Sea Level RiseBert Vermeersen, TU Delft (from July 1 2012 also at NIOZ – Texel)

Sea Level Change Traditionally Observed by Tide Gauges(Relative sea level change w.r.t. land)

(sea level change w.r.t. Center of Mass of the Earth;NOT w.r.t. land)

Sea Level Change Observed by Satellite Altimetry …(C

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rtesy:

Ste

ve N

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m)

… as Derived from Spatially Highly Variable Ups and Downs …

(Courtesy: Steve Nerem)

3.2

± 0.4

Sea Level Change by Continental Ice ChangesRelative sea level variations due to continental ice mass changes have never been uniform, are not uniform today, and will never be uniform due to accompanying

1. gravity changes

2. solid-earth deformation, and

3. induced changes in Earth rotation (polar wander)

Sea Level Rise: Two Principle Causes1. Thermal Expansion (heating of the oceans)

2. Continental Ice Changes (present and past)

Relative Sea Level Change Fingerprinting

Ice sheet formation: near fieldinstantaneous effect

Ice sheet melt: far fieldlong-term viscous effect

True Polar Wander Geodynamic mechanisms

leave their characteristic regional records, from which the cause(s) of relative sea level change might be determined

2,200 km

6,700 km

Gravity

Deformation

Rotation

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)

Partitioning 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.

Surface Mass Balance (SMB) Model vs. GRACE

Postglacial Rebound: Viscoelastic Deformation

ice load

bulgebulge

viscous flow

Ice Load at Last Glacial Maximum

RSL Change since Last Glacial Maximum 18,000 years ago

Sea Level Change Since Last Glacial Maximum Present-Day RSL Change Due to Glacial Isostatic Adjustment

A vexing problem: how to disentangle postglacial rebound from present-day mass changes over Antarctica ???

GRACE: observes mass changes ICESat & CryoSat: ice height changes

Satellite Gravity Satellite Altimetry

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 smoothing R.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.