Sea level over glacial cycles.

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2 Sea level over glacial cycles. T1: 1 m/century With short periods of with rates up to 4m/century LIG Sea level higher than today (+9m) Siddall et al Very stable sea level in human history. Image created by Robert A. Rohde / Global Warming Art

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4 Global Sea Level Rise The world is warming and this causes sea level to rise because: 1 Warming melts the large ice masses on Earth. AND WE SEE THIS HAPPENING 2 As the oceans are warming the water expands.

5 The Greenland Ice Sheet margins are thinning and outlet glacier flow has increased Elevation change Sørensen et al. (DTU-Space) +7m Rignot et al Jakobshavn Img Credit Konrad Smiarowski

6 The Antarctic Ice Sheet is losing mass (Especially West Antarctic) Pritchard et al m

7 Glaciers and Ice caps are shrinking Small total volume (<0.5m) But very important because they can react fast to climate change Image created by Robert A. Rohde / Global Warming Art

8 Ocean Heat Content is increasing Levitus et al. 2012

9 Sea level is rising Tide-Gauges & Satellite altimetry 20 th Century rate 1.8 mm yr -1 Satellite rate since mm yr -1 Tide-gauge rate since mm yr -1 Jevrejeva et al. 2008

10 Process based models Emission scenario Atmosphere-Ocean GCM Thermal expansion Surface Mass Balance Snow pack, melt Greenland Antarctica Mountain Glaciers (hundreds of thousands) Freshwater fluxes to ocean

11 Earlier work: Mid-range estimate, and High end Scenario * 15cm 7+7 cm 21-7 cm 22 cm

12 Earlier work: Mid-range scenario (A1B, ΔGMSL=70cm) Local Sea Level Rise Glacial Isostatic Adjustment

13 RCP85: no mitigation to speak of RCP60: some mitigation RCP45: quite a lot of mitigation RCP26: impossible mitigation Source: Gavin Schmidt IPCC AR RCP8.5 RCP2.6

14 We cannot predict the fate of Antarctica In summary, ice-dynamics theory, numerical simulations, and paleo-records indicate that the existence of a marine-ice sheet instability associated with abrupt and irreversible ice loss from the Antarctic ice sheet is possible in response to climate forcing. However, theoretical considerations, current observations, numerical models, and paleo records currently do not allow a quantification of the timing of the onset of such an instability or of the magnitude of its multi-century contribution. IPCC AR5

15 Marine ice sheet instability Thinning > increased flotation > speed up > stretching & further thinning

16 The bedrock beneath the Antarctic Ice sheet bedmap2

17 WAIS is already collapsing Recently Favier et al. (2014), Rignot et al. (2014) and Joughin et al. (2014) have found that the Amundsen Sea sector of Antarctica is already engaged in an unstable/irreversible retreat.

18 Mouginot et al. 2014

19 IPCC AR Worst case is much worse Projections conditional on no marine instability Problem: How can we possibly quantify an upper limit then?

20 An ice sheet expert elicitation Performance weighted combined uncertainty distribution. (Bamber & Aspinall, 2013) Pros: unconditional uncertainties. Experts on the key uncertainty. Includes risk & potential rate of collapse +generally cool people! Criticism: Not tied to scenario, merely opinions, small sample.

21 Red: AR5 Gray: AR5+Experts Covariant uncertainties Greater tail-risk

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24 Dynamic Sea Level

25 Regional projections using AR5,rcp8.5 + BA13 Static-equilibrium Fingerprints Ocean dynamics Glacial Isostatic Adjustment

26 Fennoscandian Glacial Isostatic Adjustment GIA Hill et al. (2010) combined estimate using data from GPS (bifrost), GRACE and Tide-gauges. ΔRSL = ΔLSL + ΔGIA

27 Huge waves engulf the seafront in Porthleven, Cornwall. Photograph: Annabel May Oakley-Watson/REX

28 RCP8.5

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30 Long-term sea level rise Greenland thickness: 3 km (= 10 Eiffel towers) It will take a long time to melt it all.

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32 RCP8.5 Jevrejeva et al.2011

33 If all the ice melted

34 ECP3PD: ~370ppm Current conc. ECP6: ~750ppm ECP4.5: ~640ppm ECP8.5: ~2650ppm 50MYR Correlation Causation Ice free planet Greenland + WAIS gone, Present day Sea level RCP85: no mitigation to speak of RCP60: some mitigation RCP45: quite a lot of mitigation RCP26: impossible mitigation Source: Gavin Schmidt Paleo-correlation plot from Foster&Rohling 13 Note: Correlation Causation

35 Welcome to New Copenhagen! An artists fictional map ain t gonna happen for a very long time. Credit: JaySimons

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37 Why do we care? Example: The stormsurge of 1872 Gyldendal/Illustreret Tidende Southern Lolland (Rødby): +3m Gedser: +2.6 South-Eastern Jutland: +3.6m Source: Den Store Danske Encyclopædi

38 Why do we care? The Rødbyhavn tide gauge Water level relative to yearly mean sea level (cm) Protect against: 1.65m above mean sea level. 50cm sea level rise Consequence: Flooded every year! Infrastructure design criteria: Protect against 100yr storm surges.

39 The estimated multiplication factor (shown at tide gauge locations by colored dots), by which the frequency of flooding events of a given height increase for a mean sea level (MSL) rise of 0.5 m

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