Sea Level

Question 1

Dawson (2019)

Introducing Sea Level Change

Answer 1

• Relative sea level (view from the beach)-land/sea move
  -earth’s sea surface not flat - oceans different elevations eg Indian Ocean -110m below average (diff gravitational pull) - geoidal sea surface
• 2006 inconvenient truth sea level rise - Maldives still here - CC impact sea level not simple melt = global rise
• evidence former sea level - landforms, raised beaches, coral reefs, submerged features, sediments, fossils, radio carbon dating
• long-term sea level change - G/IG, ice sheets, holocene
• global sea level curves (abandoned science - problem media focus global change + CC - IPCC reports)
• response earth’s crust sea level change - ocean basins under weight ocean mass drop, pressure under ice sheets, forebulges etc
• stage 5e
• antarctic and greenland ice sheets (WAIS - west antarctic ice sheet stable, unlikely to collapse, if did grounding line) (Greenland more impact CC) (most CC melt is small ice caps and mountain meltwater retreat glaciers)
• CC and thermal expansion - also human eg. GW use = increase sea level
• meltwater pulses, Younger Dryas, Lake Agassiz
  KEY TERMS
• Geoidal eustasy (gravity sea water distribution)
• tectono-eustasy (water displaced relative land by crust)
• glacial isostasy (lithosphere depressed ice sheet - rebound)
• hydro-isostasy (deformation ocean floor water loads)
• steric changes (change ocean volume, not mass)

Question 2

Isostatic Rebound Evidence CS

Answer 2

Celcius rock Lovgrunde Sweden

• 1530 sea level at top rock
• 1563 0.4m lower
• 1731 2.4m lower than 63
• 1731-1829 = 0.76m lower
• swedes thought sea lowering due to water use - but actually seeing isostatic rebound as result glaciers

Question 3

Sea Level CS 1

Answer 3

UK

• GMSL rise (meltwater) and isostatic adjustment big reasons sea level difference (isostatic rebound)
• sea level helps understand past eg. location British-Irish ice sheet

Question 4

Sea Level CS 2

Answer 4

USA East Coast (hotspot - short term changes response)
- ocean current changes, slowing Gulf Stream (but Gulf Mexico also hot spots so not best explanation), El Nino and NAO - ENSO shift with el nino

Question 5

GW Extraction EG

Answer 5

Vietnam

Question 6

Barrier Systems EG

Answer 6

US East coast has many
- N Carolina expensive community on one - threat sea level - so N Carolina made it illegal to discuss sea level in reference coastal barrier systems

Question 7

Types Estuaries

Answer 7

1. salt wedge - Mississippi
2. Partially Mixed - Thames, Chesapeake Bay
3. well mixed - The Severn, Firth of Forth, Bay of Fundy
4. Fjord-type - Nuuk fjord Greenland

Question 8

Hazards - Hurricane EGs

Answer 8

• Sandy 2012 - 50 bn damage, 2 deaths
• Katrina 2005 - 128 bn damage, 1245 deaths
• Hurricane Irma 2017

Question 9

Nortable North Sea Floods

Answer 9

2013 - most serious tidal surge 30 years, 0 deaths, lot damage = £426mn
1953 - most severe Netherlands, 2533 deaths, 307 in UK, £50mn (£1.26bn today)
17033 England, Belgium, Netherlands and Germany - thousands deaths

Question 10

Flood Mitigation EG

Answer 10

Thames Barrier

Question 11

Coast Protection Body UK

Answer 11

• Defra responsible flood and coastal erosion risk management but does not built or manage defences themselves - gov grants
• Environment Agency established 1995 = public body of Defra - England and Wales flood risk management

Question 12

Model for future prediction - IPCC

Answer 12

IPCC Emission Scenarios

2. 6 (CO2 peak 2100), 4.5 (stable 2100), 6, 8.5 (no peak in CO2 by 2100)
   - fourth report IPCC - AR4 (2007) and fifth - AR5 (2013)
   - AR4 sea level rise projected 0.18-0.59m
   - AR5 range estimates 0.26-0.82m by 2100

Question 13

Jevrejeva et al (2016)

Answer 13

• GHG emissions are following RCP 8.5
• after 2040 if warming well over 2 degrees, global sea level rise over 10mm year by 2083
• limited adaptation time

Question 14

Kopp et al (2016)

Answer 14

• C20th sea level rise faster than 27 previous centuries

- semiempirical modelling shows without global warming GSL C20th would risen 3-7cm not 14cm observed

Question 15

future sea level change CS

Answer 15

UK - UKCPO9

• estimating relative sea level change UK
• gravity changes due Greenland / Antarctica ignored

Question 16

Valle-Levinson (2017)

Answer 16

Eastern US hotspots

• short sea level rise accelerations or hotspots occurred eastern US past 95 years and hotspots positions determined by North Atlantic Oscillation (ENSO/ el nino)
• coastal communities threat storm surges, land and water resource loss - need understand regional change
• North Cape Hatteras hot spot SLR exceeds global mean sea level - weakening gulf stream, decreased overturn
• location hotspot migrates so not just one thing - gulf stream, NAO, ENSO - combination

Question 17

Horton et al (2018)

Answer 17

• need to understand future sea-level change due to hazards it creates and to do so must understand drivers sea level and past (past-present-future)
• need understand relationship sea level and climate forcing - hard with records just 60 yrs data - proxies valuable archives sea-level response past climate = better basis for projecting
• difference in regional changes from global mean - REGIONAL KEY management and projection
• Relative sea level vs global mean sea level
• sea-level fingerprints = geographic pattern of sea level change following rapid melting of ice sheets / glaciers - essentially changes sea level response ice / water storage
• Glacial isostatic adjustment - response of earth to mass redistribution during glacial cycle - isostasy = where deformation occurs in attempt to return earth equilibrium - GIA = isostatic deformation related to ice / water loading in glacial cycle - response change mass store - thus GIA models simulate evolution earth based ice-sheet history - glacial phase depression land beneath ice sheets = migration mantle material away from ice-load centres = forms forebulge in regions adjacent to ice sheets - when ice sheets retreat mantle material flows back former load centres = postglacial rebound where forebulge retreats and collapses
• sediment compaction = reduction volume sediments due to decrease pore space = lowers heigh earth surface (can occur due to human eg. GW extraction)
• use of radiocarbon dating, tide-gauges, satellites determine sea level changes
• approaches to projection - models - IPCC scenarios - also bottom-up (based drivers) (central range estimates and high-end estimates and probabilistic) or top-down (metrics of change) (semi-empirical = historical or expert = joint experts knowledge) - science focused
• end C21st end point GMSL projections not far enough - CC and system lags!
• 11% pop live coastal areas less 10m above sea level