In the Southern Hemisphere, the ice cover around Antarctica gradually expands from March to October each year. During this time the total ice area increases by 6 times to become larger than Russia. The sea ice then retreats at a faster pace, most dramatically around December, when Antarctica experiences constant daylight.

New research led by the 天美影视传媒 explains why the ice retreats so quickly: Unlike other aspects of its behavior, Antarctic sea ice is just following simple rules of physics.

The was published March 28 in Nature Geoscience.

鈥淚n spite of the puzzling longer-term trends and the large year-to-year variations in Antarctic sea ice, the seasonal cycle is really consistent, always showing this fast retreat relative to slow growth,鈥� said lead author , who conducted the study as a postdoctoral researcher at the UW and is now a research scientist at NASA and Columbia University. 鈥淕iven how complex our climate system is, I was surprised that the rapid seasonal retreat of Antarctic sea ice could be explained with such a simple mechanism.鈥�

Previous studies explored whether or warm ocean waters might be responsible for the asymmetry in Antarctica鈥檚 seasonal sea ice cycle. But the new study shows that, just like a hot summer day reaches its maximum sizzling conditions in late afternoon, an Antarctic summer hits peak melting power in midsummer, accelerating warming and sea ice loss, with slower changes in temperature and sea ice when solar input is low during the rest of the year.

The researchers investigated global climate models and found they reproduced the quicker retreat of Antarctic sea ice. They then built a simple physics-based model to show that the reason is the seasonal pattern of incoming solar radiation.

Near the North Pole, Arctic ice cover has gradually decreased since the 1970s with global warming. Antarctic ice cover, however, has seesawed over recent decades. Researchers are still working to understand sea ice around the South Pole and better represent it in climate models.

鈥淚 think because we usually expect Antarctic sea ice to be puzzling, previous studies assumed that the rapid seasonal retreat of Antarctic sea ice was also unexpected 鈥� in contrast to the Arctic, where the seasons of ice advance and retreat are more similar,鈥� Roach said. 鈥淥ur results show that the seasonal cycle in Antarctic sea ice can be explained using very simple physics. In terms of the seasonal cycle, Antarctic sea ice is behaving as we should expect, and it is the Arctic seasonal cycle that is more mysterious.鈥�

The researchers are now exploring why Arctic sea ice doesn鈥檛 follow this pattern, instead each year growing slightly faster over the Arctic Ocean than it retreats. Because Antarctica鈥檚 geography is simple, with a polar continent surrounded by ocean, this aspect of its sea ice may be more straightforward, Roach said.

鈥淲e know the Southern Ocean plays an important role in Earth鈥檚 climate. Being able to explain this key feature of Antarctic sea ice that standard textbooks have had wrong, and showing that the models are reproducing it correctly, is a step toward understanding this system and predicting future changes,鈥� said co-author , a UW professor of atmospheric sciences.

Other co-authors are , a UW research assistant professor in atmospheric sciences; Ian Eisenman at Scripps Institution of Oceanography; and Till Wagner at the University of Wisconsin-Madison. Roach is currently a research scientist with the NASA Goddard Institute for Space Studies. This work was funded by the National Science Foundation, the National Oceanic and Atmospheric Administration and the U.K.-based Scientific Committee on Antarctic Research.

For more information, contact Roach at l.roach@columbia.edu.

In the past 20 years, the Arctic has lost about one-third of its winter sea ice volume, according to a new study by researchers at the 天美影视传媒 and the California Institute of Technology. That decline is largely due to loss of older, multiyear sea ice. New satellite data also show that wintertime Arctic sea ice is likely thinner than previous estimates.

The was published March 10 in Geophysical Research Letters.

鈥淭he key takeaway, for me, is the remarkable loss of Arctic winter sea ice volume 鈥� one-third of the winter ice volume lost over just 18 years 鈥� that accompanied a widely reported loss of old, thick Arctic sea ice, and decline in end-of-summer ice extent,鈥� said co-author , a polar scientist at the UW Applied Physics Laboratory.

Seasonal sea ice, which melts completely each summer rather than accumulating over years, is replacing thicker, multiyear ice. This switch is largely responsible for the sea ice thinning, according to the new research.

鈥淎rctic snow depth, sea ice thickness and volume are three very challenging measurements to obtain,鈥� Kwok remarked.

The newest technology, a combination of ICESat-2 lidar data and CryoSat-2 radar data, is able for the first time to estimate the depth of the snow on top of the Arctic sea ice. Using snow depth and the height of sea ice exposed above water, the study found that multiyear Arctic sea ice lost 16% of its winter volume, or approximately half a meter (about 1.5 feet) of thickness, in the three years since the launch of ICESat-2 in 2018.

鈥淲e weren鈥檛 really expecting to see this decline, for the ice to be this much thinner in just three short years,鈥� said lead author at CalTech鈥檚 Jet Propulsion Laboratory.

Scientists estimate sea ice thickness using snow depth and the height of the floating ice above the sea surface. Snow can weigh ice down, changing how ice floats in the ocean. The new study compared ice thickness using snow depths from satellite radar and lidar to previous observations of ice thickness and snow depth from climate records. The comparisons show that using climatology-based estimates of snow depth can result in overestimating sea ice thickness by up to one-fifth, or as much as 20 centimeters (0.7 feet).

To provide context for sea ice thickness estimates from 2018 to 2021, the study used an 18-year record of sea ice observations spanning the older ICESat records and the newer ICESat-2 and CryoSat-2 satellites to capture monthly changes in Arctic sea ice thickness and volume. The longer 18-year record showed a loss of about 6,000 cubic kilometers (1,400 cubic miles) of winter ice volume, or about one-third, largely driven by the switch from predominantly multiyear ice to thinner, seasonal sea ice.

Older, multiyear ice tends to be thicker and therefore more resistant to melting. As that 鈥渞eservoir鈥� of old Arctic sea ice declines and seasonal ice becomes the norm, the overall thickness and volume of Arctic sea ice is expected to drop further.

鈥淐urrent models predict that by the mid-century we can expect ice-free summers in the Arctic, when the older ice, thick enough to survive the melt season is gone,鈥� Kacimi said.

For more information, contact Kwok at rkwok@apl.washington.edu or Kacimi at sahra.kacimi@jpl.nasa.gov

This article was adapted from a by the American Geophysical Union.

In February 2018, a vast expanse of open water appeared in the sea ice above Greenland, a region that normally has sea ice well into the spring. The big pool of open water in the middle of the ice, known as a , was .

New analysis by researchers at the 天美影视传媒 and the University of Toronto Mississauga shows that odd winds are to blame, not simple global warming. The was published Dec. 6 in Geophysical Research Letters.

Although last winter did see unusually warm in the Arctic, the authors identify the cause to be strong surface winds triggered by a dramatic warming in Earth’s upper atmosphere, known as a “.”

“During these events, temperatures in the stratosphere 鈥� about 30 kilometers above ground level 鈥� can warm by 10 or 15 degrees Celsius in just a few days,” said lead author , at the University of Toronto Mississauga.

The sudden warming of 18 to 27 F at some 18 miles elevation shifts air pressure and thus circulation patterns. In February 2018, it caused winds from Siberia to blow cold air into Northern Europe, creating a weather system that became known as the “.” That same weather pattern drew warmer air north up the east coast of Greenland, and generated persistent strong winds.

“This [wind pattern] lasted a week, and these were the warmest temperatures and strongest winds observed in north Greenland since observations began in the 1960s,” Moore said. “Winds were close to hurricane force and temperatures were above freezing. Once we got that piece of the puzzle, we realized it could be wind rather than warmth that caused the polynya.”

The study relied on a UW tool, the , or PIOMAS, to reconstruct sea ice conditions in the Arctic Ocean.

The authors used PIOMAS to run a simulation with the atmospheric conditions of 2018 but with thicker sea ice that was present in the Arctic in 1979, to see if thinner sea ice due to climate change caused the open water to appear. The patch of open water in that area was unprecedented in observations and lasted about three weeks, from mid-February through the first week of March.

“We used to ask the question hypothetically: What would have happened if the ice had been as thick as in 1979?” said co-author , a polar scientist at the UW’s Applied Physics Laboratory. “Now, we simulate it. The answer was that the thinning of the ice didn鈥檛 matter much, but strong winds were responsible.”

A longtime sea ice researcher, Schweiger was surprised. He thought thinning ice would be the decisive factor.

“But when we looked closer, it wasn鈥檛. Letting your intuition guide your hypothesis, then letting yourself be convinced otherwise 鈥� that’s science,” he said.

The other co-authors on the study are and , both in the UW Applied Physics Laboratory.

The UW tool is also commonly used to gauge the total volume of Arctic sea ice in a given month. Overall the UW tool shows the minimum volume of Arctic sea ice, reached in September, has recovered slightly from its all-time low in 2012, but is still following a long-term decline over the past four decades.

“We鈥檝e lost about half of the extent, we鈥檝e lost half of the thickness, and if you multiply these two things, we鈥檝e lost 75 percent of the September sea ice,” Schweiger recently .

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For more information, contact Schweiger at schweig@uw.edu or 206-543-1312 and Moore at gwk.moore@utoronto.ca or 905-569-5766. (Note: Schweiger is traveling Dec. 17-27 with limited email access.)

Adapted from a University of Toronto .

A dramatic drop in Antarctic sea ice almost a year ago, during the Southern Hemisphere spring, brought its maximum area down to its lowest level in 40 years of record keeping. Ocean temperatures were also unusually warm. This exceptional, sudden nosedive in Antarctica differs from the long-term decline in the Northern Hemisphere. A new 天美影视传媒 study shows that the lack of Antarctic sea ice in 2016 was in part due to a unique one-two punch from atmospheric conditions both in the tropical Pacific Ocean and around the South Pole.

The was published Aug. 24 in Geophysical Research Letters.

“This combination of factors, all these things coming together in a single year, was basically the ‘perfect storm,’ for Antarctic sea ice,” said corresponding author , a UW postdoctoral researcher in atmospheric sciences. “While we expect a slow decline in the future from global warming, we don’t expect such a rapid decline in a single year to happen very often.”

The area of sea ice around Antarctica at its peak in late 2016 was 2 million square kilometers (about 800,000 square miles) less than the average from the satellite record. Statistically, this is three standard deviations away from the average 鈥� an event that would be expected to occur randomly just once every 300 years.

The record low was not predicted by climate scientists, so UW researchers looked at the bigger picture in ocean and atmospheric data to explain why it happened.

The previous year, 2015-16, had a very strong El Ni帽o in the tropical Pacific Ocean. Nicknamed the “,” the event was similar to other monster El Ni帽os in 1982-83 and 1997-98. Unlike the 1997-98 event, however, it was only followed by a relatively weak La Ni帽a in 2016.

Far away from the tropics, the tropical El Ni帽o pattern creates a series of high- and low-pressure zones that cause unusually warm ocean temperatures in Antarctica’s eastern Ross, Amundsen and Bellingshausen seas. But in 2016, when no strong La Ni帽a materialized, researchers found that these unusually warm surface pools lingered longer than usual and affected freeze-up of seawater the following season.

“I’ve spent many years working on tropical climate and El Ni帽o, and it amazes me to see its far-reaching impacts,” Stuecker said.

Meanwhile, observations show that the winds circling Antarctica were unusually weak in 2016, meaning they did not push sea ice away from the Antarctic coast to make room for the formation of new ice. This affected ice formation around much of the Southern Ocean.

“This was a really rare combination of events, something that we have never seen before in the observations,” Stuecker said.

The researchers analyzed 13,000 years of climate model simulations to study how these unique conditions would affect the sea ice. Taken together, the El Ni帽o pattern and Southern Ocean winds explain about two-thirds of the 2016 decline. The rest may be due to , which a previous paper suggested had broken up ice floes.

Scientists predict Antarctica’s ocean will be one of the to experience global warming. Eventually the Southern Ocean’s surface will begin to warm, however, and then sea ice there will begin its more long-term decline.

“Our best estimate of the Antarctic sea ice turnaround point is sometime in the next decade, but with high uncertainty because the climate signal is small compared to the large variations that can occur from one year to the next,” said co-author , a UW professor of atmospheric sciences.

Stuecker noted that this type of big, rare weather event is useful to help understand the physics behind sea ice formation, and to learn how best to explain the observations.

“For understanding the climate system we must combine the atmosphere, ocean and ice, but we must focus on more than a specific region,” Stuecker said. “If we want to understand sea ice in Antarctica, we cannot just zoom in locally 鈥� we really have to take a global perspective.”

The other co-author is , a UW assistant professor of atmospheric sciences and oceanography. The research was funded by the National Science Foundation and a National Oceanographic and Atmospheric Administration’s Climate and Global Change Postdoctoral Fellowship Program, administered by the University Corporation for Atmospheric Research’s for the Advancement of Earth System Science.

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For more information, contact Stuecker at stuecker@atmos.washington.edu or Bitz at bitz@uw.edu and reach either scientist at 206-543-1339.

A finds that a substantial chunk of summer sea ice loss in recent decades was due to natural variability in the atmosphere over the Arctic Ocean. The study, from the 天美影视传媒, the University of California Santa Barbara and federal scientists, is published March 13 in Nature Climate Change.

“Anthropogenic forcing is still dominant 鈥� it’s still the key player,” said first author , a climate scientist at the University of California Santa Barbara who holds an affiliate position at the UW, where he began the work as a research scientist in the UW’s Applied Physics Laboratory. “But we found that natural variability has helped to accelerate this melting, especially over the past 20 years.”

The paper builds on previous work by Ding and other UW scientists that found changes in the tropical Pacific Ocean have in recent decades that has boosted warming in that region.

The hot spot is a large region of higher pressure where air is squeezed together so it becomes warmer and can hold more moisture, both of which bring more heat to the sea ice below. The new paper focuses specifically on what this atmospheric circulation means for Arctic sea ice in September, when the ocean reaches its maximum area of open water.

“The idea that natural or internal variability has contributed substantially to the Arctic sea ice loss is not entirely new,” said second author , a 天美影视传媒 polar scientist who tracks Arctic sea ice. “This study provides the mechanism, and uses a new approach to illuminate the processes that are responsible for these changes.”

Ding designed a new sea ice model experiment that combines forcing due to climate change with observed weather in recent decades. The model shows that a shift in wind patterns is responsible for about 60 percent of sea ice loss in the Arctic Ocean since 1979. Some of this shift is related to climate change, but the study finds that 30-50 percent of the observed sea ice loss since 1979 is due to natural variations in this large-scale atmospheric pattern.

“What we’ve found is that a good fraction of the decrease in September sea ice melt in the past several decades is most likely natural variability. That鈥檚 not really a surprise,” said co-author , a UW professor of atmospheric sciences.

“The method is really innovative, and it nails down how much of the observed sea ice trend we’ve seen in recent decades in the Arctic is due to natural variability and how much is due to greenhouse gases.”

The long-term natural variability is ultimately thought to be driven by the tropical Pacific Ocean. Conditions in the tropical Pacific set off ripple effects, and atmospheric waves snake around the globe to create areas of higher and lower air pressure.

Teasing apart the natural and human-caused parts of sea ice decline will help to predict future sea ice conditions in Arctic summer. Forecasting sea ice conditions is relevant for shipping, climate science, Arctic biology and even tourism. It also helps to understand why sea ice declines may be faster in some decades than others.

“In the long term, say 50 to 100 years, the natural internal variability will be overwhelmed by increasing greenhouse gases,” Ding said. “But to predict what will happen in the next few decades, we need to understand both parts.”

What will happen next is unknown. The tropical Pacific Ocean could stay in its current phase or it could enter an opposite phase, causing a low-pressure center to develop over Arctic seas that would temporarily slow the long-term loss of sea ice due to increased greenhouse gases.

“We are a long way from having skill in predicting natural variability on decadal time scales,” Ding said.

The research was funded by NOAA, the National Science Foundation, NASA and the Tamaki Foundation. Other co-authors are Stephen Po-Chedley, Edward Blanchard-Wrigglesworth and Ryan Eastman in the UW’s Department of Atmospheric Sciences; Eric Steig in the UW’s Department of Earth and Space Sciences; and Michelle L’Heureux, Kristin Harnos and Qin Zhang at the National Oceanographic and Atmospheric Administration’s Climate Prediction Center.

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For more information, contact Ding at qinghua@ucsb.edu, Schweiger at 206-543-1312 or聽axel@apl.uw.edu and Battisti at 206-543-2019 or battisti@uw.edu.

NOAA: NA15OAR4310162; NSF: ARC-1203425; NASA: NNXBAQ35G

, a polar scientist at the 天美影视传媒’s Applied Physics Laboratory, has been studying the Arctic Ocean for decades, and sailed part of the Northwest Passage in 2009. Stern’s latest work uses the earliest explorers’ experiences to better understand a maritime environment that still contains many unknowns. A published in November in Polar Geography uses Captain James Cook’s records of sea-ice edge, more than two centuries ago, as a way to understand the changes we’re seeing now. UW Today asked him a few questions about the project.

How did you come to publish a paper about this historical map of Arctic sea ice?

It started when I was writing a book chapter called “” for a book by 天美影视传媒 Press. In the course of researching Cook’s 1778 foray into the Arctic, I realized that he had sailed close to the ice edge, and that his officers had made detailed charts of their positions. It didn’t take long to figure out that these were the earliest historical records of the ice edge in the Chukchi Sea.

Where did you find the map?

The definitive versions of Captain Cook’s journals were published in several volumes in the 1950s and 1960s. Accompanying them is a large-format collection, “Charts & Views Drawn by Cook and his Officers and Reproduced from the Original Manuscripts.” Both are available at Suzzallo Library. In looking through the large-format collection, I found the chart by naval officer that became Figure 1 of my paper. The figure is actually just a portion of his original chart.

To learn more about it, I went to UW Libraries Special Collections and found “The Charts and Coastal Views of Captain Cook鈥檚 Voyages,” which had a lot of useful information, including reproductions of other charts made by Cook and his officers. There I also found a first edition, from 1784, of the published account of Cook’s third voyage. The original charts from that voyage are in various places around the world, including the U.K. and Australia, so I have not yet seen an original chart.

You note that the ice has been quickly retreating since the 1990s. Why have we only begun to see this in recent decades?

For hundreds of years 鈥� or maybe longer 鈥� the ice edge in the Chukchi Sea in August varied from year to year, but on average it was more or less where Cook found it in August 1778. With global warming, things began to change, but the cumulative effect before the 1990s was not noticeable above the year-to-year variability inherent in the system. Sometime in the 1990s the “signal” began to emerge from the background “noise” 鈥� that is, the northward retreat of the ice edge became larger than the typical year-to-year variability of the August ice edge. That’s when we started to notice that things were changing.

What strikes you most about the changes to Arctic sea ice since Cook’s failed voyage?

In the last 10 to15 years, the changes have been dramatic. The summer ice edge in the Chukchi Sea is now hundreds of miles farther north than it used to be. This has opened up the opportunity for many ships, mostly private yachts, to transit the Northwest Passage, and for oil companies to consider drilling in the Chukchi Sea. It’s also like polar bears and beluga whales. But one thing hasn’t changed: it’s still dangerous to navigate through ice-covered waters.

When will the Arctic Ocean be ice-free in summer, and when might the Northwest Passage be used for navigation?

Climate models predict a nearly ice-free summer Arctic Ocean by about 2060, but with a large spread among models (some predict decades earlier, some decades later). However, the actual observational record over the last 35 years shows that most models are too conservative and that a nearly ice-free summer Arctic Ocean is more likely to arrive in the 2020 to 2040 timeframe. Note that “nearly ice-free” is commonly used to mean that the ice extent in the Arctic Ocean is 1 million square kilometers or less. This compares with 7 to 8 million square kilometers for the summer sea-ice extent before the year 2000, and about 5 million sq. km in more recent years.

The Northwest Passage is a long and complex series of channels and waterways that wind through the Canadian Arctic Archipelago. While the Northwest Passage has been open in recent summers to small boats and occasional , it is not yet a commercially viable shipping route, for several reasons: ice can still be a hazard, the route is shallow and narrow in places, there are very few aids to navigation and there is no search-and-rescue capability in place.

I wouldn’t expect the Northwest Passage to become a major commercial shipping route anytime soon. On the other hand, the Northern Sea Route, which passes along the north coast of Russia, has been handling an increasing amount of commercial traffic in recent years and is probably a more viable shipping route. The Northwest Passage will continue to see more “destinational” shipping (e.g., to a northern port and then out by the same route) and more small-boat traffic.

Does anything else strike you about this map?

The chart included as Figure 1 in my paper is interesting beyond the fact that one can deduce the approximate sea-ice edge from it. It contains a handwritten note by calling attention to a “gross mistake” in which the same island has been plotted as two separate islands. Bligh writes: “How they have blundered to lay them down as two I cannot conceive.” Bligh was an officer on Cook’s third voyage, 1776-1780, but he is better known in connection with the mutiny on the HMS Bounty in 1789.

The chart also contains the handwritten word “Lisburne” at the site of Alaska’s modern-day Cape Lisburne, but it is not known who wrote that word on the chart, nor who came up with the name. Details like that add interest to the chart.

My dad is an antique map dealer, so maybe that’s where my interest comes from.

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For more information, contact Stern at 206-543-7253 or hstern@uw.edu.

So far, this summer’s melt season is following the overall downward trend in sea ice area, as seen from NASA satellites. A 天美影视传媒 tool tallies a related value 鈥� the volume of floating Arctic ice. As of this week, it found the total mass of ice in the Arctic Ocean is at its second-lowest recorded volume for the beginning of July.

“The ice seems to be pretty thin,” said , a polar scientist with the UW’s Applied Physics Laboratory. “It’s essentially tied with 2011 and 2012, which were also pretty low at this time of year.”

Schweiger is one of the developers of the Pan-Arctic Ice Ocean Modeling and Assimilation System, or , which combines weather observations, sea-surface temperature and satellite pictures of ice coverage to compute ice volume and then compares that with on-the-ground measurements. The tool is widely used to assess the volume of ice in the Arctic Ocean, now an area closely looked at for fishing, navigation, oil exploration and even .

PIOMAS ice numbers starred in an animated graphic posted this week by a climate scientist at the University of Reading:

Meanwhile, in the Arctic, sea ice volume is at a record low for the time of year according to PIOMAS.

— Ed Hawkins (@ed_hawkins)

“I previously made a similar spiral for global temperatures which proved popular,” creator wrote in an email. “Sea ice was an obvious variable to look at next as it has a trend in the opposite direction.”

His graphic captures the overall downward trend in ice volume, as well as the seasonal cycle and the differences from one year to the next.

“It’s an interesting way of visualizing it,” Schweiger said. “By these circles getting smaller, you see overall that the ice volume is shrinking, but you also see the seasonal differences with September values decreasing more than the winter values.”

PIOMAS data had previously starred in the “” showing colored lines that each represent a month of ice volume spiraling in toward the center. It has also appeared as , animated , a featured in Wired magazine, and a of more standard graphs of Arctic sea ice.

Human-generated emissions are slowly boosting carbon dioxide levels to cause gradual temperature increases, which in turn create the closely-watched retreat of Arctic sea ice.

The March was the smallest in the satellite record, and the over the month of June was also a record low. The areal extent of Arctic sea ice, as by the U.S. National Snow and Ice Data Center in Colorado, is dancing around its 2012 record low.

“Whatever ice was gained in 2015, that seems to have been lost, and we’re continuing on a long-term downward trend,” Schweiger said.

The newly released June ice volume numbers from PIOMAS show an average volume of 16,500 cubic kilometers, which is about identical to 2011 and just above the 2012 all-time low.

“The June volume is just a little bit shy of the record, but the difference is within the noise in terms of the accuracy of the data,” Schweiger said. “Right now, based on volume, it’s technically a tie with 2012,” he said. “What that means for September is unclear.”

The fate of the ice this summer will depend on the weather over coming months, especially temperature, cloud cover, wind and storms.

Arctic sea ice reached an all-time low in September 2012. UW research since that although a huge August storm helped break up more ice floes, that record was mainly due to warm temperatures.

In a recent compilation of expert for this year, Schweiger and UW colleague estimated that Arctic sea ice will close out this fall at about 4.2 million square kilometers 鈥� more than the 3.63 million square kilometers low in 2012, but below the previous second-lowest level of 4.32 million square kilometers in 2007. If their prediction holds up, this summer will be among the three largest amounts of open water seen to date in the Arctic Ocean.

“I don’t think we know one way or the other,” Schweiger said. “It will essentially depend on the weather between now and the fall.”

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For more information, contact Schweiger at axel@apl.washington.edu or 206-543-1312. Download the sea ice volume animation .

The , published in The Cryosphere, show a thinning in the central Arctic Ocean of 65 percent between 1975 and 2012. September ice thickness, when the ice cover is at a minimum, is 85 percent thinner for the same 37-year stretch.

“The ice is thinning dramatically,” said lead author , a climatologist at the UW . “We knew the ice was thinning, but we now have additional confirmation on how fast, and we can see that it’s not slowing down.”

The study helps gauge how much the climate has changed in recent decades, and helps better predict an Arctic Ocean that may soon be ice-free for parts of the year.

The project is the first to combine all the available observations of Arctic sea ice thickness. The earlier period from 1975 to 1990 relies mostly on under-ice submarines. Those records are less common since 2000, but have been replaced by a host of airborne and satellite measurements, as well as other methods for gathering data directly on or under the ice.

“A number of researchers were lamenting the fact that there were many thickness observations of sea ice, but they were scattered in different databases and were in many different formats,” Lindsay said. The U.S. National Oceanic and Atmospheric Administration funded the effort to compile the various records and match them up for comparison.

The data also includes the NASA that operated from 2003 to 2008, that NASA is conducting until its next satellite launches, long-term under-ice from the Woods Hole Oceanographic Institution, and other measures from aircraft and instruments anchored to the seafloor.

The older submarine records were unearthed for science by former UW professor Drew Rothrock, who of ice thickness to first establish the thinning of the ice pack through the 1990s. Vessels carried upward-looking sonar to measure the ice draft so they knew where they could safely surface. of those records found a 36 percent reduction in the average thickness in the quarter century between 1975 and 2000.

“This confirms and extends that study,” Lindsay said. The broader dataset and longer time frame show that what had looked like a leveling off in the late 1990s was only temporary. Instead, adding another 12 years of data almost doubles the amount of ice loss.

The observations included in the paper all have been entered in the that now includes around 50,000 monthly measurements standardized for location and time. The archive is curated by scientists at the UW Applied Physics Laboratory and stored at the .

Lindsay also is part of a UW group that produces a widely cited that combines weather data, sea-surface temperatures and satellite measurements of sea ice concentration to generate ice thickness maps. Critics have said those estimates of sea ice losses seemed too rapid and questioned their base in a numerical model. But the reality may be changing even faster than the calculations suggest.

“At least for the central Arctic basin, even our most drastic thinning estimate was slower than measured by these observations,” said co-author , a polar scientist at the UW Applied Physics Laboratory.

The new study, he said, also helps confirm the methods that use physical processes to calculate the volume of ice each month.

“Using all these different observations that have been collected over time, it pretty much verifies the trend that we have from the model for the past 13 years, though our estimate of thinning compared to previous decades may have been a little slow,” Schweiger said.

The new paper only looks at observations up to the year 2012, when the summer sea ice level reached a record low. The two years since then have had slightly more sea ice in the Arctic Ocean, but the authors say they are not surprised.

“What we see now is a little above the trend, but it’s not inconsistent with it in any way,” Lindsay said. “It’s well within the natural variability around the long-term trend.”

Additional funding for the project was from the National Science Foundation and NASA.

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For more information, contact Lindsay at rlindsay@uw.edu or Schweiger at 206-543-1312 or schweig@uw.edu.

From research stations drifting on ice floes to high-tech aircraft radar, scientists have been tracking the depth of snow that accumulates on Arctic sea ice for almost a century. Now that people are more concerned than ever about what is happening at the poles, research led by the 天美影视传媒 and NASA confirms that snow has thinned significantly in the Arctic, particularly on sea ice in western waters near Alaska.

A , now online in the Journal of Geophysical Research: Oceans, combines data collected by ice buoys and NASA aircraft with historic data from ice floes staffed by Soviet scientists from the late 1950s through the early 1990s to track changes over decades.

Historically, Soviets on drifting sea ice used meter sticks and handwritten logs to record snow depth. Today, researchers on the ground use an automated probe similar to a ski pole to verify the accuracy of airborne measurements.

“When you stab it into the ground, the basket move up, and it records the distance between the magnet and the end of the probe,” said first author , a UW graduate student in oceanography. “You can take a lot of measurements very quickly. It’s a pretty big difference from the Soviet field stations.”

Webster verified the accuracy of airborne data taken during a March 15, 2012 NASA flight over the sea ice near Barrow, Alaska. The following day Webster followed the same track in minus 30-degree temperatures while stabbing through the snow every two to three steps.

The authors compared data from NASA airborne surveys, collected between 2009 and 2013, with U.S. Army Corps of Engineers buoys frozen into the sea ice, and earlier data from Soviet drifting ice stations in 1937 and from 1954 through 1991. Results showed that snowpack has thinned from 14 inches to 9 inches (35 cm to 22 cm) in the western Arctic, and from 13 inches to 6 inches (33 cm to 14.5 cm) in the Beaufort and Chukchi seas, west and north of Alaska.

That’s a decline in the western Arctic of about a third, and snowpack in the Beaufort and Chukchi seas less than half as thick in spring in recent years compared to the average Soviet-era records for that time of year.

“Knowing exactly the error between the airborne and the ground measurements, we’re able to say with confidence, Yes, the snow is decreasing in the Beaufort and Chukchi seas,” said co-author , an oceanographer at the UW’s Applied Physics Laboratory.

The authors speculate the reason for the thinner snow, especially in the Beaufort and Chukchi seas, may be that the surface freeze-up is happening later in the fall so the year’s heaviest snowfalls, in September and October, mostly fall into the open ocean.

What thinner snow will mean for the ice is not certain. Deeper snow actually shields ice from cold air, so a thinner blanket may allow the ice to grow thicker during the winter. On the other hand, thinner snow cover may allow the ice to melt earlier in the springtime.

Thinner snow has other effects, Webster said, for animals that use the snow to make dens, and for low-light microscopic plants that grow underneath the sea ice and form the base of the Arctic food web.

The new results support a 15-year-old UW-led study in which Russian and American scientists first analyzed the historic Arctic Ocean snow measurements. That detected a slight decline in spring snow depth that the authors believed, even then, was due to a shorter ice-covered season.

“This confirms and extends the results of that earlier work, showing that we continue to see thinning snow on the Arctic sea ice,” said Rigor, who was also a co-author on the earlier paper.

The recent fieldwork was part of NASA’s Operation program, which is using aircraft to track changes while NASA prepares to launch a new ice-monitoring satellite in 2017. The team conducted in spring 2012 as part of a larger program to monitor changes in the Arctic.

The research was supported by NASA and the U.S. Interagency Arctic Buoy Program. Co-authors are Son Nghiem at NASA’s Jet Propulsion Laboratory, Nathan Kurtz at NASA’s Goddard Space Flight Center, Sinead Farrell at the University of Maryland, Don Perovich at the federal Cold Regions Research and Engineering Laboratory and Matthew Sturm at the University of Alaska Fairbanks.

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For more information, contact Webster at melindaw@uw.edu and Rigor at 206-685-2571 or ignatius@apl.washington.edu.

More images are available at聽 www.flickr.com/uwnews.

A 天美影视传媒 researcher made the first study of waves in the middle of the Arctic Ocean, and detected house-sized waves during a September 2012 storm. The results were recently published in .

“As the Arctic is melting, it’s a pretty simple prediction that the additional open water should make waves,” said lead author , an oceanographer with the UW .

His data show that winds in mid-September 2012 created waves of 5 meters (16 feet) high during the peak of the storm. The research also traces the sources of those big waves: high winds, which have always howled through the Arctic, combined with the new reality of open water in summer.

Arctic ice used to retreat less than 100 miles from the shore. In 2012, it retreated more than 1,000 miles. Wind blowing across an expanse of water for a long time creates whitecaps, then small waves, which then slowly consolidate into big swells that carry huge amounts of energy in a single punch.

The size of the waves increases with the fetch, or travel distance over open water. So more open water means bigger waves. As waves grow bigger they also catch more wind, driving them faster and with more energy.

Shipping and oil companies have been eyeing the opportunity of an ice-free season in the Arctic Ocean. The emergence of big waves in the Arctic could be bad news for operating in newly ice-free Northern waters.

“Almost all of the casualties and losses at sea are because of stormy conditions, and breaking waves are often the culprit,” Thomson said.

It also could be a new feedback loop leading to more open water as bigger waves break up the remaining summer ice floes.

“The melting has been going on for decades. What we’re talking about with the waves is potentially a new process, a mechanical process, in which the waves can push and pull and crash to break up the ice,” Thomson said.

Waves breaking on the shore could also affect the coastlines, where melting permafrost is already making shores more vulnerable to erosion.

The observations were made as part of a bigger project by a sensor anchored to the seafloor and sitting 50 meters (more than 150 feet) below the surface in the middle of the Beaufort Sea, about 350 miles off Alaska’s north slope and at the middle of the ice-free summer water. It measured wave height from mid-August until late October 2012.

Satellites can give a rough estimate of wave heights, but they don’t give precise numbers for storm events. They also don’t do well for the sloppy, partially ice-covered waters that are common in the Arctic in summer.

Warming temperatures and bigger waves could act together on summer ice floes, Thomson said: “At this point, we don’t really know relative importance of these processes in future scenarios.”

Establishing that relationship could help to predict what will happen to the sea ice in the future and help forecast how long the ice-free channel will remain open each year.

The recent paper recorded waves at just one place. This summer Thomson is part of an international group led by the UW that is to better understand the physics of the sea-ice retreat.

“There are several competing theories for what happens when the waves approach and get in to the ice,” Thomson said. “A big part of what we’re doing with this program is evaluating those models.”

He will be out on Alaska’s northern coast from late July until mid-August deploying sensors to track waves. He hopes to learn how wave heights are affected by the weather, ice conditions and amount of open water.

“It’s going to be a quantum leap in terms of the number of observations, the level of detail and the level of precision” for measuring Arctic Ocean waves, Thomson said.

The other author is W. Erick Rogers at the Naval Research Laboratory. The research was funded by the U.S. Office of Naval Research.

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For more information, contact Thomson at 206-616-0858 or jthomson@apl.washington.edu. He will be deploying sensors out of Prudhoe Bay from July 24 to Aug. 4 and have email access about once a day.