Photograph by Ralph Lee Hopkins, National Geographic

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Meltwater streams from ice near Svalbard, Norway.

Photograph by Ralph Lee Hopkins, National Geographic

Why Predicting Sea Ice Cover Is So Difficult

It's hard to pinpoint when the Arctic will be sea ice free in the summer.

Predicting Mother Nature is never an exact science. Weather forecasters can get it wrong, leaving people dressed for a rainy day high and dry. And the further out researchers try to predict things like air temperature or sea ice cover, the more uncertainty there is.

But knowing how Earth's climate will react to natural and human-induced changes is important for governments and industry. (Related: "As Arctic Ice Melts, Rush Is on for Shipping Lanes, More.")

Perhaps nowhere are the stakes as high as in the Arctic. The mineral, gas, and biological bounties are powerful economic attractions, drawing countries into a modern-age gold rush fueled by disappearing sea ice. (Related: "Russia Plants Underwater Flag, Claims Arctic Seafloor.")

Predicting when the Arctic will be sea ice free in the summer months has occupied researchers for years. Estimates under high greenhouse gas emissions range from the year 2011 to 2098.

The complexity of Earth's atmosphere and oceans, and our limited understanding of those processes, are the main drivers of that uncertainty, said Jiping Liu, a sea ice researcher at the University of Albany in New York.

Liu recently published a study that narrowed down the range, predicting an ice-free Arctic summer by 2054 to 2058, based on current climate models.

"We know the climate models are not perfect," he said. "[But] we have to rely on them to make predictions."


There are several unknowns in sea ice modeling, Liu explained. First, researchers don't know how the ice reacts to inputs of warm water from the Pacific and Atlantic Oceans. There is an increased flow of warmer water into the Arctic, but we don't know how much of it is transferred to sea ice, he said.

"The bottom of sea ice is very sensitive to temperature changes," even to changes as little as 0.1 to 0.2 degrees, Liu noted.

Current models may therefore be underestimating the decline of Arctic sea ice during the summers, Liu said. "[And in] this sense, maybe the Arctic will be ice-free earlier."

We also don't know how sunlight penetrates sea ice to reach the water below, he explained. Thicker ice prevents sunlight from reaching seawater, stopping it from warming. But thinner ice lets the light through. Current climate models do not describe this process accurately, said Liu.

Finally, it's hard to determine how much of the change in sea ice cover is due to natural variability and how much is due to external forcing such as global warming.

"From my stance, 50 to 70 percent of sea ice decline is probably due to the increase of greenhouse gases [in the atmosphere]," said Liu. But that's a large range of uncertainty that needs to be narrowed down further, he added.

Still Robust

Julienne Stroeve, a sea ice scientist at the National Snow and Ice Data Center, agrees that not all the models are perfect. But they still give us a good idea of how areas will change under various emissions scenarios, she said.

"They all say the Arctic will warm more than any other place," Stroeve added. But their estimates of ice loss are lower than what scientists have observed.

The models that Liu used in his study were global climate models, which operate at very coarse scales, she said. Finer details like the ocean circulation in the Beaufort Sea—which controls the motion of sea ice in the Beaufort region—aren't incorporated.

Neither are smaller scale processes such as the prevalence of openings in the sea ice, or the presence of melt ponds, Stroeve added. Both can accelerate the melting of sea ice. (Related: "Study Links Arctic Sea Ice Loss With Changes in Atmospheric Circulation.")

Weather also plays an important role in the presence of Arctic sea ice, "[and] we can't predict the weather," she said.

It could be quite possible to get an ice-free summer in the Arctic, Stroeve said. But if we swing into a period of colder weather, "these models do show that the ice can recover."

"I think these models are useful at looking at what's happening in the future," she said. "But they're not really useful for [figuring out] an exact date" for an ice-free summer in the Arctic.

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