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Ice sheet uncertainties could mean models underestimate sea level rise

New research suggests the predictions of current sea level rise models should be treated as conservative estimates. Photo by NASA / James Yungel / Flickr
New research suggests the predictions of current sea level rise models should be treated as conservative estimates. Photo by NASA / James Yungel / Flickr

Dec. 18 (UPI) -- If climate change continues unabated, sea level rise could exceed levels forecast by the Intergovernmental Panel on Climate Change, according to a new study.

The research, published Friday in the journal One Earth, suggests even the world's best sea level rise prediction models are riddled with uncertainty.

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Many of them, authors of the new paper contend, are likely underestimating the rate at which polar ice sheets are becoming destabilized.

Because the mechanics of polar ice loss are mostly hidden beneath thick layers of ice or a few hundred feet of ocean water, modeling the behavior of Greenland and Antarctica's ice sheets remains exceedingly difficult.

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"The polar regions are the most unexplored places on our planet," lead author Martin Siegert, glaciologist and professor at the Grantham Institute at Imperial College London, told UPI in an email.

"Satellite observations are an excellent way to find out what's happening, but they only measure effects at the surface of the ice/ocean," Siegert wrote.

"The processes controlling ice dynamics are all subsurface, and so while their effects on the surface can be measured, the processes themselves can't be resolved by satellites."

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For the new study, Siegert and his research partners surveyed the models used by the Intergovernmental Panel on Climate Change to make predictions about effects of global warming on polar ice loss and sea level rise.

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Their analysis revealed the models' biggest blind spots, most of which can be found where ocean currents meet the underbelly of ice shelves.

"Some uncertainties can be resolved with better subsurface measurement, such as the ocean cavity beneath ice shelves, but the key issues are how various components of the system will interact," Siegert said.

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"Specifically, how will ocean warmth flow under ice shelves, and melt the ice base and grounding line?"

To account for the many blind spots of the world's best ice sheet models, scientists must assign values -- rather than calculating values -- to a variety of important processes, including ice flow, fracturing, ice melting and ocean-heat transfer. Scientists call this imprecise approach "parameterization."

Despite the uncertainties that are baked into theses models, their predictions are being used to form important climate change policies. That's a problem, according to Siegert.

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"This parameterization is perfectly valid in the absence of observations -- what else can they do? -- but a health warning is needed so that the results can be interpreted fairly, recognizing that the parameterization may lead to an inability to model the real situation and interaction between processes," he said.

The designers of the world's best ice sheet simulations are aware of their models' shortcomings. In fact, efforts to understand the interplay between ice and ocean water along the grounding lines -- where the ocean floor meets the bottom of an ice sheet -- have greatly improve sea level rise precision models over the last few years.

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Researchers hope that robotic technologies will continue to provide new insights into the dynamics at play beneath ice shelves.

"Robotics will surely play a key role in accessing challenging to get to places in the ice-shelf-ocean-ice-sheet system," Siegert said. "This is the key location where ice sheet change is being driven, and without automated devices we will be left with sparse knowledge."

Despite the progress, the authors of the new paper argue that when it comes to crafting public policy related sea level rise, the predictions of current models should be treated as conservative estimates.

Previous studies of ice and sediment cores, as well as surveys of ancient marine fossils, suggest the planet's ice sheets rapidly destabilized during ancient periods of global warming, leading to more dramatic rates of sea level rise than are occurring today.

"We need to make decision makers more aware of the potential for [3-feet-plus] sea level rise this century," Siegert said.

"Through this awareness, plans for coastal and sea defense may need to be formed in such a way that they can be easily added to as and when sea level gets higher. This incremental adaptation would seem sensible, but we need to make the decisions to form such solutions now."

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