Tyler Sutterley

We report on the ice mass loss of the Antarctic and Greenland Icesheets and of the world Glaciers and ice caps from 2002 to 2026 using data from the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO) missions.In Greenland, we detect a slowdown in ice mass loss since 2012 due to lower melt runoff production caused by a succession of colder summers, especially in the southwest and northeast sectors. The mass loss averages 245+/-47 Gt/year for the period 2002-2026 with the acceleration in loss negligible after 2012 due to reduced surface melt, especially in the southwest and northeast. A disproportionate portion of the mass loss is driven by North Greenland which includes the two largest marine-based basins, which are most prone to rapid sea level rise.In Antarctica, we detect a slowdown in ice mass loss in 2019-2024 which was caused by an increase in accumulation of snowfall, especially in Queen Maud Land, which is unprecedented in the GRACE record. Increase in snowfall is also observed in Totem and Moscow and Wilkins land East Antarctica and in the Antarctic Peninsula. This short-lived mass gain in 2019-2024 mirrors a similar episode in 2004–2007 both in magnitude and duration, reflecting interannual variability in surface mass balance, not a reversal of long-term trends. A disproportionate portion of the mass loss is controlled by the Amundsen Sea Embayment of West Antarctica and to a lesser extent by the Wilkes Land sector of East Antarctica. Both ice sheets continue to lose ice, with no statistically significant acceleration during the GRACE era, confirming that Antarctica’s apparent recovery is a brief snowfall-driven pause within a persistent long-term decline.For the world Glacial and Ice Caps (GIC) we find a sustained mass loss of 296+/-30 Gt/year and an acceleration in mass loss of 6+/-2 Gt/year^2, the Arctic is still dominating the GIC mass loss signal and account for 71% of the total GIC mass loss. Ice sheet and Glaciers continue to have a major impact on sea level rise, the ice sheets show a relative loss in acceleration after 2012, but the longer record 1979-2025 shows an acceleration in mass loss.

We look to understand how uncertainties in atmospheric pressure affect the precision of Antarctic ice sheet mass balance estimates derived from time-variable gravity measurements using an ensemble of reanalysis outputs along with in-situ observations of surface pressure. Before the formulation of monthly spherical harmonic gravitational fields from GRACE and GRACE Follow-On, sub-monthly atmospheric variations are removed using the "de-aliasing" products computed from ERA reanalyses and ECMWF operational forecasts and processed by the German Research Centre for Geosciences (GFZ). While this helps remove the majority of the atmospheric signal globally, the quality of atmospheric forecasts and analyses is typically lower over Antarctica due to the scarcity of available data and the strong topographic contrasts. As uncertainties in the dealiasing fields directly map into errors in the spherical harmonic fields, improving the characterization of atmospheric circulation over the poles will help improve the month-by-month precision of Antarctic mass change estimates. Here, we estimate the impacts of atmospheric pressure uncertainty on ice sheet mass balance at both continental and regional scales using four independently derived reanalyses (ERA5, MERRA-2, JRA-3Q, and NCEP-CFSR). We find that equivalent atmospheric pressure uncertainties of 1 millibar over the entirety of Antarctica will result in a mass uncertainty of over 100 gigatonnes. From our reanalysis ensemble, we find average monthly uncertainties of 0.6–1.1 millibars (71–132 gigatonnes) over the continent, likely limiting our present-day mass change estimates over short timescales. Additionally, we calculate the atmospheric loading effects in Antarctica under different scenarios related to the structure of the Earth's atmosphere and Earth's geometry. We find that for the purposes of deriving atmospheric pressure uncertainties, simple two-dimensional formulations are likely adequate.

NASA’s ICESat-2 mission was launched in 2018, carrying a photon-counting laser altimeter, with a primary objective of measuring height changes across Earth’s surface. ICESat-2 has provided measurements of ice surface height between 88º N and S, repeated four times per year, with high vertical accuracy and along-track spatial resolution. Its accuracy and coverage has enabled near-complete recovery of height changes across the ice sheets, capturing subtle changes in the interior, and rapid changes along the dynamic margins with steep slopes and the floating peripheral ice shelves. The ICESat-2 Science Team has developed a suite of algorithms that produce along-track and gridded land ice height products at various levels of processing, all freely available at the National Snow and Ice Data Center. Here, we describe three higher-level land-ice data products derived from ATL06 and their underlying algorithms: along-track height change (ATL11), digital elevation model (ATL14) and gridded surface height change (ATL15). We demonstrate the suitability of each data product for studying different ice sheet regions. We then show height changes for Greenland and Antarctica from ATL15 during the first 6 years of the ICESat-2 mission (October 2018–December 2024), illustrating how ICESat-2 measurements can distinguish the multi-year trends from seasonal fluctuations.

The eo-tides package provides powerful parallelised tools for integrating satellite Earth observation (EO) data with ocean tide modelling. The package provides a flexible Python toolkit for attributing modelled tide heights to a time-series of satellite images based on the spatial extent and acquisition time of each satellite observation (Figure 1).

The process of laser light reflecting from surfaces made of scattering materials that do not strongly absorb at the wavelength of the laser can involve reflections from hundreds or thousands of individual grains, which can introduce delays in the time between light entering and leaving the surface. These time-of-flight biases depend on the grain size and density of the medium, and thus they can result in spatially and temporally varying surface height biases estimated from laser altimeters, such as NASA's ICESat-2 (Ice Cloud, and land Elevation Satellite-2) mission. Modeling suggests that ICESat-2 might experience a bias difference as large as 0.1–0.2 m between coarse-grained melting snow and fine-grained wintertime snow (Smith et al., 2018), which exceeds the mission's requirement to measure seasonal height differences to an accuracy better than 0.1 m (Markus et al., 2017). In this study, we investigate these biases using a model of subsurface scattering, laser altimetry measurements from NASA's ATM (Airborne Topographic Mapper) system, and grain size estimates based on optical imagery of the ice sheet. We demonstrate that distortions in the shapes of waveforms measured using ATM are related to the optical grain size of the surface estimated using optical reflectance measurements and show that they can be used to estimate an effective grain radius for the surface. Using this effective grain radius as a proxy for the severity of subsurface scattering, we use our model with grain size estimates from optical imagery to simulate corrections for biases in ICESat-2 data due to subsurface scattering and demonstrate that, on the basis of large-scale averages, the corrections calculated based on the satellite optical imagery match the biases in the data. This work demonstrates that waveform-based altimetry data can measure the optical properties of granular surfaces and that corrections based on optical grain size estimates can correct for subsurface-scattering biases in ICESat-2 data.

Consensus from mass balance studies published in the past decade revealed an increase in mass loss from the Antarctic Ice Sheet. However, independent methods (e.g., gravity, altimetry, and mass budget) for determining the rate of mass loss disagree about the magnitude and uncertainty of estimates for East Antarctica. This discrepancy is largely due to the size of East Antarctica, the low signal-to-noise ratios of existing sensors, and the confluence of uncertainties for each method. As a result, ice sheet models may not be well-constrained to make future projections of ice mass change and sea level change. Here, we combine GRACE/GRACE-FO, ICESat/ICESat-2, and GPS observations and extend Velicogna et al. (2002) iterative algorithm to improve the estimate of the Antarctic mass balance. We add outputs from surface mass balance (SMB) and firn models to satellite altimetry, time-variable gravity, and GPS measurements. We evaluate the sensitivity of the approach to realistic ice mass spatial and time distributions using an effective density map derived from ICESat-2 data, and reconstructions of SMB and firn depth from climate model outputs. Our result provides information on how the GPS network could be completed to resolve major uncertainties, obtain a better glacial isostatic adjustment (GIA), and a better estimate of ice mass balance.

The recent Ice sheet Mass Balance Inter-comparison Exercise (IMBIE) suggests that between 2012 and 2017 the East Antarctic Ice Sheet was approximately in balance, experiencing a rate of mass change of 23 ± 38 Gt yr-1. While this study provided an important statistical reconciliation of various studies across several techniques, the root cause of the differences amongst the estimates remains unresolved. Satellite gravimetry provides a direct measurement of mass change; however, it is sensitive to all mass changes, and the necessary corrections for solid earth changes are substantial and poorly constrained. Satellite altimetry provides measurements of volume change, which includes changes in ice mass and non-ice mass. The latter is largely driven by changes in the density of the snow and firn requiring poorly constrained models for conversion to mass. Here, rather than deriving ice-sheet mass balance using a single technique, we use both satellite gravimetry and altimetry to better: (1) reconcile mass balance estimates between the two techniques, (2) improve constraint on firn dynamics, and (3) attempt to partition the driver of change. Because these two measurements are sensitive to different processes, using them in conjunction provides additional constraint of the most unknown processes.Our new technique solves for the change in total firn air content through time for the entire Antarctic Ice Sheet that provides a best-fit mass solution between altimetry and gravimetry. In such a way, we produce ice-sheet mass change at the fine-scale resolution of ice elevation measurements (10 km) that best matches the coarsely resolved (>100km) mass change from gravimetry. Our results indicate that during the ICESat-2 era (April 2019 through June 2023), the East Antarctic Ice Sheet gained mass at a rate of 160 Gt yr-1, three times the average mass gain over the two decades prior (52 Gt yr-1). The sector that spans 60E to 130E received the largest anomalous gains in mass (precipitation). These gains, in conjunction with minor gains from the Antarctic Peninsula (23 Gt yr-1), fully balance the continued mass losses from West Antarctica (-139 Gt yr-1). Large precipitation events over both East Antarctica and the Antarctic Peninsula are driving the mass gains; however, more time is needed to determine whether these changes are long-term or only short-lived given the ICESat-2 time series is just over 4 years in length. These results suggest that atmospheric dynamics play a key role in driving the mass balance of the East Antarctic Ice Sheet and have potential to rapidly change the overall mass balance of the ice sheet.

The ongoing deceleration of Whillans Ice Stream, West Antarctica, provides an opportunity to investigate the role of grounded ice flux in downstream pinning point evolution on decadal time scales. Here, we construct and analyze a 20-year, multi-mission satellite altimetry record of dynamic ice surface-elevation change (dh/dt) in the grounded region between lower Whillans Ice Stream and Crary Ice Rise, a major Ross Ice Shelf pinning point. We developed a new method for generating multi-mission time series that reduces spatial bias and implemented this method with altimetry data from the Ice, Cloud, and land Elevation Satellite (ICESat; 2003–09), CryoSat-2 (2010–present), and ICESat-2 (2018–present) altimetry missions. We then used the 20-year dh/dt time series to identify persistent patterns of surface elevation change and to evaluate regional mass balance. Our results suggest that changes in ice flux associated with Whillans Ice Stream stagnation drive non-linear mass change responses isolated to the Crary Ice Rise region, producing persistent, spatially heterogeneous thickness changes. The resulting mass redistribution modifies the grounding zone and mass balance of the Crary Ice Rise region, in turn adjusting the buttressing regime of the southern Ross Ice Shelf embayment.

The ongoing deceleration of Whillans Ice Stream, West Antarctica, provides an opportunity to investigate the co-evolution of ice-shelf pinning points and ice-stream flux variability. Here, we construct and analyze a 20-year multi-mission satellite altimetry record of dynamic ice surface-elevation change (dh/dt) in the grounded region encompassing lower Whillans Ice Stream and Crary Ice Rise, a major pinning point of Ross Ice Shelf. We developed a new method for generating multi-mission time series that reduces spatial bias and implemented this method with altimetry data from the Ice, Cloud, and land Elevation Satellite (ICESat; 2003–09), CryoSat-2 (2010–present), and ICESat-2 (2018–present) altimetry missions. We then used the dh/dt time series to identify persistent patterns of surface-elevation change and evaluate regional mass balance. Our results suggest a persistent anomalous reduction in ice thickness and effective backstress in the peninsula connecting Whillans Ice Plain to Crary Ice Rise. The multi-decadal observational record of pinning-point mass redistribution and grounding zone retreat presented in this study highlights the on-going reorganization of the southern Ross Ice Shelf embayment buttressing regime in response to ice-stream deceleration.