Earth may face a huge issue in the coming decades: sea level rise. Exactly how high ocean waters will become, though, has been cause for speculation among scientists. Now, researchers have discovered that stretches of ice on the coasts of Antarctica and Greenland are at risk of rapidly cracking apart and falling into the ocean. This could mean that sea level rise will be on the upper end of current model projections.

Iceberg calving is the formation of icebergs. These marine chunks of ice are born when massive pieces break off of larger shelves, or glaciers, and then float away. Eventually, these icebergs melt in warmer oceans and add to the amount of water available. Despite the fact that iceberg calving accounts for roughly half of the mass lost from ice sheets, though, it isn't reflected in any models of how climate change affects the ice sheets.

"Fifty percent of the total mass loss from the ice sheets we just don't understand," said Jeremy Bassis of the U-M College of Engineering in a news release. "We essentially haven't been able to predict that, so events such as rapid disintegration aren't included in those estimates. Our new model helps us understand the different parameters, and that gives us hope that we can better predict how things will change in the future."

In order to understand how iceberg calving might affect sea levels, the researchers delved into the physics of icebergs. They created a model that can simulate the different processes that occur on both ends of the Earth. For example, it takes into account that in northern latitudes, where icebergs rest on solid ground, icebergs tend to form in relatively small, vertical slivers that can rotate onto their sides as they dislodge. It also takes into account that in southern latitudes, icebergs form in larger, more horizontal plank shapes.

"Essentially, everything is driven by gravity," said Bassis. "We identified a critical threshold of one kilometer where it seems like everything should break up. You can think of it in terms of a kid building a tower. The taller the tower is, the more unstable it gets."

In the end, the researchers found that runaway iceberg calving can occur. As ice thins and cracks form, ice sheets and glaciers become more susceptible to collapse and breakup. This means that icebergs could significantly contribute to sea level rise and should certainly be included in current models.

The findings were published in the journal Nature Geoscience.