Revisiting the contemporary sea level budget in light of land mass changes and ocean heat uptake.

Balancing the sea level budget requires ocean mass and steric changes to add up to observed total sea level changes. However, both ocean mass and steric changes come with additional constraints: ocean mass changes must be balanced against land mass changes, and global steric changes are directly linked to ocean heat uptake, which is constrained by Earth's energy imbalance (EEI).

We revisit the sea level budget over the GRACE and Argo era (2005-2015), and find an ocean mass change of 1.9 mm/yr, which is consistent with in-situ estimates of land mass loss due to hydrology and ice mass loss from glaciers and ice sheets. We find an upper-ocean (0-2000m) steric change of 1.2 mm/yr, which agrees well with EEI estimates. To obtain the total sea-level change, we combine satellite altimetry with seafloor deformation estimates from an ensemble of GIA predictions and GRACE, which yields a total sea-level rise of 3.8 mm/yr over the GRACE-Argo period. This results in a budget deficit of 0.7 [95% confidence interval: 0.2-1.2] mm/yr.

Attributing this deficit to deep steric expansion that is missed by the GRACE+Argo approach, is incompatible with both in-situ estimates of deep-ocean warming and with modelled and observed estimates of EEI. Attributing this discrepancy to an underestimation of ocean mass change would require a substantial revision of land-water storage or ice-mass loss estimates.

This budget imbalance can be almost fully attributed to the Indian Ocean, while in all other basins, the budget is balanced well within confidence intervals. The Indian Ocean is not a region known for substantial deep convection, which effectively rules out that deep ocean heat uptake is responsible for the deficit.

The imbalance shows that our current estimates of sea-level rise and its contributors are not yet fully consistent and one or more components need a revision.