Assessment of the 20th century global mean sea level rise in CMIP5 historical runs using observations

Angelique Melet (LEGOS / CNES, France)

CoAuthors

Benoit Meyssignac (LEGOS, France); Robin Chevrier (LEGOS, France); Xavier Fettweis (Université de Liège, Belgium); Marzeion Ben (Innsbruck University, Austria); Elsa Bourgeois (LEGOS, France); Anny Cazenave (LEGOS, France); David Salas y Mélia (CNRM-GAME, France)

Event: 2014 Ocean Surface Topography Science Team Meeting

Session: Science Results from Satellite Altimetry: Regional and basin-scale processes and sea level rise

Presentation type: Type Poster

Sea level rise is one of the most adverse consequences of climate change. To assess the potential impacts of future sea level rise it is essential to estimate the most accurate and reliable sea level rise projections. However, current sea level rise projections are based on climate models and are highly uncertain, essentially because of inappropriate (or sometimes missing) model representations of some physical or dynamical processes that affect sea level in the climate system.

In this study, we propose a new method to estimate the 20th century global mean sea level (GMSL) rise and its contributors from the Climate Model Intercomparison Project Phase 5 (CMIP5) climate model outputs. Over the 20th century, contributors to GMSL are essentially ocean warming, glaciers ice melt, land water storage changes and Greenland surface mass balance (Gregory et al. 2013). Thermal expansion is computed from the 3D temperature and salinity fields. Different reference levels are used to estimate the contribution of the deep ocean. The 20th century thermal expansion is corrected from the model drifts and omission of volcanic forcing in the pre-industrial control runs. Glacier mass loss is estimated from an offline glacier model forced by climate model air temperature and precipitations (Marzeion et al. 2012). Greenland surface mass balance is estimated from a new statistical downscaling method based on a regionalization of the Fettweis et al. (2013) method. Land water storage changes are estimated from the literature.

We then aim at reducing the uncertainty of the ensemble of available climate models by validating each climate model estimates of the 20th century sea level rise and of its contributors against observations (from satellite altimetry and tide gauge records for the sea level, from in situ ocean temperature observations for thermal expansion, and from glaciers and ice sheet models forced with atmospheric reanalyses for the global ocean mass variations). In particular, altimetric sea level data and tide gauge reconstructions and their weak uncertainties provide interesting observational benchmarks to assess the ability of climate model to simulate past sea level variations. Since over the 20th century thermal expansion and glacier mass loss dominate the GMSL budget, we show that assessing in addition the ability of climate models to simulate thermal expansion with in-situ temperature and salinity data gives an interesting indirect observational constraint for the CMIP5 estimates of glacier mass loss contribution over the 20th century. Our results suggest that over the 20th century, CMIP5 models reproduce the observed ocean thermal expansion (within uncertainty) but underestimate the observed sea level rise because of small glaciers mass loss estimates.


 
Angelique Melet
LEGOS / CNES
France
angelique.melet@legos.obs-mip.fr