NASA last week that both the 91̽�� STRIVE team and the UW-affiliated EDGE team were selected to lead satellite missions to better understand Earth and improve capabilities to foresee environmental events and mitigate disasters.

STRIVE and EDGE were among four finalists as part of the agency’s Earth System Explorers Program, which conducts principal investigator-led space science missions as recommended by the National Academies of Sciences, Engineering, and Medicine 2017 Decadal Survey for Earth Science and Applications from Space.

The total estimated cost of each mission, not including launch, will not exceed $355 million with a mission launch date of no earlier than 2030, stated NASA.

“This was fantastic news. We have been working on this concept for a few years now, and for many of us it is a dream come true. To be able to observe the atmosphere at this level of detail is a tremendous opportunity,” said , a 91̽��professor of atmospheric and climate science, who is leading the STRIVE mission.

Stratosphere-Troposphere Response using Infrared Vertically-resolved light Explorer

, which stands for Stratosphere-Troposphere Response using Infrared Vertically-resolved light Explorer, will examine the regions of the atmosphere where weather forms and the ozone layer sits, yielding new insights into temperature and trace gases in the atmosphere that affect aviation, long-range transport of volcanic smoke and air pollution.

The STRIVE instruments, compact enough to fit into the trunk of a midsize SUV, can make more than 400,000 observations each day. Instead of looking straight down at the Earth, like other missions, the STRIVE instruments angle sideways towards Earth’s surface to capture the atmosphere in greater detail.

“With these observations, we won’t just get measurements of ozone but rather all the chemical species that affect ozone in the stratosphere,” Jaeglé said.

The ozone layer, which absorbs ultraviolet radiation, after severe depletion in the early 2000s, but still requires careful monitoring.

STRIVE represents a technological and scientific quantum leap that will help researchers understand how air pollution circulates following a wildfire or volcanic eruption, for example. Importantly, STRIVE will also aid weather forecasting efforts beyond the typical 10-day window to give people time to prepare for extreme weather events.

“If we can see something propagating from high up — such as large shifts in winds — then we will know that several weeks later it will impact Earth’s surface. Our current weather models cannot predict this connection very well because we don’t really know what is going on at the interface of the stratosphere and troposphere,” Jaeglé added.

The national-scale team includes partners from academia, industry and federal science labs. at the University of Iowa is the deputy principal investigator of STRIVE, and at NASA’s Goddard Space Flight Center is the project scientist. Several NASA Goddard scientists are also involved. Other 91̽��members of STRIVE are professor , assistant professor and affiliate faculty member , all in the 91̽��Department of Atmospheric and Climate Science.

The Earth Dynamics Geodetic Explorer 

, or Earth Dynamics Geodetic Explorer, uses lasers to observe the three dimensional structure of Earth’s surface — including forests, glaciers, ice sheets and sea ice — as it changes. , a senior principal physicist and , a senior research scientist both at the 91̽�� and , a 91̽��associate professor of civil and environmental engineering, are part of the EDGE team, led by from Scripps Institution of Oceanography at the University of California San Diego.

EDGE will be the first global satellite imaging laser altimeter system, according to . The system captures surface detail in high resolution by firing laser pulses at the Earth and recording how long it takes for them to return, making over 150,000 measurements each second. It can also precisely track changes in surface elevation over time to capture how ice sheets and glaciers are responding to climate change over seasonal and longer-term timescales.

“What’s really exciting about EDGE is the level of detail it will measure. Older laser altimetry measurements sample a coarse grid of points on the ground, but with the EDGE data we will be able to see individual trees around Seattle, and small cracks in glaciers in Greenland and Antarctica. Often, it’s the fine-scale processes that drive how the large-scale system changes,” Smith said.

Although the effort will focus on polar regions, forests and coastlines, EDGE is an “everything mission,” Shean said.

“These precise surface elevation change measurements are essential for so many pressing scientific and engineering applications,” he added. “The EDGE data will have implications for sea level rise, natural hazards monitoring, water resource and forest management, and wildfire response. This is also a major milestone for UW, as it formalizes 91̽��leadership and involvement on not one, but two NASA Earth Observation missions. I’m excited to bring students onto the EDGE team and train the next generation of 91̽��researchers who will do amazing things with EDGE data in the coming decades.”

For more information on STRIVE, contact Jaeglé at jaegle@uw.edu.

A project led by the 91̽�� to better understand our atmosphere’s complexity is a finalist for NASA’s next generation of Earth-observing satellites. The space agency this week the projects that will each receive $5 million to advance to the next stage and conduct a one-year concept study.

seeks to better understand the troposphere that we inhabit and the stratosphere above it, where the ozone layer is, as well as the interface where these two layers meet. That interface, about 6 miles (10 kilometers) above the surface, is where important atmospheric chemistry, circulation and climate processes occur.

In addition to STRIVE, two other teams among the finalists also include researchers from the UW.

The four teams that reached the proof-of-concept stage will spend the next year refining their proposals. NASA will then review the concept study reports and select two for implementation. Projects that reach the final stage will have a budget of up to $310 million to build the instruments, which NASA will launch into orbit in 2030 or 2032. The satellites are expected to have an initial working life of two to three years.

, professor of atmospheric sciences at the UW, is principal investigator of STRIVE, or “Stratosphere Troposphere Response using Infrared Vertically-Resolved Light Explorer.” The national-scale team includes partners from academia, industry and federal science labs.

The two instruments aboard the STRIVE spacecraft would observe temperature, ozone, water vapor, methane, reactive gases, smoke and other aerosol particles. They will collect 400,000 sets of observations every day — hundreds to thousands of times more than what’s possible now. Instead of looking straight down at the Earth, the STRIVE instruments point at an angle to Earth’s surface, allowing them to capture the atmospheric layers in greater detail.

These observations could help to monitor how the UV-absorbing ozone layer is rebuilding or deteriorating in the atmosphere; how smoke particles from volcanoes, wildfires or human emissions travel through the atmosphere and influence air quality; and how water vapor, ozone, and high-elevation clouds influence the climate system.

The STRIVE system would also support longer-range weather forecasts.

“Before a major weather event at the surface, there can be precursor signs that happen in the stratosphere,” Jaeglé said. “And we see those weeks ahead of time. Observing the stratosphere and how these signals propagate down will be key to getting better weather forecasts on subseasonal to seasonal scales, so two weeks to two months in advance.”

As several NASA satellites of their working lifetimes, the agency is looking for future possibilities to continue their legacy of tracking Earth’s changes.

“For observing the Earth, before we’ve had these multibillion-dollar instruments and platforms that take much longer to design and to put in operation. I think the overall idea is to move to a nimbler, faster set of satellite missions that will be designed more quickly and cost less,” Jaeglé said. “NASA will still pursue the bigger missions, but these smaller missions are another tool that they’re moving forward with.”

at the University of Iowa is the deputy principal investigator of STRIVE, and at NASA’s Goddard Space Flight Center is the project scientist. Several NASA Goddard scientists are also involved. Other 91̽��members of STRIVE are professor , assistant professor and affiliate faculty member , all in the 91̽��Department of Atmospheric Sciences.

Other institutions include the Pacific Northwest National Laboratory, the Lawrence Livermore National Laboratory, the National Center for Atmospheric Research, NorthWest Research Associates, Science Systems and Applications, NASA’s Goddard Institute for Space Studies, the University of Colorado-Boulder, the University of Toronto and Morgan State University.

The STRIVE team will spend the next year developing a report with an in-depth engineering, cost and technical analysis.

“It’s extremely exciting. This was a team effort, with many people involved,” Jaeglé said. “Also a bit daunting because the next year will be a very busy one, but very exciting for how to make these concepts become a reality.”

Two other projects among the four finalists also involve 91̽��scientists

The proposal, led by the University of California, San Diego, proposes a new laser instrument to measure the height of vegetation, glaciers and polar ice sheets.

“The current state-of-the-art for satellite laser altimetry, the satellites that measure surface height, is ICESat-2, which has six laser beams. GEDI, on the International Space Station, has eight beams. EDGE will have 40 laser beams, so the level of detail is just much, much higher,” said , a research scientist at the 91̽��Applied Physics Laboratory who’s a member of the ICESat-2 science team and is an investigator on the EDGE proposal.

The EDGE satellite would collect data for the world’s forests with the ability to resolve individual trees. Unlike existing satellites it would span all latitudes, from the boreal forests to the equator, surveying dense rainforests to sparser temperate woodlands. EDGE would also observe polar ice sheets and glaciers worldwide, including in the Western U.S., Alaska and the Himalayas, where populations rely on meltwater for hydropower, agriculture and household use.

“It’s very nimble, so it can be off-pointed to collect very dense 3D measurements over priority areas,” said , a 91̽��assistant professor of civil and environmental engineering who is also involved with EDGE. “So for example, we could scan the entire Nisqually Glacier on Mount Rainier, and potentially many other Pacific Northwest glaciers, in a single pass.”

STRIVE science team member Alex Turner is also a member of the proposal led by CalTech and NASA’s Jet Propulsion Laboratory. Carbon-I would sample carbon dioxide and methane gases, tracking both emissions and sinks in places like the Amazon rainforest. It would have a global resolution of 300 meters, or about the length of three football fields, and could zoom in to a resolution of just 100 feet (30 meters) to investigate particular sources.

“We suspect that for methane in particular there are ‘superemitters,’ or a small number of sources that emit massive amounts of methane,” Turner said. “From a regulatory perspective, if you can find and fix those superemitters in a timely manner, you can cut your emissions by a pretty large amount.”

The awards are part of NASA’s new Earth System Explorers Program. The other finalist proposal is , led by the University of California, San Diego.

“As we continue to confront our changing climate, and its impacts on humans and our environment, the need for data and scientific research could not be greater,” said Nicky Fox, associate director at NASA headquarters. “These proposals will help us better prepare for the challenges we face today, and tomorrow.”

For more information on STRIVE, contact Jaeglé at jaegle@uw.edu.

Less than three months into its mission, NASA’s Ice, Cloud and land Elevation Satellite-2, or , is already exceeding scientists’ expectations, to the space agency. The satellite is measuring the height of sea ice to within an inch, tracing the terrain of previously unmapped Antarctic valleys and measuring other interesting features in our planet’s elevation.

, a glaciologist with the 91̽�� and , shared the first look at the satellite’s performance at the American Geophysical Union’s annual meeting Dec. 11 in Washington, D.C.

Mountain valleys “have been really difficult targets for altimeters in the past, which have often used radar instead of lasers and they tend to show you just a big lump where the mountains are,” Smith . “But we can see very steeply sloping surfaces; we can see valley glaciers; we’ll be able to make out very small details.”

With each pass of the ICESat-2 satellite, the mission is adding to the data sets that track Earth’s rapidly changing ice. Researchers are ready to use the information to study sea level rise resulting from melting ice sheets and glaciers, and to improve sea ice and climate forecasts.

In topographic maps of the Transantarctic Mountains, which divide east and west Antarctica, there are places where other satellites cannot see, Smith said. Some instruments don’t orbit that far south, while others only pick up large features or the highest points and so miss minor peaks and valleys. Since launching ICESat-2, in the past three months scientists have started to fill in those details.

“It’s spectacular terrain,” Smith said. “We’re able to measure slopes that are steeper than 45 degrees, and maybe even more, all through this mountain range.”

As ICESat-2 orbits over Antarctica, the photons reflect from the surface and show high ice plateaus, crevasses in the ice 65 feet (20 meters) deep, and the sharp edges of ice shelves dropping into the ocean. These first measurements can help fill in the gaps of Antarctic maps, Smith said, but the key science of the ICESat-2 mission is yet to come. As researchers refine knowledge of where the instrument is pointing, they can start to measure the rise or fall of ice sheets and glaciers.

Early data suggest that Antarctica’s Dotson ice shelf (120 meters) in thickness since 2003, Smith told the Associated Press.

“Very soon, we’ll have measurements that we can compare to older measurements of surface elevation,” Smith said. “And after the satellite’s been up for a year, we’ll start to be able to watch the ice sheets change over the seasons.”

Mission managers expect to release the data to the public in early 2019.

The first ICESat satellite operated between 2003 and 2009. The more sophisticated ICESat-2 launched Sept. 15, 2018, from Vandenberg Air Force Base in California. Its laser instrument, called ATLAS (Advanced Topographic Laser Altimeter System), sends pulses of light to Earth. The instrument then times, to within a billionth of a second, how long it takes individual photons to return to the satellite. ATLAS has fired its laser more than 50 billion times since going live Sept. 30, and all the metrics from the instrument show it is working as it should, NASA scientists say. IceBridge, an aircraft-based NASA campaign, operated between the two satellite missions.

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For more information, contact Smith at besmith@uw.edu or 206-616-9176.

Adapted from a NASA .

NASA plans to launch a new satellite this month that will measure elevation changes on Earth with unprecedented detail. Once in the air, it will track shifts in the height of polar ice, mountain glaciers and even forest cover around the planet.

Two 91̽�� polar scientists are advising the mission scheduled to launch Sept. 15 from California’s Vandenberg Air Force Base. 91̽��researchers provided expertise in two areas of intense interest for long-term tracking: massive glaciers covering Antarctica and Greenland, and sea surface height in the Arctic and other oceans.

“ICESat-2 is designed to answer a simple glaciology question very, very well: It will tell us where, and how fast, the ice sheets are thickening and thinning,” said , a glaciologist at the UW’s Applied Physics Laboratory. “When these data start coming in we will immediately get a big-picture map of how Antarctica and Greenland have changed over the past decade.”

Smith is a member of the science definition team and the lead author of the document that describes the data that ICESat-2 will provide for ice that covers land.

“My specific role is to work out how to turn the raw data that NASA generates — which track the location of individual photons — into the answer we want to give the scientific community, which is how high the ice sheet surface is at a particular point,” Smith said.

The instrument, whose full name is the Ice, Cloud, and Land Elevation Satellite, succeeds the original ICESat-1 satellite that operated from 2003 to 2009. Since then NASA has been running annual flights to collect data over a few important parts of Antarctica and Greenland during the gap. The new satellite will provide nonstop, higher-resolution data for the Earth sciences community starting this October, one month after it launches.

“For me, the most exciting aspect of ICESat-2 is its extremely fine resolution,” said , a polar oceanographer and former leader of the North Pole Environmental Observatory. The new satellite uses six laser beams to get readings every 2-3 feet, each one focused over a 30-foot patch of the surface. For comparison, Morison said, today’s instruments measure surface elevation by averaging over many hundreds of feet to miles between each data point. The new instrument’s orbit is designed to collect more data over the poles, and it can detect very small elevation changes over long timescales.

Morison is a physical oceanographer on the science definition team, and lead author the document that describes ICESat-2 data for the open oceans.

“For the oceans, ICESat-2 will yield fine-scale measurements that are important to coastal oceanography, revealing smaller features in the open ocean and even down to the characteristics of larger surface waves,” Morison said. “ICESat-2 will also help measure sea-level change, particularly at high latitudes where the most established radar altimeters don’t go, and it will give us higher-resolution measurements of the sea surface slopes that drive changing ocean circulation.”

The two 91̽��researchers were members of a 12-person that consulted on the project over the years leading up to the launch. They also are among the hundreds of scientists who anticipate using the data in their research.

“ICESat-2 observations will make it possible to study glaciers that are too remote for aircraft to reach, and it will make it possible to detect small changes over large areas, which were difficult to see clearly with older data,” Smith said. “There are a lot of places in Antarctica where we assume that not much is happening, but we don’t have great evidence one way or another. My guess is that when we look carefully, there will be a lot to see.”

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For more information, contact Smith at besmith@uw.edu or 206-616-9176 and Morison at jhm2@uw.edu or 206-543-1394. More ICESat-2 multimedia is .

They will be available in Seattle until Thursday, Sept. 13, when they will travel to California for Saturday’s anticipated launch.

But the details of its collapse remain uncertain. The details are necessary to provide a timeline for when to expect 2 feet of global sea level rise, and when this glacier’s loss will help destabilize the much larger West Antarctic Ice Sheet. Recent efforts have used satellites to map the underlying terrain, which affects how quickly the ice mass will move, and measure the glacier’s thickness and speed to understand the physics of its changes.

Researchers at the 91̽�� and the University of Edinburgh used data from the European Space Agency’s CryoSat-2 to identify a sudden drainage of large pools below Thwaites Glacier, one of two fast-moving glaciers at the edge of the ice sheet. The published Feb. 8 in The Cryosphere finds four interconnected lakes drained in the eight months from June 2013 and January 2014. The glacier sped up by about 10 percent during that time, showing that the glacier’s long-term movement is fairly oblivious to trickles at its underside.

“This was a big event, and it confirms that the long-term speed-up that we’re observing for this glacier is probably driven by other factors, most likely in the ocean,” said corresponding author , a glaciologist with the UW’s Applied Physics Laboratory. “The water flow at the bed is probably not controlling the speed.”

Other glaciers, like some in Alaska and Greenland, can be very susceptible to changes in meltwater flow. Water there can pond beneath the glacier until it lifts off parts of its bed, and suddenly surges forward. This can increase a glacier’s speed by several times and account for most of its motion.

Researchers were not certain whether such an effect might be at play with Thwaites Glacier.

“It’s been difficult to see details about water flow under the ice,” Smith said.

For the new study, the authors use a new technique to discover drops at the glacier’s surface of up to 70 feet (20 meters) over a 20 kilometer by 40 kilometer area. Calculations show it was likely due to the emptying of four interconnected lakes, the largest about the size of Lake Washington, far below. The peak drainage rate was about 8,500 cubic feet (240 cubic meters) per second, about half the flow of the Hudson River — the largest meltwater outflow yet reported for subglacial lakes in this region.

“This lake drainage is the biggest water movement that you would expect to see in this area, and it didn’t change the glacier’s speed by that much,” Smith said.

The reason is likely that Thwaites Glacier is moving quickly enough, he said, that friction is heating up its underside to ice’s melting point. The glacier’s base is already wet and adding more water doesn’t make it much more slippery.

The new study supports previous 91̽��research from 2014 showing that Thwaites Glacier to cause seas to rise by 2 feet. Those calculations were made without detailed maps of how water flows at the glacier’s underbelly. The new results suggest that doesn’t really matter.

“If Thwaites Glacier had really jumped in response to this lake drainage, then that would have suggested that we need a more detailed model of where water is flowing at the bed,” Smith said. “Radar data from NASA’s Operation Ice Bridge program has told us a lot about the shape of Thwaites Glacier, but it’s very difficult to see how water is moving. Based on this result, that may not be a big problem”

Melting at the ice sheet base would refill the lakes in 20 to 80 years, Smith said. Over time meltwater gradually collects in depressions in the bedrock. When the water reaches a certain level it breaches a weak point, then flows through channels in the ice. As Thwaites Glacier thins near the coast, its surface will become steeper, Smith said, and the difference in ice pressure between inland regions and the coast may push water coastward and cause more lakes to drain.

He hopes to apply the same techniques to study lake drainage below other glaciers, to understand how water flow at the base affects overall glacier movement. When NASA’s ICESat-2 satellite launches in 2018 the calculations will be easy to do with high precision.

“In 2018 this changes from a hard project to an easy project, and I’m excited about that,” Smith said.

Other co-authors are and at the 91̽��and at the University of Edinburgh. The research was funded by NASA and the European Space Agency.

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For more information, contact Smith at bsmith@apl.washington.edu or 206-616-9176.

See also University of Edinburgh .

NASA grants: NNX13AP96G, ANT0424589

‘Hurricane hunter’ measures polar vortex

A long-planned mission researchers had feared could be finally left in late October. , a research meteorologist at the Joint Institute for the Study of the Atmosphere and Ocean, returned from 2 1/2 weeks in Alaska as part of a trip to measure how less ice and more open water in the Arctic Ocean might influence storm paths.

The partnership between the 91̽��and the National Oceanic and Atmospheric Administration used NOAA’s “hurricane hunter” aircraft to and see how heat radiating off the surface could destabilize the polar vortex, a huge weather feature that can affect storms throughout the Northern Hemisphere.

“When the polar vortex is strong, it’s very stable,” Bond said. “It’s like a Frisbee spinning fast – it’s stable and the cold air that develops in the Arctic is kind of bottled up.”

When the polar vortex is weaker, however, wobbles can send cold air shooting south. That’s when places like New York City, Washington, D.C., Northern Europe and Eastern Asia get hit with snowstorms and wintry weather.

Some scientists have suggested that an ice-free Arctic Ocean could destabilize the polar vortex. The mission collected data to help test this controversial theory, Bond said.

The measurements meant flying just 200 feet above the surface, and it often felt closer than that, Bond said. The specialized aircraft was equipped with more instruments than most weather stations to collect detailed measurements of heat and air turbulence.

In coming months, Bond and his colleagues will analyze the data and compare the observations with output from weather forecasting and climate models. They hope to understand whether the extra heat from the open water is enough to destabilize the polar vortex. Also of interest is how well weather-forecasting and ice models can predict conditions in the Chuchki Sea northwest of Alaska, an area now being explored for its oil.

The 16-day federal shutdown delayed the mission, but unseasonably warm weather meant the team was taking measurements at the right time to capture the fall freeze-up, Bond said.

“We were just fortunate, and it actually worked out pretty well,” he said.

Measuring summer glacier melt

Also this month, 91̽��researchers helped the National Aeronautics and Space Administration create laser maps of melting Greenland glaciers. , a geophysicist with the 91̽��Applied Physics Laboratory, helped design flight paths for the 16-day that ended Saturday (Nov. 16).

Scientists hope to better understand glaciers, the wild card in terms of climate change and rising sea levels. A NASA research aircraft used lasers to make an elevation-change map for important parts of the Greenland ice sheet.

Smith will compare the new data with similar measurements taken last spring to calculate how much the surface melted during the summer. This first-ever fall measurement will provide a baseline estimate of summer melt, in preparation for year-round laser monitoring of glaciers set to begin in 2016.

“Jakobshavn Glacier is the most exciting glacier in Greenland right now because it’s losing tremendous amounts of mass into the ocean,” Smith said. Flight paths included measurements right at the foot of the glacier, where ice is lost both to melting and to icebergs calving, and higher up on the ice sheet in colder conditions.

The government shutdown delayed the flight and some snow had already accumulated on the glacier. Another consequence was the temperatures – flights conducted by NASA scientists were very cold, Smith said.

UW–Coast Guard monitoring flights

Also under way this month is the last installment this year in a series of flights in which 91̽��Applied Physics Laboratory on flights out of Kodiak, Alaska to drop oceanographic probes into cracks in the sea ice and deploys buoys in tough-to-reach Northern waters.

, an oceanographer at the Applied Physics Lab, leaves Tuesday (Nov. 19) for his first such flight in three months. This will be the latest in the year that the 40-year veteran of Arctic research has ever been out on the ice.

“With the limited daylight, finding open water for our sensor drops will be challenging,” Morison said.

The ocean current and temperature observations help 91̽��researchers, the National Snow and Ice Data Center and others to monitor and understand changing Arctic conditions.

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For more information, contact Bond at 206-526-6459 or nab3met@uw.edu; Smith at 206-616-9176 or bsmith@apl.washington.edu and Morison at 206-543-1394 or morison@apl.washington.edu.

Pictures of the NOAA trip:

NOAA news release: “”������������������������������������������������������

NASA news release: ““

Dozens of climate scientists have reconciled their measurements of ice sheet changes in Antarctica and Greenland during the past two decades. The results, published Nov. 29 in the journal , roughly halve the uncertainty and discard some conflicting observations.

“We are just beginning an observational record for ice,” said co-author , a glaciologist in the 91̽��’s Applied Physics Laboratory who is lead author on an accompanying review article. “This creates a new long-term data set that will increase in importance as new measurements are made.”

The examined three methods that had been used by separate groups and established common places and times, allowing researchers to discard some outlying observations and showing that the results agree to within the uncertainties of the methods.

“It provides a simpler picture,” said co-author , a research scientist at the UW’s Applied Physics Laboratory. “In the 1990s, not very much was happening. Sometime around 1999, the ice sheets started losing more mass, and probably have been losing mass more rapidly over time since then.”

The effort, led by Andrew Shepherd at the University of Leeds in the UK, reconciles three existing ways to measure this loss. The first method takes an accounting approach, combining climate models and observations to tally up the ice gain or loss. Two other methods use special satellites to precisely measure the height and gravitational pull of the ice sheets to calculate how much ice is present.

Each method has strengths and weaknesses. Until now scientists using each method released estimates independent from the others. This is the first time they have all compared their methods for the same times and locations.

“It brought everyone together,” Joughin said. “It’s comparing apples to apples.”

Since 1998, scientists have published at least 29 different estimates of how much ice sheets have contributed to sea-level rise, ranging from 1.9 mm (0.075 inches) a year to 0.2 mm (0.0079 inches) drop per year. The new, combined estimate is that ice sheets have since 1992 contributed on average 0.59 mm (0.023 inches) to sea-level rise per year, with an uncertainty of 0.2 mm per year. Overall sea levels have risen by about 3.3 mm per year during that time period, much of which is due to expansion of warmer ocean waters.

“Establishing more consistent estimates for the contribution from ice sheets should reduce confusion, both among the scientific community and among the public,” Joughin said.

Understanding why the ice sheets have been shedding mass faster in the last decade is an area of intense research. The accelerated ice loss was not predicted by the models, leading the latest Intergovernmental Panel on Climate Change report to place no upper limit on its estimate for future ice-sheet loss.

Joughin is lead author of an that reviews factors that cause ice sheets to lose more mass. In particular, it looks at what happens when warmer ocean waters reach the underside of large floating Antarctic ice sheets or abut glaciers in Greenland’s fjords.

Joughin and his co-authors, Richard Alley of Pennsylvania State University and David Holland of New York University, suggest ways to better monitor and understand those changes: Create finer-grained ocean models that could include narrow fjords, develop more models to study the interaction between ice sheets and ocean water, and improve ice sheet monitoring.

Taking measurements at ice edges is perilous, they write, because skyscraper-sized chunks of ice can topple on floating instruments with no notice, and outgoing glaciers can scour any instruments moored to the ocean floor.

Understanding ice sheets is central to modeling global climate and predicting sea-level rise. Even tiny changes to sea level, when added over an entire ocean, can have substantial effects on storm surges and flooding in coastal and island communities.

The West Antarctic Ice Sheet could trigger abrupt changes globally if it were to become unstable, and although Greenland is thought to be more stable, the recent calving of glaciers has led to some alarm.

Joughin believes the recent activity is a reason to pay attention, but not to panic.

“We don’t fully understand why it’s accelerating,” Joughin said. “But the longer-term observations we have, the more solid predictions we will be able to make.”

The 91̽��portions of the research were funded by the National Science Foundation and the National Aeronautics and Space Administration.

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For more information, contact Joughin at 206-221-3177 or ian@apl.washington.edu and Smith at 206-616-9176 or bsmith@apl.washington.edu.