The Wikipedia page for Taku Glacier needs updating.
Taku Glacier, the deepest and thickest alpine temperate glacier in the world, is no longer the only major glacier advancing in the Juneau Icefield––it is finally receding. Taku, which measures 4,845 feet (1,477 m) and 36 miles (58 km) long, was long heralded as a symbolic holdout to the melt that has most glaciers in retreat.
Mauri Pelto is a professor of environmental science at Nichols College and director of the North Cascades Glacier Climate Project. “This is a big deal for me because I had this one glacier I could hold on to,” Pelto told NASA. “But not anymore. This makes the score climate change: 250 and alpine glaciers: 0.”
The determination that Taku has succumbed to the warming climate was made after completing annual end-of-summer snowline measurements. Surface melt is responsible for the glacier’s turnaround, according to Pelto. The Juneau Icefield Research Program has been watching and reporting Taku’s yearly mass balance to the World Glacier Monitoring Service since 1946.
The glacier had been expected to continue advancing through the rest of the century. “To be able to have the transition take place so fast indicates that climate is overriding the natural cycle of advance and retreat that the glacier would normally be going through,” Pelto said.
This post was originally published on the American Geophysical Union blog on September 24, 2018.
Brady Glacier is a large Alaskan tidewater glacier in the Glacier Bay region that is beginning a period of substantial retreat (Pelto et al. 2013). Pelto et al. (2013) noted that the end of season observed transient snowline averaged 725 m from 2003-2011, well above the 600 m that represents the equilibrium snowline elevation for the glacier to sustain its current size. In 2015, 2016 and 2018, the snowline has been at 900-1000 m. This is leading to thinning across what was much of the accumulation zone. Here we examine Landsat images from 1986 to 2018 to identify signs of this thinning.
In 1986, Point A and B have insignificant rock exposure, while C has a limited single rock nunatak. By 2000, there is bedrock exposed west of Point A and B, with two small nunataks near C. By 2015, there is a 2 km-long bedrock ridge at Point A and a ~1 km-long bedrock ridge at Point B. The snowline in 2015 is just above Point B and C at 900 m. In 2016, on 1 Oct. 2016, after the end of the typical melt season, the snowline is at 900 m. In 2018, the snowline on Sept. 21 is at 1000 m. At Point A the bedrock ridge is now 2300 m long and up to 300 m wide. At Point A, the ridge is 1100 m long. At Point C, a third nunatak has emerged, and the series of nunataks will soon merge into a single ridge.
The persistent high snowlines indicate the consistent accumulation zone is now above 900 m, below this point thinning will continue. The mean elevation of the glacier is at 720 m, and thinning is significant below 1000 m from 1995-2011(Johnson et al, 2013). That is far less than 50 percent the glacier is retaining snowpack, and widespread thinning will drive further retreat of the distributary glacier termini in expanding lakes, noted by Pelto et al. (2013) and a 2016 blog post. Brady Glacier abuts the adjacent Lampugh Glacier that has and will be impacted by a large landslide.
Trick Lakes: In 1986, North and South Trick Lake are proglacial lakes in contact with the glacier. By 2016, the two lakes are no longer in contact with the glacier, water levels have fallen and a third lake, East Trick Lake, has formed. The more recently developed East Trick Lake is the current proglacial Trick Lake, a large glacier river exits this lake and parallels the glacier to the main Brady Glacier terminus, going beneath the glacier for only several hundred meters.
North Deception Lake: Had a limited area in 1986 with no location more than 500 m long. By 2016, retreat has expanded the lake to a length over 2 km. The width of the glacier margin at North Deception Lake will not change in the short term, but the valley widens 2 km back from the current calving front, thus the lake may grow considerably in the future.
South Dixon Lake: This new lake does not have an official name. It did not exist in 1986, 2004, 2007 or 2010. It is nearly circular today and 400 m in diameter.
Dixon Lake: It is likely that retreat toward the main valley of Brady Glacier will lead to increased water depths at Dixon Lake, observations of the depth of this lake do not exist. Retreat from 1986 to 2016 has been 600 m.
Bearhole Lake: Is expanding up valley with glacier retreat, and there are no significant changes in the width of the valley that would suggest a significant increase in calving width could occur in the near future. Currently, the lake is 75 m deep at the calving front, and there has been a 1400 m retreat since 1986 (Capps et. al. 2013).
Spur Lake: It is likely that retreat toward the main valley of Brady Glacier will lead to increased water depths at Spur Lake. The depth has fallen as the surface level fell from 1986-2016 as the margin retreated 600 m, leaving a trimline evident in the 2016 imagery.
Oscar Lake: Has experienced rapid growth with the collapse of the terminus tongue. Depth measurements indicate much of the calving front, which has increased by an order of magnitude since 1986, is over 100 m. The tongue, as seen in a 2014 Google Earth image, will continue to collapse, and water depth should increase as well. The central narrow tongue has retreated less than 200 m since 1986, but the majority of the glacier front has retreated more than 1 km since 1986.
Abyss Lake: Continued retreat will lead to calving width expansion. The retreat from 1986 to 2016 has been 400 m. The water depth has been above 150 m at the calving front for sometime and should remain high.
The Trump administration is assessing a 545-page draft report about the causes and impacts of global warming, including the imminent threat of glacial retreat. This draft report known as the Climate Science Special Report is part of the fourth National Climate Assessment, and it is undergoing a final interagency review by the administration, the Environmental Protection Agency (EPA), and 12 other agencies. The New York Times published the draft report on August 7th, which brought a good deal of attention to the document, even though the information had been available at the Internet Archive, a nonprofit internet digital library, since January.
On August 20th, the Trump administration took initial steps to weaken the effectiveness of the draft report bydisbanding the federal advisory panel for the National Climate Assessment, the group that guides the report and helps policymakers and private-sector officials integrate climate analysis into long-term planning, raising questions about the future of the report. The charter for the advisory committee will expire on Sunday, August 27th, and the panel will not be renewed.
The report was written by a team of more than 300 experts from 13 federal agencies. The National Climate Assessment is one of the most rigorously sourced and vetted documents produced by the federal government, based on “peer reviewed journal articles, technical reports by federal agencies, scientific assessments, etc” and produced every four years since 1990. The latest assessment, which ultimately could be rejected by the Trump administration, concludes that the average annual temperature will continue to rise throughout the century, with global temperatures increasing between 0.5 and 1.3 degrees Fahrenheit over the next two decades. This could result in longer heat waves, disappearing snow cover, shrinking sea ice, and melting glaciers.
Mark Carey, a professor of history and environmental studies at the University of Oregon, told GlacierHub that shrinking glaciers actually have notable impacts. “For one, they help regulate water flow in glacier-fed rivers, providing meltwater for downstream water use in dry summer months when farmers and hydroelectric power stations most need the water,” he said. “Glacier retreat can also unleash outburst floods and avalanches from the unstable glaciers.”
According to the assessment, the annually averaged ice mass from 37 global reference glaciers “has decreased every year since 1984, a decline expected to continue even if climate were to stabilize.” The findings stirred public interest because they refute statements from the Trump administration about the causes and effects of climate change. The Trump administration, including his cabinet members, have taken a different approach to combatting global warming, repealing environmental regulations and defunding climate research. Earlier this year, Trump pulled the United States out of the Paris climate accord and rolled back policies that former President Barack Obama put in place, such as the Clean Power Plan, which limits greenhouse gas emissions from U.S. power plants.
The Trump administration also worked hard to save the coal industry and promised to increase oil and gas production by drilling in protected areas of the Arctic and Atlantic Oceans, which will increase emissions. Additionally, Trump has appointed members to his cabinet who openly deny anthropogenic climate change. Agency scientists have found that discussing climate change with EPA leadership has become taboo. The Interior and Agriculture departments have also banned climate change talk and cancelled meetings with climate change experts. The report is one of the administration’s biggest tests to date in regard to the their public opinion on climate change.
Scott Pruitt, the head of the EPA, recently told CNBC, “I think that measuring with precision human activity on the climate is something very challenging to do and there’s tremendous disagreement about the degree of impact, so no, I would not agree that it’s a primary contributor to the global warming that we see.” Since Pruitt’s arrival at the EPA, the agency has moved away from its historic practice of publicly posting data collections of emissions from oil and gas companies. To date, the EPA has also taken down more than 1,900 agency web pages that contain climate change information. It is also attempting to undo a water protection rule in order to dismantle previous regulations.
If the Trump administration rejects the information in the latest assessment, the move would be another step away from the global consensus, which recognizes melting glaciers, disappearing snow cover, and the reduction in the volume of mountain glaciers and continental ice sheets. By rejecting the report, Trump’s administration would directly contradict scientific conclusion that “many lines of evidence demonstrate that human activities, especially emissions of greenhouse (heat-trapping) gases, are primarily responsible for recent observed climate change.” Specifically, the report concluded that the planet has rapidly warmed over the last 150 years, finding it “extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century.”
In an interview with GlacierHub, Mauri Pelto, a professor of environmental science at Nichols College in Massachusetts and director of the North Cascades Glacier Climate Project, stated that the report’s disapproval would put in disarray the carefully constructed practices and approach used to build the report, but it would also further galvanize the scientific community to bring more science directly into the public eye. “A report from a different configuration of science organizations would certainly emerge,” Pelto said. “In the short run it will be a challenge to the community, but in the long run it will strengthen this community. Less dependence on the government for both funding and sanctioning is the challenge and the opportunity.”
Shrinking glaciers are oft-cited examples of the effects of anthropogenic climate change, providing dramatic imagery in different parts of the world. However, this has mostly been based on global aggregates of glacier extent. Differing opinions also exist about the best way to measure glacial change all over the world. A recent study by Roe et al., published in Nature Geoscience, confirms that climate change has contributed to the shortening of numerous glaciers around the world, but the study is not immune to controversy surroundings the methods used.
Using a combination of meteorological data and observations of glacier length, Roe et al. studied the influence of climate on 37 glaciers between 1880 and 2010. The glaciers were selected based on the continuity of length observations and the need for a wide geographical distribution.
Glacier mass-balance records are a more direct measure of the effect of climate than glacier length as they measure the difference between the accumulation and ablation (sublimation or melting) of glacier ice. However, most mass-balance records do not extend for more than two decades, contributing to the previous lack of confirmation of the effect of climate change on individual glaciers around the world.
The use of observations of glacier length helped to overcome this obstacle, but challenges were still encountered in obtaining long, continuous data sets, particularly for regions such as Asia and South America. In conversation with GlacierHub, Roe shared that many factors can affect the availability of continuous data sets. “For example, the collapse of the Soviet Union led to many glacier observation programs being abandoned,” he stated.
An additional challenge arose from the variation in conditions experienced by each glacier. “Every glacier is a unique product of its local climate and landscape,” Roe shared, citing the example of maritime glaciers, which typically experience a large degree of wintertime accumulation variability. “This can mask the signal of a warming that, so far, has mainly impacted the summertime mass balance,” he added.
Nevertheless, Roe et al. found that there was at least a 99% chance that a change in climate was needed to account for the retreat of 21 of the glaciers studied. “Even for the least statistically significant (Rabots Glacier in Sweden), there was still an 89% chance that its retreat required a climate change,” Roe said.
As glaciers tend to have decadal responses to changes in climate, their retreat since 1880 is likely to be a result of twentieth-century temperature trends. They also act as amplifiers of local climate trends, providing strong signal-to-noise ratios that serve as strong evidence for the effects of anthropogenic climate change. For example, one of the glaciers included in the study, Hintereisferner in the Austrian Alps, retreated 2,800m since 1880, with a standard deviation (a measure of the deviation of values from the mean) of 130m. This value is small compared to the amount of retreat, providing a strong signal of change.
“We hope that these results will lead to a stronger scientific consensus about the cause of glacier retreat. The last round of the Intergovernmental Panel on Climate Change was quite timid, concluding only that it was ‘likely’ that a ‘substantial’ part of glacier retreat was due to human-caused climate change,” Roe added. IPCC nomenclature would make it “very likely” (≥90%) that all but one of the glaciers in this study have retreated because of climate change, allowing for stronger conclusions to be drawn.
Excitement about the results of this study was shared by Joerg Schaefer, professor at the Lamont-Doherty Earth Observatory: “Under Roe’s lead, the really smart glacier people find ways to explain this strange observation that glaciers are highly individual beasts if you look at short time scales (years and decades), but behave like a flock of well-behaved sheep when you look at longer (centennial and millennial time-scales),” Schaefer said in an interview with GlacierHub. “This will help us a lot down the road to better predict rates of glacier change for the next century.”
In contrast, Mauri Pelto, professor of environmental science at Nichols College who has been involved in the North Cascade Glacier Climate Project for 34 of years, expressed that the paper was interesting but not the first confirmation of glaciers being impacted by anthropogenic climate change. “This does not mean it is not worth writing about,” said Pelto, “but it needs to be placed in the context of the other key studies that were both earlier, and, I believe, stronger.”
For example, the authors looked at fewer glaciers than Oerlemans et al. (2005) while modelling each in more detail. Pelto notes that they also used far less data than Zemp et al. (2015) in making an even more compelling statement on the status of glaciers. Finally, the authors are not the first to conduct an attribution study: note Marzeion et al. (2014). While their statistical method is quite robust, their modelling approach that generates data does not have an impressive verification record, according to Pelto.
“Other recent studies better represent the certainty of glacier change being driven by climate,” Pelto concluded.
These opinions indicate that glacier retreat continues to attract attention and stimulate active debate, pointing to the importance of glaciers and climate change. The approach used in this study relies on glacier length, a less precise measure than mass-balance. However, its value lies in the ability to consider long meteorological and glacier length records for a number of glaciers, contributing to an important and growing body of knowledge about the effects of anthropogenic climate change on glaciers all over the world.