Impact of NGGM and MAGIC on Sea Level and Energy Budgets Closure

The SING project aims to evaluate the added value of the NGGM and MAGIC missions for scientific applications and operational services in hydrology, ocean sciences, glaciology, climate sciences, solid earth sciences, and geodesy. Using a closed-loop simulator with a comprehensive description of instrumental, ocean tide, dealiasing and toning errors, synthetic observations of the gravity field have been generated to assess the observability of mass changes occurring in the atmosphere, ocean, hydrosphere, cryosphere, and solid earth for different mission configurations, including GRACE-C-like (single polar pair), NGGM (single inclined pair), and MAGIC (double pair). 

The synthetic gravity observations have first been used to assess the closure of the sea level budget. With historical GRACE, altimetry, and Argo data, global sea level budget closure is achieved with an accuracy of 0.3–0.4 mm/yr (2003–2015). Using VADER-filtered simulations, all three configurations contribute <0.1 mm/yr to the global mean sea level error. NGGM and MAGIC maintain this accuracy even without filtering, unlike GRACE-C. At regional scales, NGGM and MAGIC notably improve significantly the sea level budget closure, especially at seasonal and interannual timescales, though gains for decadal trends remain modest. 

The synthetic gravity observations were also used to assess the closure of the global energy budget. Historical gravimetry, altimetry, and Argo data yield global mean ocean heat uptake (GOHU) accuracy of 0.2–0.3 W/m² (2003-2015). With VADER-filtered simulations, GRACE-C-like missions contribute up to 0.19 W/m² uncertainty, while NGGM and MAGIC improve this by 30–40%, achieving ~0.12–0.13 W/m² accuracy. They also enhance the stability and temporal consistency of GOHU retrievals. Regionally, NGGM and MAGIC outperform GRACE-C by up to 80% in recovering ocean heat content changes at mid-latitudes (30–60° N/S). Slightly better results are obtained with NGGM due to the use of mission error covariance information in the VADER filter. NGGM and MAGIC recover mean and temporal variations in ocean heat uptake at regional scales with up to 50% higher accuracy than GRACE-C.
The NGGM and MAGIC missions will substantially enhance the accuracy, spatial and temporal resolution of gravity-based observations of sea level changes and its drivers. These improvements strengthen global climate assessments, support the evaluation of mitigation policies, and improve climate model validation. In particular, sustained and redundant monitoring of ocean heat uptake would provide an early and robust indicator of changes in radiative forcing, preceding detectable stabilization of global temperatures by several decades. Improved characterization of regional heat-uptake pathways also enhances projections of sea level rise, marine heat extremes, and ocean circulation changes, supporting climate risk management across coastal, marine, and ecosystem applications.