Explaining the spread in global mean thermosteric sea level rise in CMIP5 climate models

Angelique Melet (LEGOS / CNES, France)


Benoit Meyssignac (LEGOS / CNES, France)

Event: 2015 Ocean Surface Topography Science Team Meeting

Session: OSTST Opening Plenary Session

Presentation type: Type Keynote/invited

The ocean stores more than 90% of the energy excess associated with anthropogenic climate change. The resulting ocean warming and thermal expansion is a leading contributor to global mean sea level (GMSL) rise. Confidence in projections of GMSL rise therefore depends on the ability of climate models to reproduce global mean thermosteric sea level (GMTSL) rise over the 20th century.
In this study, we first compare the GMTSL of climate models of the Coupled Models Intercomparison Project Phase 5 (CMIP5) to observations over 1961-2005.
Although the model-ensemble mean is within the uncertainty of observations, the model ensemble exhibits a large spread. We then aim at explaining the spread in CMIP5 climate models GMTSL over the 20th and 21st centuries. We show that climate models' GMTSL rise linearly depends on the time-integrated radiative forcing F (under continuously increasing radiative forcing).
The constant of proportionality (nu) expresses the transient thermosteric sea level response of the climate system. nu depends on the fraction of excess heat stored in the ocean, the expansion efficiency of heat, the climate feedback parameter and the ocean heat uptake efficiency.
The across-model spread in nu explains most (>70%) of the across-model spread in GMTSL rise over the 20th and 21st centuries, while the across-model spread in time-integrated F explains the rest. The time-integrated F explains less variance in the across-model GMTSL rise in 21st than in 20th century simulations, as the spread in F is reduced over the 21st century because the anthropogenic aerosol forcing, which is a large source of uncertainty in F, becomes relatively smaller.

Keynote/invited presentation show times:

RoomStart DateEnd Date
Grand Ballroom 1 Tue, Oct 20 2015,11:40 Tue, Oct 20 2015,12:00
Angelique Melet