How do they do it? Predictions are in for Arctic sea ice low point

Aug 14, 2012

It's become a sport of sorts, predicting the low point of Arctic sea ice each year. Expert scientists with decades of experience do it but so do enthusiasts, whose guesses are gamely included in a monthly predictions roundup collected by Sea Ice Outlook, an effort supported by the U.S. government.

When averaged, the predictions have come in remarkably close to the mark in the past two years. But the low and high predictions are off by hundreds of thousands of square kilometers.

Researchers are working hard to improve their ability to more accurately predict how much Arctic will remain at the end of summer. It's an important exercise because knowing why sea ice declines could help scientists better understand and how sea ice is evolving.

This year, researchers from the University of Washington's Polar Science Center are the first to include new data collected by airplane in a prediction.

They expect 4.4 million square kilometers of remaining ice (about 1.7 million square miles), just barely more than the 4.3 million kilometers in 2007, the lowest year on record for . The median of 23 predictions collected by the Sea Ice Outlook and released on Aug. 13 is 4.3 million.

"One drawback to making predictions is historically we've had very little information about the thickness of the ice in the current year," said Ron Lindsay, a at the Polar Science Center, a department in the UW's Laboratory.

To make their prediction, Lindsay and Jinlun Zhang, an in the Polar Science Center, start with a widely used model pioneered by Zhang and known as the Pan-Arctic Ice Ocean Modeling and Assimilation System. That system combines available observations with a model to track sea ice volume, which includes both and extent.

But obtaining observations about current-year ice thickness in order to build their short-term prediction is tough. NASA is currently in the process of designing a new satellite that will replace one that used to deliver ice thickness data but has since failed. In the meantime, NASA is running a program called Operation IceBridge that uses airplanes to survey sea ice as well as sheets.

"This is the first year they made a concerted effort to get the data from the aircraft, process it and get it into hands of scientists in a timely manner," Lindsay said. "In the past, we've gotten data from submarines, moorings or satellites but none of that data was available in a timely manner. It took months or even years."

There's a shortcoming to the IceBridge data, however: It's only available through March. The radar used to measure snow depth on the surface of the ice, an important element in the observation system, has trouble accurately gauging the depth once it has melted and so the data is only collected through the early spring before the thaw.

The UW scientists have developed a method for informing their prediction that is starting to be used by others. Researchers have struggled with how best to forecast the weather in the Arctic, which affects ice melt and distribution.

"Jinlun came up with the idea of using the last seven summers. Because the climate is changing so fast, only the recent summers are probably relevant," Lindsay said.

The result is seven different possibilities of what might happen. "The average of those is our best guess," Lindsay said.

Despite the progress in making predictions, the researchers say their abilities to foretell the future will always be limited. Because they can't forecast the weather very far in advance and because the ice is strongly affected by winds, they have little confidence beyond what the long-term trend tells us in predictions that are made far in advance.

"The accuracy of our prediction really depends on time," Zhang said. "Our June 1 prediction for the Sept. 15 low point has high uncertainty but as we approach the end of June or July, the uncertainty goes down and the accuracy goes up."

In hindsight, that's true historically for the average predictions collected by Study of Environmental Arctic Change's Sea Ice Outlook, a project funded by the National Science Foundation and the National Oceanic and Atmospheric Administration.

While the competitive aspect of the predictions is fun, the researchers aren't in it to win it.

"Essentially it's not for prediction but for understanding," Zhang said. "We do it to improve our understanding of sea ice processes, in terms of how dynamic processes affect the seasonal evolution of sea ice."

That may not be entirely the same for the enthusiasts who contribute a prediction. One climate blog polls readers in the summer for their best estimate of the sea ice low point. It's included among the predictions collected by the Sea Ice Outlook, with an asterisk noting it as a "public outlook."

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User comments : 9

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Vendicar_Decarian
3.7 / 5 (6) Aug 14, 2012
Dug
1.4 / 5 (9) Aug 14, 2012
Soooo, isn't this also an admission that the data on sea ice thickness that was collected up to these newer more real time techniques was... unreliable an inadequate. And that was the basis for a large part of climate change's so-called scientific consensus up to this point? I guess science is a lot different than it used to be, because in the past data that wasn't reliable, or even questionable - it wasn't used. While I'm not a climate change denier, I am very much a skeptic of just how accurate the data is that we are using and how able and certain our predictions really are.
jerryd
4.4 / 5 (7) Aug 14, 2012
Dug, you can now run ships through the artic. That alone should tell you things have greatly changed.
rubberman
5 / 5 (3) Aug 15, 2012
Dug, you can now run ships through the artic. That alone should tell you things have greatly changed.


Add to this that any data collected today using modern data aquisition techniques is likely more reliable than the ones previously used. Of course standing on pretty much any shore of the artic ocean and seeing only water is pretty signifigant.
GSwift7
2.3 / 5 (3) Aug 15, 2012
Dug, you can now run ships through the artic. That alone should tell you things have greatly changed


Anctedotal evidence isn't really very meaningful. A person could counter your comment by simply pointing out that Vikings did the same 1000 years ago. Without understanding the complexities that determine cause and effect, it is unwise to draw too many conclusions unless you make it clear that your conclusions are based partly on assumptions and estimates.

Since the low point in 2007, it has been basically holding steady. Why has it done that? Hard to say right now. I think finding the answer will depend largely on what happens in the next 10-20 years. If it recovers, stays the same as it is, or resumes the previous decline, will tell us a lot about how it works. We know there is natural variability, but how much, and over what time scales? How much change, over what time period really indicates large scale permanent change? We will see eventually.
GSwift7
2.3 / 5 (3) Aug 15, 2012
Add to this that any data collected today using modern data aquisition techniques is likely more reliable than the ones previously used


Good point but there remains a few difficulties which confound even today's best techniques. For example, when you get a pond of melt water standing on top of solid ice, some of the hi-tech instruments cannot distinguish that from open water. Cloud cover, especially low fog, is still difficult to distinguish from ice in satellite pictures. With photo resolution of 1 meter per pixel, it is difficult to get the exact proportion of ice to water in areas filled with loose pack ice. Wind still moves the ice around more than most people realize on a daily basis, which means that you might photograph the same piece of ice twice in different passes of a satellite over different areas, or miss some ice by the opposite effect. The above only deals with ice area, but thickness is an issue too.
Vendicar_Decarian
5 / 5 (3) Aug 15, 2012
The answer to your question is simple. Sea ice hasn't held steady since 2007, and your presumption is faulty.

"Since the low point in 2007, it has been basically holding steady. Why has it done that?" - GnotsoSwift

Sea ice area does not equate to sea ice volume. As to sea ice area, we are 3 weeks from the start of the re-freeze and the area is near record lows. Here are some projections... https://sites.goo...e/piomas
Vendicar_Decarian
5 / 5 (3) Aug 15, 2012
Currently Arctic ice extent corresponds to 3.097 million square kilometers, and will soon be 2.7 million square kilometers.

If you can find something on the order of a half million square kilometers of standing water on the broken ice that remains, please feel free to write a paper on you discovery.

Otherwise, your complaint has no significant impact.

"For example, when you get a pond of melt water standing on top of solid ice, some of the hi-tech instruments cannot distinguish that from open water." - Gswift
Vendicar_Decarian
4 / 5 (4) Aug 15, 2012
Only if you are willing to conjure non-existent facts to foster the claim that the vikings paddled their boats through the arctic.

"A person could counter your comment by simply pointing out that Vikings did the same 1000 years ago." - GSwift

Manufacturing facts is frowned upon in science.

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