Since June, 2018, the Gravity Recovery and Climate Experiment Follow‐On (GRACE‐FO) is extending the 15‐year monthly mass change record of the GRACE mission, which ended in June 2017. The GRACE‐FO instrument and flight system performance has improved over GRACE. Better attitude solutions and enhanced pointing performance result in reduced fuel consumption and gravity range rate post‐fit residuals. One accelerometer requires additional calibrations due to unexpected measurement noise. The GRACE‐FO gravity and mass change fields from June 2018 through December 2019 continue the GRACE record at an equivalent precision and spatiotemporal sampling. During this period, GRACE‐FO observed large interannual terrestrial water variations associated with excess rainfall (Central US, Middle East), drought (Europe, Australia), and ice melt (Greenland). These observations are consistent with independent mass change estimates, providing high confidence that no intermission biases exist from GRACE to GRACE‐FO, despite the 11‐month gap. GRACE‐FO has also successfully demonstrated satellite‐to‐satellite laser ranging interferometry.

Ice losses from the Greenland and Antarctic ice sheets have accelerated since the 1990s, accounting for a significant increase in the global mean sea level. Here, we present a new 29-year record of ice sheet mass balance from 1992 to 2020 from the Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE). We compare and combine 50 independent estimates of ice sheet mass balance derived from satellite observations of temporal changes in ice sheet flow, in ice sheet volume, and in Earth's gravity field. Between 1992 and 2020, the ice sheets contributed 21.0±1.9 mm to global mean sea level, with the rate of mass loss rising from 105 Gt yr ⁻¹ between 1992 and 1996 to 372 Gt yr ⁻¹ between 2016 and 2020. In Greenland, the rate of mass loss is 169±9 Gt yr ⁻¹ between 1992 and 2020, but there are large inter-annual variations in mass balance, with mass loss ranging from 86 Gt yr ⁻¹ in 2017 to 444 Gt yr ⁻¹ in 2019 due to large variability in surface mass balance. In Antarctica, ice losses continue to be dominated by mass loss from West Antarctica (82±9 Gt yr ⁻¹ ) and, to a lesser extent, from the Antarctic Peninsula (13±5 Gt yr ⁻¹ ). East Antarctica remains close to a state of balance, with a small gain of 3±15 Gt yr ⁻¹ , but is the most uncertain component of Antarctica's mass balance. The dataset is publicly available at https://doi.org/10.5285/77B64C55-7166-4A06-9DEF-2E400398E452 (IMBIE Team, 2021).

We have determined the ice mass evolution of the Antarctic and Greenland ice sheets (AIS and GIS) and Gulf of Alaska (GOA) glaciers from a new GRACE global solution of equal-area surface mass concentration parcels (mascons) in equivalent height of water. The mascons were estimated directly from the reduction of the inter-satellite K-band range-rate (KBRR) observations, taking into account the full noise covariance, and formally iterating the solution. The new solution increases signal recovery while reducing the GRACE KBRR observation residuals. The mascons were estimated with 10 day and 1 arcdeg equal-area sampling, applying anisotropic constraints. An ensemble empirical mode decomposition adaptive filter was applied to the mascon time series to compute annual mass balances. The details and causes of the spatial and temporal variability of the land-ice regions studied are discussed. The estimated mass trend over the total GIS, AIS and GOA glaciers for the time period 1 December 2003 to 1 December 2010 is −380 ± 31 Gt a⁻¹, equivalent to −1.05 ± 0.09 mm a⁻¹ sea-level rise. Over the same time period we estimate the mass acceleration to be −41 ± 27 Gt a⁻² , equivalent to a −0.11 ± 0.08 mm a⁻² sea-level acceleration. The trends and accelerations are dependent on significant seasonal and annual balance anomalies.

Satellite laser ranging (SLR) observations have long been relied upon for measuring changes in Earth's dynamic oblateness, C₂₀. This major component of Earth's time‐variable gravity field is not well‐observed by the GRACE and GRACE‐FO missions, leading to the common practice of replacing their values with those obtained by SLR. The C₃₀ coefficient, which has a large impact on the recovered Antarctic Ice Sheet mass changes, is shown here to be poorly observed by GRACE/GRACE‐FO when either mission is operating without two fully functional accelerometers. The GRACE spacecraft pair operated nominally until October 2016 when one accelerometer was powered off due to battery limitations, while GRACE‐FO is currently excluding one accelerometer from the data processing due to elevated noise levels. Beginning with the launch of LARES in 2012, SLR‐derived C₃₀ values are suitable for replacing any problematic GRACE/GRACE‐FO estimates, enabling the accurate recovery of Antarctic Ice Sheet mass changes, among others.

We have derived a gravity field solution in spherical harmonics to degree and order 900, GRGM900C, from the tracking data of the Gravity Recovery and Interior Laboratory (GRAIL) Primary (1 March to 29 May 2012) and Extended Missions (30 August to 14 December 2012). A power law constraint of 3.6 ×10⁻⁴/ℓ² was applied only for degree ℓ greater than 600. The model produces global correlations of gravity, and gravity predicted from lunar topography of ≥ 0.98 through degree 638. The model's degree strength varies from a minimum of 575–675 over the central nearside and farside to 900 over the polar regions. The model fits the Extended Mission Ka‐Band Range Rate data through 17 November 2012 at 0.13 μm/s RMS, whereas the last month of Ka‐Band Range‐Rate data obtained from altitudes of 2–10 km fit at 0.98 μm/s RMS, indicating that there is still signal inherent in the tracking data beyond degree 900.