New study shows how atmospheric warming could weaken polar ice shelves

New research provides deep insight into how subglacial discharge in Greenland can significantly boost melting at the base of ice shelves, deepening scientists’ understanding of the role of surface melt runoff in the melting of polar ice shelves.

The findings are based on high-resolution modelling by an international team of researchers including Tore Hattermann from the iC3 Polar Research Hub in Tromsø. The study focuses on the Petermann Ice Shelf, a floating extension of a glacier pushing into the sea.

Like other ice shelves, the Petermann Ice Shelf acts as a brake on the land-based glacier behind it. If the ice shelf thins or breaks up, the glacier’s movement could speed up, accelerating global sea level rise.

A shift in how melting happens

Using a detailed 3-D model of the Petermann Ice Shelf and fjord, the team simulated different climate scenarios. They found that when subglacial discharge is low or absent, heat is carried beneath the ice mainly by slow-moving ocean currents. As discharge increases, extra energy for basal melting no longer comes from ocean heat, but from turbulence generated by fast-flowing meltwater.

Figure: A graphical summary of the results showing basal melt rate (m_b), and its drivers, namely, thermal driving (ΔT) and friction velocity (u^*). The discharge type categories correspond to the experiment design. Modified from Prakash et al. (2025). Nat Commun 16, 4213 (2025).

“This marks a regime change,” explains Tore. “Once subglacial discharge passes a certain level, basal melt is limited not by ocean heat but by how quickly that heat can be transferred to the ice—and the meltwater flow speeds that up.” 

Tore adds that:

“The coupling between surface melt runoff and enhanced ocean-heat driven melting is well established. Hence, our study does not challenge that paradigm. Rather, it adds insight into how this mechanism works, simulating it with an unprecedented level of detail.”

In the model, turbulent mixing concentrates in long, narrow channels at the ice shelf’s base, creating areas of high shear stress and melt rates of up to 180 metres per year—seven times higher than under ocean-only melt conditions.

Modelling future scenarios

The researchers ran model experiments under a high-emissions scenario. They found that even if ocean warming levels off, continued atmospheric warming would increase subglacial discharge and accelerate melting. 

Even without significant ocean warming, through this mechanism of enhanced meltwater runoff, basal channels could cut through the ice shelf within a decade and compromise its integrity. This weakening would reduce resistance to inland ice flow, leading to faster glacier movement and more sea-level rise.

Why this matters

Petermann is one of the last remaining floating ice tongues in northern Greenland. Its location makes it crucial for regulating ice flow from a Greenland ice sheet sector that holds enough ice to raise sea levels by an additional four metres.

Previous studies focused mainly on ocean temperatures when assessing ice shelf vulnerability. This research shows that atmospheric warming—and its effect on summer meltwater runoff—may pose an even more immediate threat. 

The findings from Greenland also have implications for Antarctic ice shelves. Many of these feature similar channel systems. While Antarctic surface melting is limited today, ice sheets there may experience enhanced discharge-driven melt in a warming world. 

Understanding how meltwater interacts with ice shelf geometry is critical for projecting future sea-level rise.

About the paper and the authors

The study “Enhanced subglacial discharge amplifies Petermann Ice Shelf melting when ocean thermal forcing saturates” was published in Nature Communications and is available open access.

Lead author Abhay Prakash is a postdoctoral researcher at Stockholm University. iC3 Polar Research Hub’s Tore Hattermann contributed to the study. 

Tore is a researcher at the Norwegian Polar Institute and at the Department of Geosciences at UiT The Arctic University of Norway. His research focuses on ocean-ice interactions in polar regions. He is particularly interested in how physical processes in the ocean regulate the heat transport toward and affect the ice shelf stability and sea-level rise.

Note: A previous iC3 blog with the title “New study suggests that atmospheric warming could significantly weaken polar ice shelves” that summarised this study contained mistakes and has been deleted. The iC3 communications team apologises for any inconvenience caused.