Climate change would be much worse without the oceans, which have absorbed 90 percent of the excess heat humanity has released into the atmosphere. This warming of the oceans has already been devastating for organisms who live there, but it also comes back to bite us in a more unexpected way: it contributes to the destruction of the seated ice up from Greenland.
This diseased ice sheet (the part that sits on land) contributed to more than 17% of the sea level rise observed between 2006 and 2018, and new research delivers even more worrying news. (Greenland has much less ice than Antarctica but is losing 270 billion tonnes per year, compared to Antarctica’s 150 billion tons.) Northern Greenland’s ice shelves – ice that floats on the ocean instead of resting on land – have actually lost more than a third of their volume since 1978, thanks to the absorption of warm sea water. away from their stomach. Three of these northern ice shelves have completely collapsed since 2000, and the remaining five are rapidly deteriorating, in turn destabilizing neighboring glaciers.
While the ice trays themselves don’t really contribute to sea level rise, since they’re already floating in the ocean, they act as dams to regulate the amount of ice released into the ocean from inside the Earth’s ice sheet. “We see that the ice shelves are becoming weaker and weaker,” explains Romain Millan, a glaciologist at Grenoble Alpes University and lead author of a new study. paper In Natural communications. “We observed that in response to this increased melting, glaciers are retreating and already releasing more ice into the ocean.”
Millan and his colleagues used satellites and models to check several aspects of the health of northern Greenland’s ice shelves. On the one hand, satellite imagery allowed them to determine how the total volume and total area of ice have decreased over the decades. Deeper, they were able to follow the “grounding line,” where the ice sheet rises from the land to become a floating ice floe. As the tides rise and fall, the ice rises and falls, a movement that is tracked by satellites to determine the exact location of grounding lines.
As ice shelves shrink and thin, these lines rapidly retreat inland, where topography adds even more problems. Moving inland from the coast, the slope of the bed is retrograde, meaning that the ground surface beneath the ice becomes deeper as one moves toward the center of the island . “If the anchor line begins to move backward, it could enter an unstoppable retreat because it is on a retrograde bed slope,” says Millan.
If, on the other hand, the slope went up as you travel inland it would be more difficult for the grounding line to move backward. Imagine how far inland floodwaters can travel if the terrain is flat rather than mountainous. “As the stranding moves to a deeper bed, the amount of ice from the bed to the surface is thicker, which means the amount of ice dumped into the ocean is greater,” says Millan. “As you go down, you also expose more ice to a warmer ocean, and therefore more melting, more acceleration, more releases.”