Detection and attribution of 20th century sea-level rise
Changes in 20th century sea level are driven by a range of natural and anthropogenic forcings. In this seminar, I will take you through some methods that can help us understand how global and regional sea level respond to different types of external forcings. I will compare CMIP5 climate model data to observed sea-level changes, using a range of historical CMIP5 experiments with different external forcing scenarios. With this I will show that greenhouse gas forcing is one of the main drivers of late 20th century sea-level rise, both in the individual thermosteric and ocean dynamical components as well as in the total sea-level rise. For the period 1970-2005, anthropogenic forcing (greenhouse gases + aerosols) accounts for 69 +/- 31% (2 s) of the observed global mean sea-level rise. However, I will also show that natural forcings, such as volcanic eruptions, should not be neglected as they drive most of the short-term variability in sea-level change.
Figure: EOF1 (left) and explained variance (right) of the CMIP5 ensemble mean historical simulation (1861-2005) steric/dynamic sea-level change for the natural-only scenario (upper) and GHG-only scenario (lower).