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Sea level change over time

Laurence Vidal discusses about sea level changes over time.

In this article, we will explore changes of temperature, sea ice volume and sea level in the past, present and future.

1. Ices ages temperature and seal level changes

Source: Modified from Past Global changes/PAGES magazine

This figure shows the Antartica temperature and global sea level changes during the last several glacial/interglacial cycles from 450 thousand years ago (on the left) to the present day (on the right). The first two curves (blue and green) show local changes in temperature at two sites in Antarctica as derived from deuterium isotopic measurements (δD) on ice cores (EPICA Community Members 2004, Petit et al. 1999). The final plot shows a reconstruction of global ice volume from δ18O measurements on benthic foraminifera from a composite of globally distributed sediment cores (Lisiecki and Raymo 2005) (red curve). Horizontal lines indicate modern temperatures and ice volume. 

Changes in global ice volume is also shown as global relative sea level changes (RSL) and varies between 0 and -120 meters (compared to the present level). Lower seal level (-110 to -120 meters) compared to the present situation is observed during the last glacial maximum (c.a. 20 kyr ago) and also during the glacial periods over the last 450 kyr. Blue and green curves show the reconstructed atmospheric air temperature (at coring location in Antarctica). Changes in temperatures (∆T) compared to modern values at same location are shown and reported in °C. The changes in Antarctic temperatures are highly correlated to each other as well as with sea level curve. Global sea level changes are associated with ice cap advances and melting and is valuable markers for glacial/interglacial period.

2. Sea level rise during the last century

Source: NOAA

Observed sea level since the start of the satellite altimeter record in 1993 (black line), plus independent estimates of the different contributions to sea level rise: thermal expansion (red line) and added water, mostly due to glacier melt (blue line). Added together (purple line), these separate estimates match the observed sea level very well.

Based on these data we can make the following estimates of rates of sea level rise:

1880-2019 = 1.7mm/year*

1993-2019 = 3.3 mm/year

2009-2019 = 4.5mm/year

* Record includes historical tide gauge measurements

3. Future Projections for sea level

Source: IPCC AR6, Figure SPM.8

The projected sea level rise depends on our emissions (RED: high emissions, ORANGE: medium emissions; BLUE:  Paris Agreement emissions).

The take-away message is that for high emission scenarios, sea level will likely rise by about 1 meter, whereas if we follow the Paris Agreement, sea level rise will be closer to half a meter.

Source: Sixth Assessment Report of the IPCC

© Laurence Vidal
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