An Integrated View of Greenland Ice Sheet Mass Changes Based on Models and Satellite Observations

Abstract

The Greenland ice sheet is a major contributor to sea level rise, adding on average 0.47 ± 0.23 mm year − 1 to global mean sea level between 1991 and 2015. The cryosphere as a whole has contributed around 45% of observed global sea level rise since 1993. Understanding the present-day state of the Greenland ice sheet is therefore vital for understanding the processes controlling the modern-day rates of sea level change and for making projections of sea level rise into the future. Here, we provide an overview of the current state of the mass budget of Greenland based on a diverse range of remote sensing observations to produce the essential climate variables (ECVs) of ice velocity, surface elevation change, grounding line location, calving front location, and gravimetric mass balance as well as numerical modelling that together build a consistent picture of a shrinking ice sheet. We also combine these observations with output from a regional climate model and from an ice sheet model to gain insight into existing biases in ice sheet dynamics and surface mass balance processes. Observations show surface lowering across virtually all regions of the ice sheet and at some locations up to −2.65 m year − 1 between 1995 and 2017 based on radar altimetry analysis. In addition, calving fronts at 28 study sites, representing a sample of typical glaciers, have retreated all around Greenland since the 1990s and in only two out of 28 study locations have they remained stable. During the same period, two of five floating ice shelves have collapsed while the locations of grounding lines at the remaining three floating ice shelves have remained stable over the observation period. In a detailed case study with a fracture model at Petermann glacier, we demonstrate the potential sensitivity of these floating ice shelves to future warming. GRACE gravimetrically-derived mass balance (GMB) data shows that overall Greenland has lost 255 ± 15 Gt year − 1 of ice over the period 2003 to 2016, consistent with that shown by IMBIE and a marked increase compared to a rate of loss of 83 ± 63 Gt year − 1 in the 1993–2003 period. Regional climate model and ice sheet model simulations show that surface mass processes dominate the Greenland ice sheet mass budget over most of the interior. However, in areas of high ice velocity there is a significant contribution to mass loss by ice dynamical processes. Marked differences between models and observations indicate that not all processes are captured accurately within models, indicating areas for future research.

Surface velocity of the Northeast Greenland Ice Stream (NEGIS): assessment of interior velocities derived from satellite data by GPS

“…In the interior, in situ observations of surface movement are sparse and limited to a few locations (e.g., Hvidberg et al, 1997Hvidberg et al, , 2002, and satellite-derived observations of surface velocity and elevation change are limited by their temporal and spatial resolu-tion and the lack of validation data (Joughin et al, 2018a). A small surface thickening has been observed since 1995 from satellite altimetry in the interior, but it is not clear whether it is due to increased precipitation or ice dynamical changes (Mottram et al, 2019). As a result, there is a significant uncertainty in the projections of the future response of the interior areas of the Greenland Ice Sheet to changes at the marine outlet glaciers (Shepherd et al, 2020;Pörtner et al, 2019).…”

“…The mass loss from NEGIS has increased since 2003 (Mouginot et al, 2019). This is mainly due to a rapid retreat of ZI since it lost its floating tongue in 2003 and a slow retreat of NG (Khan et al, 2014;Mouginot et al, 2015), while SG has slowed down after its surge around 1980 . If the marginal loss continues and induces dynamical thinning and acceleration upstream along NEGIS, it could potentially activate the interior parts of NEGIS (Khan et al, 2014;Choi et al, 2017).…”

Subglacial roughness of the Greenland Ice Sheet: relationship with contemporary ice velocity and geology

“…The rate of global sea-level rise contributions from the Greenland Ice Sheet (GrIS) has accelerated over the past 2 decades (Velicogna and Wahr, 2006;Rignot et al, 2011;Mottram et al, 2019); increasing rates of mass loss, driving this acceleration, are partitioned between ice discharge (over the grounding line) and, more recently, enhanced surface melt (Enderlin et al, 2014;van den Broeke et al, 2016Hofer et al, 2017;McMillan et al, 2016;Fettweis et al, 2017;Mouginot et al, 2019;Mottram et al, 2019). To constrain projections for future change, models must parameterise characteristics influencing ice-sheet motion and dynamics (e.g.…”

Improved Ice Velocity Measurements with Sentinel-1 TOPS Interferometry

“…Ice velocity measurements are additionally applied in the evaluation of both surface mass balance (SMB) products and numerical ice sheet models. With more accurate estimates of the interior ice sheet velocity pattern, validation of SMB products and numerical ice sheet models becomes increasingly reliable [14,33,34].…”