Is sea level rise larger near the coast?Is sea level rise larger near the coast?

Remko ScharrooAltimetrics LLC, Cornish, New Hampshire

Eric Leuliette and Laury MillerNOAA / Laboratory for Satellite Altimetry, Silver Spring, Maryland

2Remko Scharroo — Is sea level rise larger near the coast? — AGU Fall Meeting, 18 December 2009

Is sea level rise larger near the coast?

• Not an arbitrary question ...– Sea level rise in the middle of the ocean is rather academic– Coastal sea level rise is most important to our society

3Remko Scharroo — Is sea level rise larger near the coast? — AGU Fall Meeting, 18 December 2009

Is sea level rise larger near the coast?

• In support of the affirmative– Sea surface temperature near the coast rises faster– Tide gauges show a rate larger than altimeters

• In support of the contrary– Drop in sea level expected around Greenland and Antarctica

Sea surface temperature change (2002-2009)

4Remko Scharroo — Is sea level rise larger near the coast? — AGU Fall Meeting, 18 December 2009

Is sea level rise larger near the coast?

• Probably YES– Jason-1 (2002-2009)– Coastal sea level rise clearly and significantly larger

3.0

4.8 mm/yr

5Remko Scharroo — Is sea level rise larger near the coast? — AGU Fall Meeting, 18 December 2009

Is sea level rise larger near the coast?

• Probably …Pierre Prandi et al. (2009):– TOPEX/Jason-1 (1993-2007), GIA corrected

6Remko Scharroo — Is sea level rise larger near the coast? — AGU Fall Meeting, 18 December 2009

Is sea level rise larger near the coast?

• Probably NO

Global and coastal sea level rise from satellite altimetry and tide gauges (Prandi et al., 2009). 12-month running average. GIA corrected. Values in mm/yr.

1993-2002 1993-2007

Global 3.4 ± 0.2 3.4 ± 0.1

Coastal (<200 km) 4.4 ± 1.0 3.3 ± 0.5

Be wary of claims of a 0.1 mm/yr error bar!

7Remko Scharroo — Is sea level rise larger near the coast? — AGU Fall Meeting, 18 December 2009

EOFs of sea level rise

• Jason-1 (2002-2009) EOF 1 (15% of variance)– Annual variation– High energy currents and tropical oscillation

8Remko Scharroo — Is sea level rise larger near the coast? — AGU Fall Meeting, 18 December 2009

EOFs of sea level rise

• Jason-1 (2002-2009) EOF 2 (9% of variance)– Annual variation, 3 months out of phase with EOF 1– Tropical and subtropical oscillation

9Remko Scharroo — Is sea level rise larger near the coast? — AGU Fall Meeting, 18 December 2009

EOFs of sea level rise

• Jason-1 (2002-2009) EOF 3 (7% of variance)– Interannual variation, overall rise– Strong rise in Western Pacific = Coastal and ENSO

10Remko Scharroo — Is sea level rise larger near the coast? — AGU Fall Meeting, 18 December 2009

Results from 7 altimeters

• Global sea level trend (1992-2009)– No GIA correction (~0.3 mm/yr)– 5 mm annual amplitude– Overall trend 2.75 ± 0.2 mm/yr

11Remko Scharroo — Is sea level rise larger near the coast? — AGU Fall Meeting, 18 December 2009

Results from 7 altimeters

• Coastal (<200 km) sea level trend (1992-2009)– No GIA correction (~0.2 mm/yr)– Significantly larger annual amplitude (heating mostly?)– Slightly but not significantly larger trend (2.90 mm/yr)

12Remko Scharroo — Is sea level rise larger near the coast? — AGU Fall Meeting, 18 December 2009

Conclusion?

• Is sea level rise (significantly) larger near the coast?– NO– But it isn’t smaller either!– And … was it really useful to ask the question in the first place?– Don’t we have to worry most about places with a lot of people

living near a shallow coast?

13Remko Scharroo — Is sea level rise larger near the coast? — AGU Fall Meeting, 18 December 2009

Question rephrased…

• What’s the sea level rise in “my backyard”?

Mediterranean North Sea

Gulf of Mexico S. China Sea

GIA: +0.3 GIA: +0.0

GIA: +1.9 GIA: -0.4

14Remko Scharroo — Is sea level rise larger near the coast? — AGU Fall Meeting, 18 December 2009

Or rephrased again …

• Where don’t I want to plant my backyard?

• Where is the largest impact of sea level rise?

GIA: +1.9 GIA: +0.0