Greenland ice sheet could fully melt after reaching specific tipping point, study finds

Greenland’s ice sheet currently spans over 1.7 million square kilometers and is the largest freshwater reservoir in the northern hemisphere. The ice sheet has already lost over a trillion tonnes of its total mass since the 1980s, with melting rates six times higher in the last decade. Indeed, a recent study found that an average of 30 million tonnes of ice is now being lost every hour.

Continued melting of the ice sheet from a warmer atmosphere and surrounding ocean causes both sea level rise and changes in the salinity of the ocean. This can have significant impacts on the immediate marine ecosystem, but also globally, as sea level increases pose challenges for coastal communities—predictions have suggested a rise of 7 meters if the entire ice sheet melts.

New research, published in The Cryosphere, has identified the tipping point at which the loss of ice mass may be too stark for the ice sheet to recover, potentially leading to complete melting. To do so, Dr. Michele Petrini of Norway’s Bjerknes Centre for Climate Research and colleagues assessed the surface mass balance of Greenland’s ice sheet, referencing the difference between snow accumulation and loss due to melting.

The researchers used modeling to simulate the impact of different climates on the surface mass balance. They found that when approximately 230 gigatons of ice is lost in a single year, corresponding to 60% of the surface mass balance compared to pre-industrial times, then this is the pivotal tipping point that could initiate a relatively rapid descent (geologically speaking, at 8–40,000 years) into complete loss of the Greenland ice sheet.

This corresponds to a global mean temperature increase of 3.4°C. For context, in 2024, global mean temperature reached 1.5°C above pre-Industrial levels, the first time the planet has exceeded this important threshold set by the 2015 Paris Agreement to limit the impacts of climate change.

Dr. Petrini and the team identified elevation, due to topography, as a key influence on the surface mass balance, with ice sheets retreating until remnant pockets remain as ice caps on high elevation areas. In particular, glacial isostatic adjustment is an important factor, as when ice sheets melt and reduce the weight on the underlying bedrock, the land begins to rise over centuries to millennia.

When the ice sheet surface is lowered by melting at a rate outweighing the uplift of the landscape due to glacial isostatic adjustment, then the Greenland ice sheet mass tips from approximately 50% ice mass loss to nearly complete melting. This negative surface mass balance could last for thousands of years.

As the century continues, loss of ice from surface melting is likely to outweigh that from the ice sheet margins extending into a warming ocean as the margins retreat inland. Ice loss would then be further exacerbated by surface albedo feedbacks, whereby less ice means there is reduced “white” surface to reflect incoming solar radiation out to space, meaning it is instead absorbed by the comparatively “dark” land and ocean, warming the ambient environment and causing more melting, creating a positive feedback loop.

Crucially, the researchers identified a portion of the Greenland ice sheet to the west that may play a large role in determining the final state of the ice sheet. When this western margin remains in a coastal region with high topography, there is minimal ice loss to the north and south. However, as this western margin loses its coastal connection, the Greenland ice sheet retreats eastwards and could result in over 80% mass loss.

In fact, simulations have shown that the ice sheet may have benefitted from elevated western topography and ice caps during the last interglacial 130–115,000 years ago, preventing total ice sheet loss. Consequently, this may be a pocket of the ice sheet offering hope for the future. For as long as we can maintain a substantial ice presence on this coastal western margin, the current Greenland ice sheet may be stabilized enough to not pass the threshold for complete melting.

This work is caveated by the fact the researchers do not include ice-atmosphere feedback in their modeling, whereby the inland retreat may increase cloud cover and therefore precipitation over the ice sheet interior to cause thickening. Yet, they state that they do not believe this would drastically change their results, with isostatic rebound having a greater effect.

Therefore, they ultimately warn that anthropogenic climate change is undoubtedly pushing us closer to this, and other, tipping points across the planet. As a result, it is imperative to continue efforts to tackle climate change so that temperature thresholds are not exceeded further.

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