Abstract
Multiple lines of observational evidence indicate that the global climate has been getting warmer since the early 20th century. This warmer climate has led to a global mean sea level rise of about 18 cm during the 20th century, and over 6 cm for the first 15 years of the 21st century. Regionally the sea level rise is not uniform due in large part to internal climate variability. To better serve the community, the uncertainties of predicting/projecting regional sea level changes associated with internal climate variability need to be quantified. Previous research on this topic has used single-model large ensembles with perturbed atmospheric initial conditions (ICs). Here we compare uncertainties associated with perturbing ICs in just the atmosphere and just the ocean using a state-of-the-art coupled climate model. We find that by perturbing the oceanic ICs, the uncertainties in regional sea level changes increase compared to those with perturbed atmospheric ICs. Thus, in order for us to better assess the full spectrum of the impacts of such internal climate variability on regional and global sea level rise, approaches that involve perturbing both atmospheric and oceanic initial conditions are necessary.
Highlights
Observations indicate that since the mid-20th century, ocean heat content is increasing [1,2], ice caps and mountain glaciers are retreating [3,4,5], and the Greenland and Antarctic ice sheets are losing mass [6,7,8,9,10,11,12]
We investigated the influence of perturbing ocean initial conditions vs. perturbing atmospheric initial conditions on projected/predicted regional and global sea level rise (SLR) through analyzing three sets of ensemble simulations using a coupled climate model—CCSM version 4 (CCSM4)
Our results show that perturbing the ocean initial conditions in general can produce larger variance on regional sea level change than perturbing the atmospheric initial conditions, on a multi-decadal timescale
Summary
Observations indicate that since the mid-20th century, ocean heat content is increasing [1,2], ice caps and mountain glaciers are retreating [3,4,5], and the Greenland and Antarctic ice sheets are losing mass [6,7,8,9,10,11,12]. Multiple studies have indicated that regional sea level rise (SLR) is not uniform, and could be significantly different from the global mean and among different regions because of the internal climate processes In the multi-model ensemble such as CMIP5, both regional and global mean SLR projections can be significantly different from one model to another under the same external forcing conditions [13,22,31]. Since the CMIP5 multi-model ensemble shows wide spread of projected global mean SLR under the same external forcing which may have hinted at an important role for the oceanic initial state, here we assess how perturbing the oceanic initial state will affect simulated regional and global mean SLR in comparison with perturbing just the initial atmospheric state using a single model—CCSM version 4 (CCSM4).
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