Greenland Ice Sheet Melting Rapidly From Below

Scientists have uncovered a hidden and alarming process happening deep beneath the ice in the Arctic. New radar data reveals that warming ocean water is aggressively undercutting Greenland’s major glaciers. This bottom-up melting is happening much faster than previous climate models predicted, forcing researchers to rethink how quickly global sea levels could rise in the coming decades.

The Hidden Threat of Ocean Undercutting

For years, scientists focused heavily on the surface melting of the Greenland ice sheet caused by warmer air temperatures. However, recent observations show that the ocean itself is playing a massive role in destroying the ice.

The critical zone is the grounding line. This is the exact point where a glacier leaves the solid bedrock and begins to float on the ocean water. Previously, scientists believed this grounding line was a rigid and mostly stationary boundary. New satellite data shows this is not the case at all.

Instead, the grounding line shifts constantly with the ocean tides. As the tide rises, warm and salty seawater gets pushed miles inland beneath the ice sheet. When the tide falls, the water recedes. Researchers call this process tidal pumping. This constant flushing of warm water creates massive cavities at the base of the glaciers, melting the ice rapidly from the bottom up.

High-Tech Radar Exposes the Damage

This discovery was made possible by advanced satellite technology. Traditional optical satellites cannot see what is happening beneath thousands of feet of ice. To solve this, researchers turned to synthetic aperture radar (SAR).

A team led by scientists from the University of California, Irvine (UCI) and NASA’s Jet Propulsion Laboratory used data from a commercial satellite constellation called ICEye. These small satellites orbit the Earth and bounce radar waves off the surface of the glaciers. By measuring exactly how long it takes the radar signal to return, the satellites can track the tiny vertical movements of the ice surface.

The ICEye data revealed that sections of the ice sheet miles inland were moving up and down in perfect sync with the ocean tides. This vertical movement proved that liquid water had intruded far beneath the solid ice.

This radar data perfectly complements the findings of NASA’s Oceans Melting Greenland (OMG) mission. The OMG mission ran from 2015 to 2021 and involved dropping probes from airplanes into the waters around Greenland. Those probes proved that deep Atlantic water surrounding the island is actually 3 to 4 degrees Celsius warmer than the water near the surface. When this deep, warm water gets pushed under the ice by tidal pumping, it acts like a blowtorch on the base of the glaciers.

Key Glaciers at Immediate Risk

The new radar observations focused heavily on the Petermann Glacier in northwestern Greenland. Petermann is one of the largest and most important glaciers in the region.

The data showed that warm seawater is intruding up to 3.8 miles (about 6 kilometers) beneath the Petermann Glacier’s grounding line. This intrusion is carving a massive cavern into the base of the ice. Scientists estimate the melt rate at the grounding line of the Petermann Glacier is up to 260 feet (80 meters) per year. This rate is nearly double what traditional models predicted.

The 79 North Glacier (Nioghalvfjerdsfjorden) in northeast Greenland is facing a similar fate. As warm Atlantic water pools beneath its massive floating tongue, the ice is thinning from below. If these massive glaciers become unpinned from the bedrock, they will slide into the ocean at a rapidly accelerating pace.

What This Means for Global Sea Levels

The implications of this bottom-up melting are massive for coastal communities around the world. The Greenland ice sheet holds enough frozen water to raise global sea levels by approximately 24 feet (7.4 meters).

Current sea level rise projections from organizations like the Intergovernmental Panel on Climate Change (IPCC) rely on models that treat the grounding line as a fixed point. Because these models do not account for tidal pumping and the deep intrusion of warm water, they likely underestimate the true rate of ice loss.

If major outlets like the Petermann Glacier melt twice as fast as expected, coastal cities from Miami to Mumbai will have significantly less time to prepare for rising tides. Researchers are now working quickly to update global climate models to include this newly discovered undercutting process. The goal is to provide accurate timelines for city planners and governments who need to build sea walls, elevate roads, or relocate vulnerable populations.

Frequently Asked Questions

Why is bottom-up melting faster than surface melting? Ocean water transfers heat much more efficiently than air. The salty, warm water from the Atlantic Ocean gets trapped beneath the ice under high pressure, which lowers the melting point of the ice and causes it to dissolve rapidly.

How much will sea levels rise if the Greenland ice sheet melts? If the entire Greenland ice sheet were to melt completely, global sea levels would rise by about 24 feet (7.4 meters). While this total collapse would take centuries, even a partial melt will cause severe coastal flooding worldwide.

What technology is used to measure this ice melt? Scientists use a combination of tools. They use synthetic aperture radar from satellites like ICEye to measure how the ice moves with the tides. They also use airborne probes from NASA to measure the exact temperature and salinity of the ocean water deep below the surface.

What is a grounding line? A grounding line is the specific boundary where a glacier transitions from resting on solid land to floating on the ocean. The new data shows this line moves back and forth with the tides, allowing warm water to sneak underneath the ice.