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Topic Name: New Greenland Ice Sheet Data Will Impact Climate Change Models and Also Demonstrates Remote Sensing and Digital Imaging Techniques

Category: Environmental engineering

Research persons: Beata Csatho, Ph.D.

Location: University at Buffalo, United States

Details

A comprehensive new study authored by University at Buffalo scientists and their colleagues for the first time documents in detail the dynamics of parts of Greenland's ice sheet, important data that have long been missing from the ice sheet models on which projections about sea level rise and global warming are based.

The research, published online this month in the Journal of Glaciology, also demonstrates how remote sensing and digital imaging techniques can produce rich datasets without field data in some cases.

Traditionally, ice sheet models are very simplified, according to Beata Csatho, Ph.D., assistant professor of geology in the UB College of Arts and Sciences and lead author of the paper.

"Ice sheet models usually don't include all the complexity of ice dynamics that can happen in nature," said Csatho. "This research will give ice sheet modelers more precise, more detailed data."

The implications of these richer datasets may be dramatic, Csatho said, especially as they impact climate projections and sea-level rise estimates, such as those made by the United Nations Intergovernmental Panel on Climate Change (IPCC).

"If current climate models from the IPCC included data from ice dynamics in Greenland, the sea level rise estimated during this century could be twice as high as what they are currently projecting," she said.

The paper focuses on Jakobshavn Isbrae, Greenland's fastest moving glacier and its largest, measuring four miles wide.

During the past decade, Jakobshavn Isbrae has begun to experience rapid thinning and doubling of the amount of ice it discharges into Disko Bay.

"Although the thinning started as early as the end of the 18th century, the changes we are seeing now are bigger than can be accounted for by normal, annual perturbations in climate," Csatho said.

In order to document the most comprehensive story possible of the behavior of Jakobshavn Isbrae since the Little Ice Age in the late 1800s, Csatho and her colleagues at Ohio State University, the University of Kansas and NASA used a combination of techniques.

These included field mapping, remote sensing, satellite imaging and the application of digital techniques in order to glean "hidden" data from historic aerial photographs as many as 60 years after they were taken.

By themselves, Csatho explained, the two-dimensional pictures were of limited value.

"But now we can digitize them, removing the boundaries between them and turning several pictures into a single 'mosaic' that will produce one data set that can be viewed in three-dimensions," she said.

"By reprocessing old data contained in these old photographs and records, we have been able to construct a long-term record of the behavior of the glacier," said Csatho. "This was the first time that the data from the '40s could be reused in a coherent way."

The data from the historic photos were combined with data from historical records, ground surveys, field mapping and measurements taken from the air to document important signs of change in the glacier's geometry.

Csatho explained that conventional methods of assessing change in glaciers have depended on documenting "iceberg calving," in which large pieces at the front of the glacier break off.

"But we found that you can get significant changes in the ice sheet without seeing a change in front," she said.

Other key findings of the paper are that two different parts of the same glacier may behave quite differently and that a glacier does not necessarily react to climate change as a single, monolithic entity.

"Climate forces are complex," Csatho said. "For example, we found that the northern part of Jakobshavn was still thinning while the climate was colder between the 1960s and the 1990s."

Csatho, who is a geophysicist, added that the research is the result of a strong interdisciplinary team involving experts in glaciology, ice sheet modeling and photogrammetry, the science of making measurements based on photographs.

At UB, research in Csatho's remote sensing laboratory -- http://rsl.geology.buffalo.edu/ -- focuses on a multidisciplinary approach that integrates information across the geosciences.

Note for Greenland Ice Sheet
The Greenland Ice Sheet is a vast body of ice covering 1.71 million km², roughly 80% of the surface of Greenland. It is the second largest ice body in the world, after the Antarctic Ice Sheet. The ice sheet is almost 2,400 kilometers long in a north-south direction, and its greatest width is 1,100 kilometers at a latitude of 77° N, near its northern margin. The mean altitude of the ice is 2,135 meters. The thickness is generally more than 2 km (see picture) and over 3 km at its thickest point. It is not the only ice mass of Greenland - isolated glaciers and small ice caps cover between 76,000 and 100,000 square kilometers around the periphery. Some scientists believe that global warming may be about to push the ice sheet over a threshold where the entire ice sheet will melt in less than a few hundred years. If the entire 2.85 million km³ of ice were to melt, it would lead to a global sea level rise of 7.2 m (23.6 ft.). This would inundate most coastal cities in the world and remove several small island countries from the face of Earth, since island nations such as Tuvalu and Maldives have a maximum altitude below or just above this number.
The Greenland Ice Sheet is also sometimes referred to under the term inland ice, or its Danish equivalent, indlandsis. It is also sometimes referred to as an ice cap. Ice sheet, however, is considered the more correct term as ice cap generally refers to less extensive ice masses.
The ice in the current ice sheet is as old as 110,000 years However, it is generally thought that the Greenland Ice Sheet formed in the late Pliocene or early Pleistocene by coalescence of ice caps and glaciers. It did not develop at all until the late Pliocene, but apparently developed very rapidly with the first continental glaciation.
The massive weight of the ice has depressed the central area of Greenland; the bedrock surface is near sea level over most of the interior of Greenland, but mountains occur around the periphery, confining the sheet along its margins. If the ice were to disappear, Greenland would most probably appear as an archipelago. The ice surface reaches its greatest altitude on two north-south elongated domes, or ridges. The southern dome reaches almost 3,000 metres at latitudes 63° - 65° N; the northern dome reaches about 3,290 metres at about latitude 72° N. The crests of both domes are displaced east of the centre line of Greenland. The unconfined ice sheet does not reach the sea along a broad front anywhere in Greenland, so that no large ice shelves occur. The ice margin just reaches the sea, however, in a region of irregular topography in the area of Melville Bay southeast of Thule. Large outlet glaciers, which are restricted tongues of the ice sheet, move through bordering valleys around the periphery of Greenland to calve off into the ocean, producing the numerous icebergs that sometimes occur in North Atlantic shipping lanes. The best known of these outlet glaciers is the Jakobshavn Isbræ, which, at its terminus, flows at speeds of 20 to 22 metres per day.

Note for Sea-Level Rise
Sea-level rise is an increase in sea level. Multiple complex factors may influence this change.
Sea-level has risen about 130 metres (400 ft) since the peak of the last ice age about 18,000 years ago. Most of the rise occurred before 6,000 years ago. From 3,000 years ago to the start of the 19th century sea level was almost constant, rising at 0.1 to 0.2 mm/yr. Since 1900 the level has risen at 1 to 2 mm/yr; since 1993 satellite altimetry from TOPEX/Poseidon indicates a rate of rise of 3.1 ± 0.7 mm yr–1. Church and White (2006) found a sea-level rise from January 1870 to December 2004 of 195 mm, a 20th century rate of sea-level rise of 1.7 ±0.3 mm per yr and a significant acceleration of sea-level rise of 0.013 ± 0.006 mm per year per yr. If this acceleration remains constant, then the 1990 to 2100 rise would range from 280 to 340 mm,. Sea-level rise can be a product of global warming through two main processes: thermal expansion of sea water and widespread melting of land ice. Global warming is predicted to cause significant rises in sea level over the course of the twenty-first century.
Local mean sea level (LMSL) is defined as the height of the sea with respect to a land benchmark, averaged over a period of time (such as a month or a year) long enough that fluctuations caused by waves and tides are smoothed out. One must adjust perceived changes in LMSL to account for vertical movements of the land, which can be of the same order (mm/yr) as sea level changes. Some land movements occur because of isostatic adjustment of the mantle to the melting of ice sheets at the end of the last ice age. The weight of the ice sheet depresses the underlying land, and when the ice melts away the land slowly rebounds. Atmospheric pressure, ocean currents and local ocean temperature changes also can affect LMSL.
“Eustatic” change (as opposed to local change) results in an alteration to the global sea levels, such as changes in the volume of water in the world oceans or changes in the volume of an ocean basin.

Note for Remote Sensing
In the broadest sense, remote sensing is the small or large-scale acquisition of information of an object or phenomenon, by the use of either recording or real-time sensing device(s) that is not in physical or intimate contact with the object (such as by way of aircraft, spacecraft, satellite, buoy, or ship). In practice, remote sensing is the stand-off collection through the use of a variety of devices for gathering information on a given object or area. Thus, Earth observation or weather satellite collection platforms, ocean and atmospheric observing weather buoy platforms, monitoring of a pregnancy via ultrasound, Magnetic Resonance Imaging (MRI), Positron Emission Tomography (PET), and space probes are all examples of remote sensing. In modern usage, the term generally refers to the use of imaging sensor technologies including but not limited to the use of instruments aboard aircraft and spacecraft, and is distinct from other imaging-related fields such as medical imaging.
There are two kinds of remote sensing. Passive sensors detect natural energy (radiation) that is emitted or reflected by the object or surrounding area being observed. Reflected sunlight is the most common source of radiation measured by passive sensors. Examples of passive remote sensors include film photography, infra-red, charge-coupled devices and radiometers. Active collection, on the other hand, emits energy in order to scan objects and areas whereupon a passive sensor then detects and measures the radiation that is reflected or backscattered from the target. RADAR is an example of active remote sensing where the time delay between emission and return is measured, establishing the location, height, speed and direction of an object.

Note for Digital Imaging
Digital imaging or digital image acquisition is the creation of digital images, typically from a physical object. The term is often assumed to imply or include the processing, compression, storage, printing, and display of such images.
A digital image may be created directly from a physical scene by a camera or similar device. Alternatively, it may be obtained from another image in an analog medium, such as photographs, photographic film, or printed paper, by a scanner or similar device. Many technical images—such as those acquired with tomographic equipment, side-looking radar, or radio telescopes—are actually obtained by complex processing of non-image data. Finally, a digital image can also be computed from a geometric model or mathematical formula (however, in this case the name image synthesis is more appropriate).
Digital image authentication is an emerging issue for the providers and producers of high resolution digital images such as health care organizations, law enforcement agencies and insurance companies. There is currently no method available to analyze a digital image and determine if it has been altered or not. However, there are some technologies on the horizon which are useful in confirming the non-alteration of images whose original producer is known.

The research was funded by the National Science Foundation and NASA.

Csatho's co-authors on the paper are Tony Schenk of the Ohio State University Department of Civil and Environmental Engineering and Geodetic Science; Kees van der Veen of the Center for Remote Sensing of Ice Sheets at the University of Kansas, and William B. Krabill of the National Aeronautics and Space Administration's Cryospheric Sciences Branch.

The University at Buffalo is a premier research-intensive public university, a flagship institution in the State University of New York system that is its largest and most comprehensive campus. UB's more than 28,000 students pursue their academic interests through more than 300 undergraduate, graduate and professional degree programs. Founded in 1846, the University at Buffalo is a member of the Association of American Universities.

In figure 1, Outline Map of Greenland with ice sheet depths. GISP refers to a main site of the Greenland Ice Sheet Project, where a 3 km deep ice core was taken.

In figure 2, This satellite image, colored for emphasis and taken in 2001, shows the ice sheet margins where land (pink areas) has become exposed and lakes were formed (bright blue). The large bluish-green area is the glacier.

In figure 3, Sea level measurements from 23 long tide gauge records in geologically stable environments show a rise of around 20 centimeters per century (2 mm/year).

In figure 4, This 1946 picture shows how the four-mile-wide Jakobshavn Isbrae, the white region in the middle, is flowing from the ice (top) through Greenland's rocky coast.

In figure 5, Research conducted by a UB geologist on the Greenland ice sheet shows the trimline (broken brown line) that marks the maximum extent of the ice sheet at the end of the 18th century and the subsequent retreat of the glacier and land exposed since 1944.