📄 earth_science

Greenland Ice Sheet to fall below its Holocene minimum size by 2300

This study presents robust simulations indicating that under current warming trajectories, the Greenland Ice Sheet will shrink below its Holocene minimum size by 2300 CE, contributing 26–86 cm to sea-level rise, whereas substantial emissions reductions could limit this contribution to approximately 10 cm.

Original authors: Joshua Cuzzone, Jason Briner, Gerard Otiniano, Olivia Truax, Elizabeth Thomas, Eric Steig, Gregory Hakim, Joseph Tulenko, Mathieu Morlighem, Nicole-Jeanne Schlegel, Sophie Nowicki, Sudip Acharya, Jaco

Published 2026-06-29

📖 5 min read🧠 Deep dive

CC BY 4.0

Original authors: Joshua Cuzzone, Jason Briner, Gerard Otiniano, Olivia Truax, Elizabeth Thomas, Eric Steig, Gregory Hakim, Joseph Tulenko, Mathieu Morlighem, Nicole-Jeanne Schlegel, Sophie Nowicki, Sudip Acharya, Jacob Anderson, Lambert Caron, Anne de Vernal, Jacob Downs, Emilie Folie-Boivin, Ryan Fleetwood, Holly Kyeore Han, Jesse Johnson, Eric Larour, Ana Carolina Luzardi, Zilu Meng, Karlee Prince, Joerg Schaefer, Margie Turin, Liza Wilson, Xiner Wu, Nicolas Young

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

The Big Picture: A Giant Ice Block on a Hot Stove

Imagine the Greenland Ice Sheet as a massive, ancient block of ice sitting on a stove. For the last 11,500 years (a period scientists call the Holocene), the stove has been turned on and off a few times, but it has never been hot enough to melt the block down to its absolute smallest size since the last time the Earth was really warm (about 125,000 years ago).

This new study acts like a time machine and a crystal ball combined. The researchers built a super-computer simulation to see how that ice block reacted to past warmth and to predict what will happen if we keep turning up the heat today.

1. The "Test Drive" (Checking the Model)

Before they could trust their predictions for the future, they had to make sure their computer model was accurate. They ran a "test drive" using the last 11,500 years of history.

The Challenge: Previous computer models were like bad GPS systems; they couldn't quite match the real-world evidence (like ancient rocks and sea levels) showing how much the ice shrank in the past.
The Fix: The team improved their model by adding more realistic details, such as how the ocean melts the ice from underneath and how the ice cracks and calves (breaks off).
The Result: They ran 20 different versions of the past. Six of these versions matched the geological evidence perfectly. They used these six "best drivers" to create a reliable baseline for the future.

2. The Past: A Temporary Retreat

During the warmest part of the Holocene (about 11,000 to 6,000 years ago), the ice sheet did shrink.

The Analogy: Think of it like a snowman on a sunny day. It lost some weight and got smaller, especially around the edges (the "ablation zone").
The Limit: However, even at its smallest, the ice sheet stayed within a "comfort zone." It shrank, but it didn't disappear, and it eventually grew back a bit as things cooled down. The ice sheet was stable, just smaller than it is today.

3. The Future: Turning the Heat Up to "High"

The researchers then asked: What happens if we keep warming the planet at our current rate?

They tested four different scenarios, ranging from "we fix the problem quickly" to "we keep burning fossil fuels as much as possible."

The "Good" Scenario (Low Emissions): If we drastically cut emissions, the ice sheet loses a little bit of mass (about 10 cm of sea-level rise), but it stays within the range of what happened in the past. It's like the snowman losing a few inches of snow but staying intact.
The "Bad" Scenarios (Current Trajectory & High Emissions): If we continue on our current path or burn more fossil fuels, the ice sheet enters uncharted territory.
- The Tipping Point: The study predicts that by the year 2300, the Greenland Ice Sheet will shrink to a size smaller than it has been at any point in the last 11,500 years.
- The Non-Linear Explosion: This is the most critical part. The melting doesn't just speed up linearly; it explodes. As the ice gets smaller, the "melting zone" (where the ice turns to water) moves inland and up the mountains.
- The Analogy: Imagine a bathtub with a hole in the bottom. At first, the water leaks out slowly. But as the water level drops, the hole gets bigger relative to the water, and the drain opens wider. The ice sheet is hitting a point where melting feeds more melting.

4. The Consequences: A New Reality

If the ice sheet shrinks below its Holocene minimum, it means we are breaking a 11,500-year record.

Sea Level Rise: Under current warming paths, this shrinking ice sheet will add between 26 and 86 centimeters (about 1 to 3 feet) to global sea levels by 2300. If we go with the worst-case scenario, it could add up to 1.4 meters (nearly 5 feet).
The "Camp Century" Example: The paper mentions a specific location called Camp Century, which used to be buried deep in the ice where it was safe and cold. By 2200, under current warming, this spot will be in the "melting zone," meaning the ice there will be melting away toward the surface.

The Bottom Line

The paper concludes that the Greenland Ice Sheet is currently stable within the bounds of the last 11,500 years. However, if we continue with our current warming trajectory, we will push the ice sheet past that boundary. It will become smaller than it has been since the last major warm period 125,000 years ago, leading to a rapid, self-sustaining loss of ice that our planet hasn't seen in a very long time.

The only way to stop this from happening is to drastically reduce emissions, which would keep the ice sheet's size within the "safe" historical range.

Problem Statement
The long-term response of the Greenland Ice Sheet (GrIS) to sustained warmth remains a fundamental uncertainty in climate science. While satellite observations capture accelerating mass imbalance over the last quarter-century, they are insufficient for evaluating centennial- to millennial-scale trajectories. The Holocene (approximately the last 11,700 years) represents the most recent geological interval where the GrIS experienced centuries of regional summer temperatures 2–5°C above pre-industrial levels, offering a natural benchmark for assessing ice-sheet sensitivity. However, previous ice-sheet models have struggled to reproduce the geologically constrained evolution of the GrIS throughout the Holocene, often underestimating the magnitude and persistence of ice loss. Furthermore, it remains unresolved whether the GrIS as a whole can reproduce these past changes and how future evolution under various warming scenarios compares to the full range of Holocene variability.

Methodology
To address these gaps, the authors employed the Ice-sheet and Sea-level System Model (ISSM) to simulate GrIS evolution from 12.5 ka (early Holocene) through 2300 CE. The study utilized a multidisciplinary, data-constrained approach:

Model Initialization and Physics: The model was initialized using the reconstructed early Holocene ice extent (12.5 ka) from PaleoGrIS. The simulations incorporated physically based parameterizations for ice–ocean interactions, including submarine melting beneath floating ice and calving at marine termini. The model accounted for glacial isostatic adjustment (GIA) by prescribing bedrock vertical motion and sea-level changes based on global GIA reconstructions, though GIA was not simulated transiently.
Climate Forcing:
- Holocene (12.5 ka – 1850 CE): An ensemble of 20 simulations was driven by an expanded range of paleoclimate reconstructions. These included four distinct temperature reconstructions (derived from ice-core $\delta^{15}$ N, data-assimilation with ice cores, and marine proxies) and two precipitation scenarios.
- Historical and Future (1850 – 2300 CE): Simulations were forced by output from the CMIP6 NCAR CESM2-WACCM model. This covered four Shared Socioeconomic Pathways (SSPs): SSP1-2.6 (high mitigation), SSP2-4.5 and SSP3-7.0 (intermediate), and SSP5-8.5 (fossil-fuel intensive). For scenarios extending only to 2100, a pattern-scaling approach was used to extend anomalies to 2300 CE while preserving spatial structures.
Data-Model Comparison (DMC): To evaluate model skill, the authors applied seven independent criteria against geological observations. These criteria included ice-margin reconstructions, paleoclimate proxy constraints, minimum extent, re-expansion patterns, and specific regional histories (e.g., Prudhoe Dome deglaciation). Six ensemble members were selected as the "best runs" based on their fit to these benchmarks.

Key Results

Holocene Reconstruction: The validated ensemble successfully reproduced the Holocene evolution of the GrIS, capturing a period of smaller-than-present ice area. The simulations indicate that peak Holocene mass loss rates (~3–4 $\times$ 10 $^4$ Gt century $^{-1}$ ) occurred between 11.6 and 8 ka, with a pronounced spatial shift from northern basins in the early Holocene to western basins in the late Holocene.
Future Trajectories:
- Under current warming trajectories (intermediate SSPs), the GrIS is projected to shrink below its Holocene minimum extent and volume by 2300 CE.
- Mass loss rates under high-emission scenarios (SSP5-8.5) accelerate non-linearly, reaching ~24.7 $\times$ 10 $^4$ Gt century $^{-1}$ by 2300 CE—tenfold the maximum rates observed during the Holocene.
- The fraction of the ice sheet subject to ablation (melting) increases non-linearly as the Equilibrium Line Altitude (ELA) rises, driven by surface-mass-balance–elevation feedbacks. By 2050 CE, under current trajectories, the ablation zone will reach unprecedented levels relative to the Holocene.
Sea-Level Contribution: By 2300 CE, the GrIS is projected to contribute 26–86 cm of sea-level equivalent (SLE) under intermediate scenarios. Under the high-emission SSP5-8.5 scenario, this contribution could reach ~1.4 m (19% of current volume). Conversely, limiting warming to SSP1-2.6 restricts the contribution to approximately 10 cm.
State Change: The simulations suggest the GrIS is approaching a fundamental state change. Unlike the Holocene, where the ablation zone was confined to marginal regions, future warming drives the ablation zone inland and to higher elevations. For instance, the Camp Century site, currently in the accumulation zone, is projected to enter the ablation zone by 2200 CE under intermediate trajectories.

Significance and Claims
The paper claims to provide the most robust, data-validated estimates of GrIS evolution spanning the Holocene to the year 2300. By resolving the mismatch between previous models and geological constraints, the study establishes a foundation for projecting future ice-sheet commitment. The authors assert that future warming may push the Greenland Ice Sheet beyond the range of states experienced during the Holocene, potentially entering a state of sustained and self-amplifying mass loss. The results highlight that while substantial emissions reductions can limit the GrIS contribution to sea-level rise to ~~10 cm, current trajectories risk driving the ice sheet to its smallest size since the last interglacial optimum (~~125,000 years ago), with mass loss rates exceeding any recorded in the geological past.