Changes in past, present and future sea level, focusing on the Norwegian west coast J. E. Ø. Nilsen, K. Richter og H. Drange Assessing sea level during the last 50 years Status for today s sea level Estimate sea level for the 21st og 22nd century Focus on west coast of Norway
Outline 1. About the project 2. Background on sea level rise 3. Global sea level rise 4. Regional differences 5. Regional and local results
Changes in past, present and future sea level, focusing on the Norwegian west coast The project 1 Sea level changes last 50-100 years. Observed sea level, thermohaline changes, land rise 2 Ditto using numerical models 50 years 1 Past and future (IPCC-runs and NorESM later this year) 2 Downscaling (WRF) 3 Prehistoric and future sea and land level changes 100-120 thousand years past Simplified models for glaciers Quantification of uncertainties and outer bounds 4 Synthesis focussing on relevance for the Norwegian coast Funded by City of Bergen MARE-participant Duration: 2009-2012
Background on sea level rise
Ocean temperatures rise
Observed changes in heat content of the world oceans (0-700 m) Ocean temperatures rise Heat Content (10 22 J) Potentially contribute 20-30 cm this century Year Levitus et al. (2009)
Glaciers are melting
Muir Glacier, Alaska August 1941 August 2004
Number of growing and shrinking glaciers in the world New Guinea Africa New Zealand Scandinavia 1905 1925 1945 1965 1985 05 Central Europe Glaciers are melting South America Potentially contribute 20-30 cm this century Northern Asia Antarctica Central Asia North America Arctic Worldwide World Global Monitoring Service (2008)
Ice sheets are melting
Melting Greenland Velicogna, 2009
Melting Antarctica The ice sheets are melting Potentially contribute 50+ cm this century (but there are high uncertainies connected to this) Velicogna, 2009
In sum: Sea level is rising (and will continue to rise)
Global sea level rise
Global sea level from tidal gauges and satellites (1870-2009) Global sea level (cm) 1. Now rising by 3 mm/year 2. Accelerating 3. Faster than stated in IPCC-2007 Church & White (2006) + AVISO
Observed global sea level from satellites (january 1993 june 2009) Global sea level (cm) 1993-2003 2003-2008 Greenland Antarctica Glaciers Expansion
Estimates for the future Global (recent literature) Minimum 50 cm Maximum 150 cm During this centrury For local changes in sea level, we need to consider - Global sea level change - Regional deviations - Land rise For storm surges comes additional (possible) changes in the wind climate
Regional differences
Observed sea level trends, by satellites (Oct 1992 - Jan 2008) Cazenave et al. (2008)
Distribution of future sea level change (cm) (deviations from mean change) IPCC (2007)
The effect of land uplift Isostatic postglacial rebound from the Fenno- Scandinavian ice sheet (mm/year) 11 mm/yr! 1,7 mm/yr Ekman (1996)
The effect of land uplift Approximate sea level rise between year 2100 and year 2000 relative to land surface Little change 40 cm 50 cm 60 cm 70 cm Ekman (1996)
Estimated sea level rise (cm), år 2100 vs år 2000 Uncertainty: ±25 cm Drange et al. (2007) Factors summarised: Thermal expansion Melting of land based ice Changes in ocean circulation Differences in heat uptake Land rise
Local sea level is a complex issue To be approached using different tools Different types of data Coastal stations Tidal gauges Land rise Air pressure Wind Hydrography Numerical models Altimetry Regional hydrography Factors summarised: Thermal expansion Melting of land based ice Changes in ocean circulation Differences in heat uptake Land rise
Regional and local results
Regional sea level rise 1950-2010 (model) 1948 1993 2008
Regional sea level rise 1993-2008 (observed) 1993 2008
Observed regional warming Temperature upper 30 m Plan: Most complete hydrographic database available Profiles Temperature and salinity Calculate thermal and haline contributions to change In time and space In concert with: Time series from coastal stations Bergen Remote Sensing Center NGF symposium 2010 Geilo, 17. september 2010
Local and global sea level rise 1960-2006 Local sea level rise weaker due to land uplift Bergen Remote Sensing Center NGF symposium 2010 Geilo, 17. september 2010
Different contributions Warming in the last two decades Bergen Remote Sensing Center NGF symposium 2010 Geilo, 17. september 2010
Reconstruction vs. observed Explains 72% of variability Bergen Remote Sensing Center NGF symposium 2010 Geilo, 17. september 2010
Unexplained part and wind More refined wind-driven component needed But provides lacking positive trend Bergen Remote Sensing Center NGF symposium 2010 Geilo, 17. september 2010
Also at other locations Local sea level rise weaker due to land uplift Warming in the last two decades First step towards reconstruction: Land uplift Inverse barometer effect Thermal component Haline component Explains 50-85% of variability Missing from the reconstruction/next steps: Global land ice melting More refined wind-driven component These will provide lacking positive trends Remote Sensing Center NGF symposium 2010 Geilo, 17. september 2010 Tromsø Ålesund Bergen Stavanger Trægde
Including the North Sea region Tromsø Narvik Heimsjø Bergen Aberdeen Northshields Oslo Stavanger Trægde Esbjerg Cuxhaven Remote Sensing Center NGF symposium 2010 Geilo, 17. september 2010
Summary Continued reduction of Greenland and Antarctic ice sheets may lead to global rise of 100 cm this century Sea level rise in Bergen unlikely outside the 50-100 cm range by 2100 For regional and local predictions the effect of the different components must be assessed Land uplift, air pressure, thermal expansion, and haline contraction explains 50-85% of variability Local sea level rise weaker due to land uplift Warming in the last two decades Wind component to be refined and included predictions will have to be updated regularly (i.e. new knowledge every 5-10 years)