Global sea-level budget and ocean-mass budget, with focus on advanced data products and uncertainty characterisation

Abstract

Abstract. Studies of the global sea-level budget (SLB) and the global ocean-mass budget (OMB) are essential to assess the reliability of our knowledge of sea-level change and its contributions. Here we present datasets for times series of the SLB and OMB elements developed in the framework of ESA's Climate Change Initiative. We use these datasets to assess the SLB and the OMB simultaneously, utilising a consistent framework of uncertainty characterisation. The time series, given at monthly sampling, include global mean sea-level (GMSL) anomalies from satellite altimetry; the global mean steric component from Argo drifter data with incorporation of sea surface temperature data; the ocean mass component from Gravity Recovery and Climate Experiment (GRACE) satellite gravimetry; the contribution from global glacier mass changes assessed by a global glacier model; the contribution from Greenland Ice Sheet and Antarctic Ice Sheet mass changes, assessed from satellite radar altimetry and from GRACE; and the contribution from land water storage anomalies assessed by the WaterGAP global hydrological model. Over the period Jan 1993–Dec 2016 (P1, covered by the satellite altimetry records), the mean rate (linear trend) of GMSL is 3.05 ± 0.24 mm yr−1. The steric component is 1.15 ± 0.12 mm yr−1 (38 % of the GMSL trend) and the mass component is 1.75 ± 0.12 mm yr−1 (57 %). The mass component includes 0.64 ± 0.03 mm yr−1 (21 % of the GMSL trend) from glaciers outside Greenland and Antarctica, 0.60 ± 0.04 mm yr−1 (20 %) from Greenland, 0.19 ± 0.04 mm yr−1 (6 %) from Antarctica, and 0.32 ± 0.10 mm yr−1 (10 %) from changes of land water storage. In the period Jan 2003–Aug 2016 (P2, covered by GRACE and the Argo drifter system), GMSL rise is higher than in P1 at 3.64 ± 0.26 mm yr−1. This is due to an increase of the mass contributions (now about 2.22 ± 0.15 mm yr−1, 61 % of the GMSL trend), with the largest increase contributed from Greenland. The SLB of linear trends is closed for P1 and P2, that is, the GMSL trend agrees with the sum of the steric and mass components within their combined uncertainties. The OMB budget, which can be evaluated only for P2, is also closed, that is, the GRACE-based ocean-mass trend agrees with the sum of assessed mass contributions within uncertainties. Combined uncertainties (1-sigma) of the elements involved in the budgets are between 0.26 and 0.40 mm yr−1, about 10 % of GMSL rise. Interannual variations that overlie the long-term trends are coherently represented by the elements of the SLB and the OMB. Even at the level of monthly anomalies the budgets are closed within uncertainties, while also indicating possible origins of remaining misclosures.

Trends and Uncertainties of Regional Barystatic Sea-level Change in the Satellite Altimetry Era

“…Our total uncertainty in the regional barystatic sea-level trend ranges from 0.62 to 1.02 mm.year −1 for 2003-2016, and from 0.37 to 0.75 mm.year −1 for 1993-2016 for the IMB+WGP combination, with spatial averages of 0.80 and 0.47 mm.year −1 , respectively. While these values may seem large compared to studies focusing on global changes alone (Horwath et al, 2021;Frederikse et al, 2020), other studies also found that regional uncertainties are higher than the previously published global mean rates (Prandi et al, 2021;Bos et al, 2014). For example, in a recent satellite altimetry sea-level change assessment, Prandi et al (2021) found that the local sea-level trend uncertainty due to observational errors (i.e., intrinsic uncertainties) was about two times higher than the global mean sea-level trend uncertainty of Ablain et al (2019).…”

“…Fingerprints of barystatic SLC have been the subject of several studies, ranging from investigating the effects of variations in paleoclimate, for example the SLC due to the last deglaciation event (Lin et al, 2021), to contemporary SLC (Frederikse et al, 2020). Most of the studies including presentday barystatic SLC have focused either on the GRACE satellite period (since 2002) (Bamber and Riva, 2010;Riva et al, 2010;Hsu and Velicogna, 2017;Adhikari et al, 2019;Frederikse et al, 2019), on the closure of the sea-level budget over a longer period (Slangen et al, 2014;Frederikse et al, 2020) or on the barystatic contribution to global mean SLC (Chambers et al, 2007;Horwath et al, 2021). However, an in-depth analysis of regional barystatic SLC and its uncertainties during the satellite altimetry era (since 1993) has not yet been done.…”

“…The importance of quantifying the uncertainties in sea-level studies has increasingly received attention (Bos et al, 2014;Royston et al, 2018;Ablain et al, 2019;Camargo et al, 2020;Palmer et al, 2021;Prandi et al, 2021;Horwath et al, 2021). One of the approaches to describe the uncertainties of a system is to partition the total uncertainty budget into different kinds of uncertainties.…”

Sea-Level Fingerprints Due to Present-Day Water Mass Redistribution in Observed Sea-Level Data

“…In recent years, a number of studies have investigated the closure of the sea-level budget at global and regional scales over the altimetry era [1][2][3][4][5]. This is generally carried out by comparing the altimetry-based sea-level change with the sum of contributions using observations (e.g., Gravity Recovery and Climate Experiment (GRACE) satellite gravimetry data for estimating mass changes, and Argo-based ocean temperature and salinity data) or model outputs (e.g., for estimating glacier mass balance).…”

“…This is generally carried out by comparing the altimetry-based sea-level change with the sum of contributions using observations (e.g., Gravity Recovery and Climate Experiment (GRACE) satellite gravimetry data for estimating mass changes, and Argo-based ocean temperature and salinity data) or model outputs (e.g., for estimating glacier mass balance). Assessing the closure/nonclosure of the sea-level budget has many implications, such as detecting acceleration [2] or an abrupt change in one or several components, for process understanding [5], cross calibrating the different observing systems used to quantify sea-level and its components, detecting possible systematic errors [6,7], placing upper bounds on poorly determined or missing contributions (e.g., from the deep ocean not sampled by Argo [8]), and finally for validating climate models used to simulate future changes. In terms of global average, the sea-level budget is found to be closed up to around 2016 within the observation uncertainties (e.g., [1][2][3][4][5]), although beyond 2016, the global mean budget appears no longer closed [6,7].…”