Impacts Sealevel Change Mark Cresswell 69 EG 6517

  • Slides: 16
Download presentation
Impacts: Sea-level Change Mark Cresswell 69 EG 6517 – Impacts & Models of Climate

Impacts: Sea-level Change Mark Cresswell 69 EG 6517 – Impacts & Models of Climate Change

Topics • Introduction • Measuring sea-level change • Some facts • Summary

Topics • Introduction • Measuring sea-level change • Some facts • Summary

Introduction • The term “sea-level change” refers to a change in the mean-sea-level for

Introduction • The term “sea-level change” refers to a change in the mean-sea-level for sentinel ports across the globe • MSL is the average of high and low water marks • Tidal surges may occur as a result of storm events – making coastal zones vulnerable but not necessarily due to a change in MSL • Sea-level change is primarily due to thermal expansion and not “more water”

Measuring Sea-level Change • Changes in sea-level are recorded by the Permanent Service for

Measuring Sea-level Change • Changes in sea-level are recorded by the Permanent Service for Mean Sea Level (PSMSL) at the Proudman Oceanographic Laboratory (POL) on Merseyside • Tide gauge data from around the world are collated at POL and trends in sea level are derived from time series extending back many decades or even centuries

Measuring Sea-level Change

Measuring Sea-level Change

Measuring Sea-level Change • Sea-level is routinely measured from altimetric satellites such as TOPEXPOSEIDON

Measuring Sea-level Change • Sea-level is routinely measured from altimetric satellites such as TOPEXPOSEIDON and JASON • The significant wave height is determined from the return time of energy emitted from TOPEX • As water expands in response to thermal forcing, TOPEX can be used to derive a proxy of SST as well as wave height

Measuring Sea-level Change

Measuring Sea-level Change

Measuring Sea-level Change • Jason-1 is a new altimetric satellite designed to follow on

Measuring Sea-level Change • Jason-1 is a new altimetric satellite designed to follow on from the TOPEX POSEIDON mission

Measuring Sea-level Change

Measuring Sea-level Change

Some facts • Some components of future sea-level rise can be modelled regionally using

Some facts • Some components of future sea-level rise can be modelled regionally using coupled oceanatmosphere models • The most common method of obtaining scenarios is to apply global mean estimates from simple models • Changes in the occurrence of extreme events such as storm surges can lead to major coastal impacts

Some facts

Some facts

Some facts • Global mean sea-level has risen by about 0. 10. 2 mm

Some facts • Global mean sea-level has risen by about 0. 10. 2 mm a year over the past 3000 years and by about 1 -2 mm a year since 1900 with a central value of 1. 5 mm per year • It is believed (IPCC) that sea-level will rise by 0. 09 -0. 88 metre between 1990 and 2100 • Higher MSL will increase the frequency of existing extreme levels associated with storm waves and surges.

Some facts • Sea-level will tend to increase in association with a warmer climate

Some facts • Sea-level will tend to increase in association with a warmer climate as a result of: – Thermal expansion of seawater – Melting of small mountain glaciers and ice caps – Melting of the Greenland ice cap – Changes in the mass balance of the Antarctic ice cap

Some facts • As seawater warms, its density decreases – thus a given mass

Some facts • As seawater warms, its density decreases – thus a given mass of ocean water will occupy a greater volume as the ocean warms – thereby tending to increase the average sea level • A globally uniform ocean warming by 3ºC would cause a sea-level rise of about 2. 4 m • Complete melting of all mountain glaciers and ice caps is estimated to raise sea level by some 50± 10 cm (Harvey 2000 after Warrick et al. 1996)

Some facts • Greenland is of particular concern because of its large ice mass

Some facts • Greenland is of particular concern because of its large ice mass – enough to raise sea-level by about 7. 4 m if it was to melt • A regional warming of about 6ºC would be sufficient to provoke the eventual melting of the entire ice mass (Letréguilly et al. 1991) • Some models show that increased temperatures lead to enhanced snowfall over both Greenland Antarctic ice sheets – however Greenland ice cores show a reverse relationship

Contribution to SL rise (cm) from 1990 to 2100 (Harvey, 2000) Reference T (ºC)

Contribution to SL rise (cm) from 1990 to 2100 (Harvey, 2000) Reference T (ºC) Glaciers & Greenland ice caps Antarctica Thermal expansion Total Wigley & Raper (1995) 2. 1 11. 9 - 19. 4 -- -- De Wolde et al. (1997) 2. 2 12. 3 7. 2 -7. 5 15. 2 27 2. 5 14. 6 10. 4 -8. 5 17. 5 34 2. 7 13. 2 7. 6 -7. 9 22. 5 35 3. 3 18. 2 9. 3 -9. 7 29. 9 48 1. 3 -- 3. 9 0. 7 -- -- 2. 4 -- 10. 5 -3. 0 -- -- 3. 5 -- 20. 8 -6. 4 -- -- -- 15 ± 5 -- Gregory & Oerlemans (1998) Huybrechts & de Wolde (1999) Bryan (1996)