR.E.M. Riva, B.C. Gunter, T.J. Urban, L.L.A. Vermeersen, R.C. Lindenbergh, M.M. Helsen, J.L. Bamber, B.E. Schutz, R.S.W. van de Wal, M.R. van den Broeke,Glacial Isostatic Adjustment over Antarctica from combined GRACE and ICESat satellite data, Earth Planet. Sci. Lett., 288, 516-523, 2009.
Outlook• Sea Level Change is Complicated: For many coastal regions in the world, deviations from the average global mean of 3 mm/yr relative sea level rise are observed to be large, in the range between -15 mm/yr relative sea level fall and +15 mm/yr relative sea level rise.• Global Processes, Regional Impact: Gravity Changes, Solid Earth Deformation and Earth Rotation all influence relative sea level change projections and must be taken into account, also for relative sea level changes due to present-day ice melt! Vice Versa, observing “fingerprint patterns” over the oceans might tell us more about their causes.• Satellite Observations are Essential: For reliable predictions on future regional sea level change a combination of data sets (satellite altimetry and gravity, tide gauges, GPS, …) with geophysical models (ocean dynamics, ice dynamics, postglacial rebound, …) is required.• Collaboration: Not an Option, but Necessity: fruitful collaborations already exist between TU Delft, KNMI, IMAU and other national (and international) partners on sea level and ice research. The Delft Climate Institute will further strengthen and expand these collaborations.