Posts tagged climate change
CU Boulder study: Alaska’s iconic Columbia Glacier expected to stop retreating in 2020
Nov 26th
The wild and dramatic cascade of ice into the ocean from Alaska’s Columbia Glacier, an iconic glacier featured in the documentary “Chasing Ice” and one of the fastest moving glaciers in the world, will cease around 2020, according to a study by the University of Colorado Boulder.
A computer model predicts the retreat of the Columbia Glacier will stop when the glacier reaches a new stable position — roughly 15 miles upstream from the stable position it occupied prior to the 1980s. The team, headed by lead author William Colgan of the CU-Boulder headquartered Cooperative Institute for Research in Environmental Sciences, published its results today in The Cryosphere, an open access publication of the European Geophysical Union.
The Columbia Glacier is a large (425 square miles), multi-branched glacier in south-central Alaska that flows mostly south out of the Chugach Mountains to its tidewater terminus in Prince William Sound.
Warming air temperatures have triggered an increase in the Columbia Glacier’s rate of iceberg calving, whereby large pieces of ice detach from the glacier and float into the ocean, according to Colgan. “Presently, the Columbia Glacier is calving about 2 cubic miles of icebergs into the ocean each year — that is over five times more freshwater than the entire state of Alaska uses annually,” he said. “It is astounding to watch.”
The imminent finish of the retreat, or recession of the front of the glacier, has surprised scientists and highlights the difficulties of trying to estimate future rates of sea level rise, Colgan said. “Many people are comfortable thinking of the glacier contribution to sea level rise as this nice predictable curve into the future, where every year there is a little more sea level rise, and we can model it out for 100 or 200 years,” Colgan said.
The team’s findings demonstrate otherwise, however. A single glacier’s contribution to sea level rise can “turn on” and “turn off” quite rapidly, over a couple of years, with the precise timing of the life cycle being difficult to forecast, he said. Presently, the majority of sea level rise comes from the global population of glaciers. Many of these glaciers are just starting to retreat, and some will soon cease to retreat.
“The variable nature and speed of the life cycle among glaciers highlights difficulties in trying to accurately predict the amount of sea level rise that will occur in the decades to come,” Colgan said.
The Columbia Glacier was first documented in 1794 when it appeared to be stable with a length of 41 miles. During the 1980s it began a rapid retreat and by 1995 it was only about 36 miles long. By late 2000 it was about 34 miles long.
The loss of a massive area of the Columbia Glacier’s tongue has generated a tremendous number of icebergs since the 1980s. After the Exxon Valdez ran aground while avoiding a Columbia Glacier iceberg in 1989, significant resources were invested to understand its iceberg production. As a result, Columbia Glacier became one of the most well-documented tidewater glaciers in the world, providing a bank of observational data for scientists trying to understand how a tidewater glacier reacts to a warming climate.
Motivated by the compelling imagery of the Columbia Glacier’s retreat documented in the Extreme Ice Survey — James Balog’s collection of time-lapse photography of disappearing glaciers around the world — Colgan became curious as to how long the glacier would continue to retreat. To answer this question, the team of researchers created a flexible model of the Columbia Glacier to reproduce different criteria such as ice thickness and terminus extent.
The scientists then compared thousands of outputs from the computer model under different assumptions with the wealth of data that exists for the Columbia Glacier.
The batch of outputs that most accurately reproduced the well-documented history of retreat was run into the future to predict the changes the Columbia Glacier will most likely experience until the year 2100. The researchers found that around 2020 the terminus of the glacier will retreat into water that is sufficiently shallow to provide a stable position through 2100 by slowing the rate of iceberg production.
The speediness of the glacier’s retreat is due to the unique nature of tidewater glaciers, Colgan said. When warming temperatures melt the surface of a land glacier, the land glacier only loses its mass by run-off. But in tidewater glaciers, the changes in ice thickness resulting from surface melt can create striking changes in ice flow, triggering an additional dynamic process for retreat.
The dynamic response of the Columbia Glacier to the surface melt will continue until the glacier reaches its new stable position in 2020, at roughly 26 miles long. “Once the dynamic trigger had been pulled, it probably wouldn’t have mattered too much what happened to the surface melt — it was just going to continue retreating through the bedrock depression upstream of the pre-1980s terminus,” Colgan said.
Colgan next plans to attempt to use similar models to predict when the Greenland glaciers — currently the major contributors to sea level rise — will “turn off” and complete their retreats.
The future for the Columbia Glacier, however, looks bleak. “I think the hope was that once we saw climate change happening, we could act to prevent some irreversible consequences,” Colgan said, “but now we are only about eight years out from this retreat finishing — it is really sad. There is virtually no chance of the Columbia Glacier recovering its pre-retreat dimensions on human time-scales.”
The study was funded by NASA, and co-authors on the paper include W. Tad Pfeffer of CU-Boulder’s Institute of Arctic and Alpine Research, Harihar Rajaram of the CU-Boulder Department of Civil, Environmental, and Architectural Engineering, Waleed Abdalati of the National Aeronautic and Space Administration in Washington, D.C., and Balog of the Extreme Ice Survey in Boulder, Colo.
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CU-NOAA study shows summer climate change, mostly warming
Nov 15th
“It is the first time that we show on a local scale that there are significant changes in summer temperatures,” said lead author CIRES scientist Irina Mahlstein. “This result shows us that we are experiencing a new summer climate regime in some regions.”
The technique, which reveals location-by-location temperature changes rather than global averages, could yield valuable insights into changes in ecosystems on a regional scale. Because the methodology relies on detecting temperatures outside the expected norm, it is more relevant to understand changes to the animal and plant life of a particular region, which scientists would expect to show sensitivity to changes that lie outside of normal variability.
“If the summers are actually significantly different from the way that they used to be, it could affect ecosystems,” said Mahlstein, who works in the Chemical Sciences Division of the National Oceanic and Atmospheric Administration’s Earth System Research Laboratory.
To identify potential temperature changes, the team used climate observations recorded from 1920 to 2010 from around the globe. The scientists termed the 30-year interval from 1920 to 1949 the “base period,” and then compared the base period to other 30-year test intervals starting every 10 years since 1930.
The comparison used statistics to assess whether the test interval differed from the base period beyond what would be expected due to yearly temperature variability for that geographical area.
Their analysis found that some changes began to appear as early as the 1960s, and the observed changes were more prevalent in tropical areas. In these regions, temperatures varied little throughout the years, so the scientists could more easily detect any changes that did occur, Mahlstein said.
The scientists found significant summer temperature changes in 40 percent of tropical areas and 20 percent of higher-latitude areas. In the majority of cases, the researchers observed warming summer temperatures, but in some cases they observed cooling summer temperatures.
“This study has applied a new approach to the question, ‘Has the temperature changed in local areas?’ ” Mahlstein said. The study is in press in the journal Geophysical Research Letters, a publication of the American Geophysical Union.
The study’s findings are consistent with other approaches used to answer the same question, such as modeling and analysis of trends, Mahlstein said. But this technique uses only observed data to come to the same result. “Looking at the graphs of our results, you can visibly see how things are changing,” she said.
In particular the scientists were able to look at the earlier time periods, note the temperature extremes, and observe that those values became more frequent in the later time periods. “You see how the extreme events of the past have become a normal event,” Mahlstein said.
The scientists used 90 years of data for their study, a little more than the average lifespan of a human being. So if inhabitants of those areas believe that summers have changed since they were younger, they can be confident it is not a figment of their imagination.
“We can actually say that these changes have happened in the lifetime of a person,” Mahlstein said.
Co-authors on the study were Gabriele Hegerl from the University of Edinburgh in Scotland and Susan Solomon from Massachusetts Institute of Technology.
CIRES is a joint institute of CU-Boulder and NOAA.
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CU project: Degraded military lands to get ecological boost
Nov 15th
Headed up by CU-Boulder Assistant Professor Nichole Barger, the research team is focused on developing methods to restore biological soil crusts — microbial communities primarily concentrated on soil surfaces critical to decreasing erosion and increasing water retention and soil fertility. Such biological soil crusts, known as “biocrusts,” can cover up to 70 percent of the ground in some arid ecosystems and are dominated by cyanobacteria, lichens, mosses, fungi and bacteria, she said.
The project is aimed at restoring fragile habitats in desert areas that have been affected by the movement of U.S. military vehicles, including tanks, as well as high foot traffic, said Barger, a faculty member in CU-Boulder’s ecology and environmental biology department. The team has two U.S. Department of Defense study sites — Fort Bliss, which straddles southern Texas and New Mexico and is located in a hot desert environment, and the Dugway Proving Ground in northwest Utah, seated in a cool desert environment.
“Biocrusts often are associated with increased soil nutrients and water retention, but their most important task is to stabilize soil surfaces against wind and water erosion,” Barger said. “While most biocrusts are relatively resilient to wind and water erosion, they are highly susceptible to compressional forces like those generated by foot and vehicle traffic associated with ground-based military activities.”
At military installations like Fort Bliss, the Dugway Proving Ground and in the California/Arizona Maneuver Area in the Mojave Desert used by Patton’s troops, scars of past military activity still are evident, said Barger. “You can go to these places and see that the biocrusts in the old tank tracks, for example, are completely different than nearby biocrusts undisturbed by military activity.”
The project is being funded by a five-year, $2.3 million grant from the Strategic Environmental Research and Development Program, the U.S. Department of Defense environmental science and technology program that partners with the U.S. Department of Energy and the Environmental Protection Agency. The research team also includes Jayne Belnap, Michael Duniway and Sasha Reed from the U.S. Geological Survey’s Biological Resources Division in Moab, Utah and Ferran Garcia-Pichel of Arizona State University in Tempe.
The first step of the program will be to grow biocrusts in laboratories at ASU, said Barger. “Our approach will be to expose laboratory biocrusts over time to a physiological ‘boot camp’ that includes increasing stressors like heat, light and dryness,” she said. “By doing that, we believe the biocrusts we eventually transplant into the study areas will have a higher probability of survival.”
The lab-grown biocrust products will be dried, bagged and transported to field test sites at each respective military installation and sprinkled on soil surfaces, said Barger.
Once in the field, the stress-adapted biocrusts developed in the lab nurseries for both hot desert and cool desert environments will be combined with other soil stabilization strategies, she said. The team, for example, will also experiment with adding polyacrylamide — a soil-stabilizing compound shown to increase soil porosity and reduce erosion, compaction, dustiness and water run-off — to the mix.
The researchers will evaluate the effectiveness of such soil “inoculations” and determine the optimum dosage for the test sites. Following the assisted recovery of the local biocrusts at Fort Bliss and the Dugway Proving Ground, the team will begin a series of seeding trials to develop strategies for native plant re-establishment, Barger said.
The last step of the project will involve a series of rainfall simulations and wind tunnel experiments combined with broad-scale soil erosion modeling to evaluate the influence of biocrust and native plant restoration in terms of precipitation and soil erosion.
While DOD military installations cover nearly 30 million acres — 70 percent of which are located in arid regions of the West — Barger said the research also could aid in the effective management of other federal lands. “We think our work on biocrusts also will be of interest to land managers at agencies like the Bureau of Land Management and the U.S. Forest Service,” Barger said.
The adaptation of biocrusts to extreme environments likely will come into play even more as climate change continues to heat and dry the West, she said. “We expect the drought in the Southwest to intensify as a result of climate change, and this project should tell us more about how adaptive these biocrusts are under shifting environmental conditions.”
The research project also has health implications, said Barger, since the disturbance of biocrusts can trigger the release of significant amounts of atmospheric dust, a dominant pollutant in some desert metropolitan areas. “There is a broad societal interest in stabilizing dryland soils in order to protect not only the functioning of local ecosystems but also human populations that reside in surrounding communities.”
“In terms of tackling an important environmental issue, this is by far the most exciting research project that I have been involved in,” said Barger, who has worked in Hawaii, Central America, South America, China and South Africa.
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