‘Foreign Policy’ Salutes the Cryosphere

Last month, a Foreign Policy column focused on security issues turned its attention to the cryosphere.

The writer, Sharon Burke, a senior advisor at the New America foundation and former Obama administration official, began by pointing out the “aesthetic pleasure” of the term “cryosphere”:

The word sounds like some kind of secret realm, possibly involving dead people, but it’s really ice, snow, glaciers, and permafrost. The cryosphere is all the frozen places on Earth, or more specifically, all the frozen water on Earth.

There’s just one problem with the magical ice kingdom: It’s melting.

Burke then focused on a new study (the New York Times covered it in late March) about the Antarctic ice sheet, and the implications that could have for the billions who live in places where the waters will rise.

According to the study, published in the journal Nature in March 2016 and called “Contribution of Antarctica to past and future sea-level rise,” the Antarctic ice sheet is melting at a much faster rate than previously thought. This melting ice ends up in the Earth’s oceans, contributing to sea level rise.

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Effect of Southern Ocean warming on Antarctic surface air temperatures and the ice sheet at 128 kyr ago (Photo: Robert M. DeConto, David Pollard )

The study uses updated modeling, which includes details about rocks and glaciers, to establish projections of future Antarctic ice sheet loss. The authors say that if greenhouse gas emissions continue to grow, the West Antarctic ice sheet will start to break apart by the year 2050. The model includes melting from both below and above the ice sheets, by including the impact from warmer ocean currents underneath ice sheets and warmer temperatures in the atmosphere. The improved model reproduced ancient historical sea levels more accurately than previous models, focusing on a period  125,000 years ago, when the oceans were 20 to 30 feet higher. This success supports the model’s ability to accurately predict future sea levels.

But the Antarctic ice sheet is not the only factor influencing sea level. Sea ice, land glaciers, and permafrost are also melting at a rate that contributes to the disappearance of the cryosphere and contributing to rising oceans.

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Components of the cryosphere and their time scales. (Photo: IPCC )

Sea level rise is a very large problem for the human populations located in the vulnerable coastal zones. The Times article points out that New York, a city founded roughly 400 years ago, is unlikely to remain intact for the next 400 years. Cities like Miami, London, Hong Kong, and Sydney are also likely to feel the rising tides. But the populations in the most danger are those outside in the developing world. Dhaka, the capital of Bangladesh, provides an example. It is one of the most populated cities in the world, with 15 million people, and is located at sea level.

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Flooding is already common in Dhaka (Photo: flickr/masud ananda)

According to the study, the collapse of the Antarctic ice sheet could mean more than three feet of sea level rise, leaving limited alternatives for populations at risk. Costly solutions like sea walls and augmented infrastructure are out of the reach of the poorest cities. This leaves them in the greatest danger, with few options.

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New Study Warns: Rapid Sea Level Rise, Superstorms Likely

Existing climate change assessments could be underestimating the amount of future sea level rise, as well as the likelihood of other phenomenons like increased superstorms and glacier loss, warns a new high-profile paper in Atmospheric Chemistry and Physics. The study, by longtime climate scientist James Hansen and 18 co-authors, has gained attention recently for its radical projections of climate change impacts.

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Photo: Dr. James Hansen

To conduct research for the paper, titled Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2 ◦C global warming is highly dangerous, Hansen and the other authors combined ancient climate data with new satellite readings and an updated climate model to show that ice melt is occurring more quickly than previously thought. Instead of incrementally melting, the ice sheets around the Earth’s poles actually melt at a non-linear rate, losing mass rapidly, according to Hansen and his team.

“We have uncovered information and a partial understanding of feedbacks in the climate system, specifically interactions between the ocean and the ice sheets. These feedbacks raise questions about how soon we will pass points of no return, in which we lock in consequences that cannot be reversed on any time scale that people care about. Consequences include sea level rise of several meters, which we estimate would occur this century or at latest next century, if fossil fuel emissions continue at a high level,” Hansen says in a video released about the paper. “That would mean loss of all coastal cities, most of the world’s large cities and all their history.”

Hansen notes that a positive feedback loop is created as ice melt influences the structure of the ocean’s layers. As cold freshwater runoff from exit glaciers flows into the ocean, it lowers the density of the surface water. This change of density shuts down the normal circulation in which cold salty water sinks and brings warm water to the surface, releasing the heat it carries into the atmosphere. But when heat stays in the ocean at a depth where ice shelves contact the trapped warm water, a feedback loop occurs. The warm water next to the deep ice makes the ice melt even faster.

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Stratification and precipitation amplifying feedbacks. Source: Hansen et al, 2015

Thus the ice melt in these regions causes further loss of ice sheets in direct contact with the ocean, which contributes to more rapid movement of exit glaciers and to faster sea level rise. In addition to quickening ice melt, the feedback loop also contributes to shutting down the ocean’s circulation, trapping warm water between layers of cold water in polar regions. The feedback loop creates a greater temperature gradient by increasing temperature differences between high and low latitudes, which increases the likelihood of superstorms.

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Source: 5 Meters of sea level rise

Earth’s ice sheets are melting quickly, and the rate of melt is also expected to increase exponentially. As a result, we could see the sea level rise up to five meters, or about 16 feet, by the end of this century if no emissions reduction actions are taken. This puts many of the world’s coastal cities in danger of flooding, including cities like Miami, London, New York, Miami and Shanghai.

The paper forecasts a greater increase in sea level within a shorter period of time than other research has found. In its 2013 Fifth Assessment Report (AR5), the U.N’s Intergovernmental Panel on Climate Change (IPCC) predicts closer to three feet of sea level rise occurring at or after 2100.

“The models that were run for the IPCC report did not include ice melt,” Hansen said at a news conference.

But the paper has received criticism. Hansen and the other researchers first released their research as a discussion paper in the European Geosciences Union (EGU) Open Access journals. This made the paper visible to the public before the peer review process was finished, which is atypical of scientific research and generated some criticism.

There has been contention about Hansen findings within the scientific community, which can be seen not only in the papers reviews and comments but also playing out across Twitter and in the news. In an op-ed on the paper in the New York Times, the environmental journalist Andy Revkin quoted  the climate journalist Eric Holthaus, who succinctly sums up the negative responses in the tweet, appended below.

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Gravity satellite ice sheet mass measurements for greenland and antarctic ice sheets. Photo: Hansen

Concern has been expressed that the predictions made in the paper are too extreme. For one, some critics found the assumptions, such as exponential rates of ice loss, to be improbable. Others raised objections to the particular way in which paleoclimate data was used to suggest future conditions. Kevin Trenberth of the National Center for Atmospheric Research strongly criticized the study, saying that “there are way too many assumptions and extrapolations for anything here to be taken seriously other than to promote further studies.” As the extensive comments on blog posts here and here show, the paper by Hansen and his team has attracted a great deal of attention, and sparked lengthy debates in the scientific community.

At a February 2012 TED talk titled Why I must speak out about climate change Hansen said: “Clearly I haven’t got this message across. The science is clear. I need your help to communicate the gravity and urgency of this situation and its solutions more effectively. We owe it to our children and grandchildren.”

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Life on the Edge: The Science of Glaciers that Meet Oceans

Tidewater glacier on Antarctic coast (source: Jason Auch/Flickr)
Tidewater glacier on Antarctic coast (source: Jason Auch/Flickr)

In an October 2015 article in Earth & Space Science News, David Holland and Denise Holland suggest steps to increase the understanding of glacier melt to improve projections of sea level rise.

IPCC (Intergovernmental Panel on Climate Change) reports have concluded that anthropogenic causes are to blame for glacier retreat in the last century. They predict that increased melt in the present century will rise global sea levels. The authors report that the contribution of the West Antarctic Ice Sheet, alone will change low-lying coastal and communities worldwide and threaten marine ecosystems.

They note that the rate of sea level rise will be influenced by a number of factors, including the local shifts in the gravitational pull of land masses, along with changes in water currents, wind patterns, and water temperature and salinity. The rebound of land masses, once the weight of glaciers and ice sheets is removed, will also influence sea levels.

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Map of Antarctica (source: Maximilian Dörrbecker [Chumwa])
The complex nature of the interface between ice sheets and the ocean also creates uncertainty about the future of many of the West Antarctic glaciers, as it is difficult to make predictions of how the ice will react in the future. In one possible scenario, the circulation of warm ocean waters that is currently held off by continued cold meltwater runoff from Antarctica could grow larger, and the cold water barrier would no longer block it from teaching the continent. The warm water would thus be able to make direct contact with the underside of the glacier and warm it from below, greatly increasing the glacier melt.

Holland and Holland note that many problems with predicting the effects of West Antarctic glacier melt stem from a deficit of data. Though satellites are able to measure glacier volume, they are unable to observe the water resting underneath glaciers or the land mass upon which some glaciers rest. Another area of difficulty in predicting the melting of the West Antarctic glacier involves a shortfall in scientific understanding of calving—the process in which the section of a glacier front breaks and falls into the ocean. Scientists compare the difficulties of constructing models of calving to the challenges of predicting earthquakes. They remain unable to make long-term predictions about when they will occur.

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Sketch of the Antarctic coast showing interactions of ice sheet, glaciers and oceans. (Source: Hannes Grobe, Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany )

Holland and Holland state that in order to create accurate predictions for the contributions of the West Antarctic Ice Sheet to sea level rise, scientists need to couple glacier and ocean models. Currently there is little cooperation between glaciologists and oceanographers, even though both work on sea level rise since each uses separate models specific to their disciplines. To address this problem Holland and Holland report, the World Climate Research Programme (WCRP) has established a project, Climate and Cryosphere (CliC). This project held a meeting in October 2014, in which the Marine Ice Sheet–Ocean Model Intercomparison Project (MISOMIP) was established. The project seeks to draw on the efforts glaciological and oceanographic modelers. The participants in the project work together to create coupled and interactive glacier-ocean models. The goal is to follow this suite of glacier-ocean models with regional simulations of specific outlet glaciers such as those found in West Antarctica.

Holland and Holland say that scientists, by coupling glacier and ocean models, can greatly improve the accuracy of future sea level rise projections attributed to the West Antarctic Ice Sheet and its outlet glaciers. Because of the increasing threat of sea level rise to communities around the world, the accuracy of such projections is of great value. It is to be hoped that this importance will support efforts to produce these projections, which require increased cooperative effort between nations and between disciplines.

 

 

 

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Glacier Dynamics May Not be Fully Understood

Jakobshavn Isbræ, an outlet glacier off the west coast of Greenland, is losing mass faster than previously thought, due to increased melt water passing through it, as reported in a new paper. The glacier’s rapid trajectory of thinning may well represent the Greenland Ice Sheet (GrIS) ice loss rate in the near future, which could mean faster sea level rise than currently projected.

 

A team of researchers affiliated with the IMAU developed models of  the glacier’s dynamics, and ran 50 tests of these models with different sets of parameterizations such as ocean temperature, ice mass and basal melt until they were able to best match the models with the observed acceleration of Jakobshavn Isbræ. These parameters were then put in place to run the rest of the research. The 2012 acceleration was not captured by the models because it was an exceptional warm melt season that exceeded the mean length of the melt seasons of the previous 20 years; this season caused an exceptionally large amount of meltwater to pass through Jakobshavn Isbræ.

“An intense and long melt year leads to strong thinning of the ice, steepening surface slopes, and has the potential to further sustain the initial acceleration of [Jakobshavn Isbræ],” the authors wrote in their paper. Extreme warming events “may have created the conditions under which the winter slowdowns can no longer compensate for the summer accelerations leading to an increase in the mean annual flow,” they added.

 

Jakobshavn Isbræ calving front
Jakobshavn Isbræ calving front

The acceleration of the ice mass loss of Jakobshavn Isbræ was modelled by 3D representations of the glaciers. There were two known accelerations in the distant past, in 1998 and 2004. The 2003-04 observed event was so intense that the models were unable to represent the amount of mass loss that it sustained. The floating tongue of Jakobshavn Isbræ was ultimately thinned to the point of collapse in the 2003 acceleration event; this collapse led to even more thinning and increased mass loss.

The floating tongue of a glacier provides a terminus point and helps stabilize the glacier. Once a glacier begins to erode to the floating tongue, the acceleration tends to increase and there is even more mass loss than before the break up. (Further explanations of glacier terms can be found here.)

“Findings suggest that the speed observed today at [Jakobshavn Isbræ] is a result of thinning induced changes and a reduction in resistive stress (buttressing) near the terminus correlated with inland steepening slopes,” the authors wrote.

Jakobshavn Isbræ is an important indicator of future sea level rise since it is the largest drainage outlet glacier from the GrIS. It has seen a doubling in acceleration of mass loss and melt water velocity which shows the GrIS is experiencing higher than normal melt seasons.

Jakobshavn Isbræ ice loss and retreat
Jakobshavn Isbræ ice loss and retreat

Due to constraints of typical global models to represent the increased acceleration of ice flow over outlet glaciers during warming events, there is an underestimation of this ice flow’s contribution to overall sea level rise. Increased acceleration of the Jakobshavn Isbræ may be an important piece of the puzzle to help scientists more accurately portray sea level rise in their global models.

This research points to the importance of replicating such analysis in other regions. Other GrIS drainage areas have seen a recent slowdown of ice melt, so this finding may be confined only to one area. However, Jakobshavn Isbræ’s status as the largest of the drainage areas suggests that it may well provide a kind of climatological foreshadowing of future events. According to the authors, climate modelers need to better incorporate the dynamics of glacier mass loss acceleration into their models to better represent potential sea level rise.

 

GRIS ice discharge 1 from AMAP on Vimeo.

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The Sound of Glacial Calving

Listening to the unique creaks and cracks of an arctic fjord, six researchers affiliated with the Polish Academy of Sciences recorded the sounds glaciers make as they break off into water. The recordings are being used in an important effort to better understand this process of breaking off, called calving.

Glacial calving is “poorly understood” according to the researchers who published a new article in the scientific journal, Geophysical Research Letters, titled, Underwater acoustic signatures of glacier calving. However, through their research they successfully identified three distinct ways that glaciers calve, typical subaerial, sliding subaerial, and submarine. Basically, whether the piece of ice breaking off was falling outward from the top of the glacier, like a person jumping off the top, sliding straight down the face of the glacier, like something very slowly sliding off the top, or was actually breaking off underwater and shooting up to the surface, like a person swimming back up after falling in.

An image of three types of glacial calving and their sound signatures.
Types of glacial calving from Glowacki et. al, 2015.

Although glaciers around the world, by definition, are all large masses of ice that last year-round and slowly move, they vary in size, shape, speed, and importantly, location. Eventually, many glaciers terminate at bodies of water. Glaciers that terminate at bodies of water with tidal patterns, like oceans fjords, and sounds, are called tidewater glaciers. Tidewater glaciers are a form of calving glaciers, which break off into chunks as they push forward into bodies of water, creating icebergs.

This new article adds to our understanding of this process in a novel way. By recording the sounds of the calving process the researches overcame previous obstacles in monitoring these events. In the past, keeping track of tidewater glacial calving was difficult due to the lack of sunlight in the poles and the poor quality of satellite imagery. However, using relatively cheap and simple underwater microphones, called hydrophones, attached to a buoy, the researches identified the distinct sound signatures of the ice slowly melting, cracking and expanding, and eventually, breaking off from the glacier altogether. The researchers then combined the calving sound signatures with photographs from a GoPro camera they had set up to monitor the events visually, allowing them to identify and confirm the three distinct types of calving.

They say that by continuing to monitor the underwater sounds glaciers make, scientists will be able collect more data on how, and how much, glaciers around the world are breaking off into the bodies of water in which they terminate. This will help to better understand the calving process itself, as well as allow them to keep better track of how quickly glaciers are melting due to climate change.

This is important, because tidewater glaciers contribute more water to global sea level rise than any other type of glacier, and by some counts, contribute more water to sea level rise than the Antarctic and Greenland Ice Sheets combined.

By establishing the connection between the visual and audio information the researches established that these sound signatures did in fact correspond to these particular types of events, and presumably, could be used on its own in the future– giving scientist a cheap and easy monitoring tool to gauge glacier calving around the world.

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Earthquakes Rattling Glaciers, Boosting Sea Level Rise

An iceberg from the Helheim Glacier in calm waters, Sermilik fjord, East Greenland. ©  Mads & Trine
An iceberg from the Helheim Glacier in calm waters, Sermilik fjord, East Greenland.
© Mads & Trine

Talk of earthquakes likely calls to mind giant fissures opening up along the earth’s crust, the trembling of rock, buildings crumbling to their knees and, depending on your age and cast of mind, the love of Superman for Lois Lane. But it does not likely conjure up images of giant tongues of sliding ice or the splash of calving icebergs. And yet it should.

Most earthquakes are generated by the friction produced by two bodies of rock rapidly sliding past each other on a fault in the Earth’s crust, but a different breed of earthquakes was discovered in 2003: glacier earthquakes.

Map showing 252 glacial earthquakes in Greenland for the period 1993–2008, detected and located using the surface-wave detection algorithm. (b) Map showing the improved locations of 184 glacial earthquakes for the period 1993–2005 analyzed in detail by Tsai Ekström (2007). ©  Glacial Earthquakes in Greenland and Antarctica, Meredith Nettles and Göran Ekström, Lamont-Doherty Earth Observatory of Columbia University
Map showing 252 glacial earthquakes in Greenland for the period 1993–2008, detected and located using the surface-wave detection algorithm. (b) Map showing the improved locations of 184 glacial earthquakes for the period 1993–2005 analyzed in detail by Tsai Ekström (2007). © Glacial Earthquakes in Greenland and Antarctica, Meredith Nettles and Göran Ekström, Lamont-Doherty Earth Observatory of Columbia University

These newly documented earthquakes are occurring in glaciated areas of Alaska, Antarctica and Greenland and are caused by the dumping of giant icebergs–equal in size to, say, 400,000 Olympic swimming pools–into the sea. They produce seismic signals equivalent to those found in magnitude 5 earthquakes, which can be felt thousands of kilometers away. And there are many more of them today than there were just a couple of decades ago: six to eight times more than in the early 1990s have been recorded at outlet glaciers along the coast of Greenland.

This sudden surge in glacier earthquakes is expected to set off a series of events that will result in faster sea level rise over the coming century than had previously been estimated, according to research conducted there by Dr. Meredith Nettles, Associate Professor of Earth and Environmental Sciences at Columbia University, and some of her colleagues, as a part of Project SERMI. In 2013, the Intergovernmental Panel on Climate Change (IPCC) revised estimates for the next century dramatically upward (from 11-17 inches by 2100 to 10-39 inches) when taking Dr. Nettles and her colleagues’ earthquake research into account for the first time. This upward revision reflects the fact that the earthquakes change the internal dynamics of the glaciers, causing them to flow more rapidly, and to shed more ice into the ocean.

Monitoring station on Helheim glacier. © SERMI
Monitoring station on Helheim glacier. © SERMI

Nettles gave a talk on glacier earthquakes last November at the American Museum of Natural History. In the summer of 2006, she and 11 other scientists from six institutions in the U.S., Denmark and Spain traveled to a small town in East Greenland to take seismic, GPS and time-lapse photography measurements of the Helheim Glacier. They wanted to examine the location, dynamics and frequency of glacier earthquakes and to develop a method for using seismic data to map changes in the ice. They also wanted to learn how these earthquakes shape the behavior of outlet glaciers, which cluster around coastlines and deposit ice and meltwater into the oceans.

After setting up camp in town, the scientists flew a helicopter out to the glacier, drilled holes 6 feet deep in the ice, and drove 9-foot poles into those holes to anchor their GPS, time-lapse and seismic equipment. From the data they collected, they learned that short-term acceleration of glacier ice flows—up to 25% increases in velocity—coincided with the earthquakes. They also found that the increase in glacier earthquakes corresponded to net retreat of the ice front in Greenland. In particular, the section of the Greenland coast with earthquake-producing glaciers expanded northward. And whereas in the 1990s, a few glaciers were causing earthquakes; by 2005, those glaciers were associated with more frequent earthquakes, and other glaciers began to have seismic activity as well.

Map showing locations of GPS stations (blue and yellow dots). Arrows show average velocities over this time period. Red dots represent locations of rock-based GPS reference sites. Dashed lines show the location of the calving front at the beginning (eastern line) and end (western line) of the network operation period. Inset shows location of Helheim glacier in southeast Greenland (black arrow) and locations of glacial earthquakes (white dots). © Glacial Earthquakes in Greenland and Antarctica, Meredith Nettles and Göran Ekström, Lamont-Doherty Earth Observatory of Columbia University
Map showing locations of GPS stations (blue and yellow dots). Arrows show average velocities over this time period. Red dots represent locations of rock-based GPS reference sites. Dashed lines show the location of the calving front at the beginning (eastern line) and end (western line) of the network operation period. Inset shows location of Helheim glacier in southeast Greenland (black arrow) and locations of glacial earthquakes (white dots).
© Glacial Earthquakes in Greenland and Antarctica, Meredith Nettles and Göran Ekström, Lamont-Doherty Earth Observatory of Columbia University

Future research should focus on ice-ocean interactions that promote or reduce glacier calving, said Nettles. And scientists still need to better understand the specific mechanisms of loss of ice at the calving front and the effects of loss of ice on flow speeds. Nettles’ current research examines the impact of tides on glacier calving. Preliminary analysis of the data suggests that glacier earthquakes are more likely to occur at low tide.

Nettles and her colleagues collected most of their seismic data and GPS observations of the glacial earthquakes through facilities run jointly by IRIS (Incorporated Research Institutions for Seismology) and the USGS (U.S. Geological Survey). Thanks to grants from the USGS and the National Science Foundation, that data is open sourced and available to the public.

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