Eddy variability contribution to decadal regional sea level trends

Sea level rise is one of the most direct consequences of the actual global warming. Over the 20^th century, global mean sea level rises at a rate of 1.5-2 mm. yr^-1. Since the beginning of the 1990s, satellite altimetry measure the changes of sea level with a near global coverage (from 66^oS to 75^oN). The use of satellite altimetry has, for the first time, highlighted large regional variability in sea level trends that significantly differ from the global mean estimate. If global ocean warming and land ice melting (mountain glaciers and ice sheets from Greenland and Antarctica) are the main processes explaining the observed global mean sea level rise, at regional scales, other processes are involved, such as changes in salinity or temperature associated with ocean circulation or air-sea fluxes at the ocean surface.

 

Sea level projections used in IPCC reports are based primarily on coarse-resolution coupled climate models. Current projections are based on climate models in which ocean-eddy variabilities are parameterized and results deviate from observations especially in the Southern Ocean. Mesoscale processes transport heat/freshwater over very large distances in the ocean (both horizontally and vertically). They also regulate energy, moisture and carbon exchanges between the oceans and the atmosphere via coupling. Understanding these processes and how they might change in the future is critical for portraying robust regional sea level change.

 

Recently, new generations of climate models have been integrated at spatial resolutions of ¼° and 1/12°, which is sufficient to partially resolve the mesoscale eddy variability. These higher resolutions enable the study of the impact of mesoscale eddies on regional sea level changes and how these processes may change in the future.

 

In this work, we will take advantage of a suite of climate model simulations based on HadGEM3-GC3.1 at different spatial resolution (1°, ¼° and 1/12°) to assess the contribution of eddy-variability on regional sea level trends. We first present the ability of such climate models to reproduce regional sea level trends observed by satellite altimetry over decadal to multi-decadal time periods. Second, temperature and salt budget will be presented to quantify the contribution of eddy variability on these regional sea level trends.