Sea level change

Credit: Andrea Pattaro/AFP/Getty Images

Sea level change monitoring using satellite geodesy data: Past, present and future predictions

Why these types of studies are important?

Sea level change will lead to changes in coastal impacts and increase environmental hazards. These changes are related to climate change that affects a lot of people’s daily life who live near coastal zone. Presently about 40% of the world's population lives within 100 kilometers of the coast and 25% of the global population lives in the near coastal zone within 100-meter elevation according to IPCC - Intergovernmental Panel on Climate Change reports. Climate change is one of the important issues today, due to its special weather conditions, which requires many studies to model the climate behavior.

Method:

For this purpose we use our knowledge of past and present observed sea level changes, as well as predicting the future sea level change using space geodesy techniques. Important factors for sea level change are the effects of ground ice changes (glaciers), land uplift due to glacial isostatic adjustment, seawater salinity, thermal expansion, and reduction of surface water storage (aquifers). We use satellite altimetry and gravimetry data (GRACE) and assimilate other in-situ data (tide gauges) as well as available hydrological and ocean circulation models to determine sea level change.

The GRACE has provided a valuable source of information about the time variable Earth’s gravity field, and more specifically water exchange as the main contributor to the Earth’s gravity field changes within decadal scales (mass component). Also, since 2004, the Argo project reached a global coverage of its floats measuring seawater temperature and salinity at different layers of ocean depth, which helps to model steric component of Global Mean Sea Level (GMSL). The following figures show the mass component, steric component and GMSL using different data centres. Generally the following relation is between GMSL and its components:

GMSL = Mass component (GRACE) + Steric Component (Argo data)

Our results show that GFZ products, applying Gaussian filter (300 km averaging radius) with a combination of JAMSTEC products (Argo data) is the best solution to determine the GMSL trend. The GMSL trend is 3.12 mm/year.

The main issues in this study were:

  • Remving the effect of glacial isostatic adjustment (GIA), land uplift, from mass-related sea leve lrise
  • Correction due to geocenter motion
  • Correction due to Earth’s dynamic oblateness
  • Different spatial smoothing filters applied on the GRACE observations

 

Figure. A) Global mass-related sea level time series using three main GRACE processing centers data (i.e. GFZ, CSR and JPL). B) Steric component i.e. salinity and temperature effect using Argo-based monthly data computed from three processing centers over January 2005-December 2014. C) Averaged global mean sea level from satellite altimetry, GFZ-DDK3 ocean mass, and the steric component from JAMSTEC products over January 2005 to December 2014 (Periodic terms (annual and semi-annual periods) have been estimated and removed, and a 3-month running mean filter has been applied. Credit: Amin H., Bagherbandi M., Sjöberg L., (2018). Global Mean Sea Level Budget Closure over January 2005 to December 2014. Submitted to Geophysical Journal International.

Published by: Zara Lindahl Page responsible: Gunilla Mårtensson Updated: 2018-11-13
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