Disappearing Glaciers in Glacier National Park

What Remains of Agassiz Glacier in GNP

Sometimes well-meaning people shoot themselves in the foot. Somebody at Glacier National Park put up signs indicating that all the glaciers in Glacier National Park would be "gone by the year 2020."

Sign at GNP

The strange thing about this is that the statement wasn't accurate even when the signs were made. The  reference to "computer models" refers to a paper published in 2003[1] that made predictions under two scenarios regarding a subset of the glaciers in the Blackfoot-Jackson Basin of GNP, with one scenario "based on carbon dioxide–induced global warming and the other on a linear temperature extrapolation." 

The Area for the Modeling Study

To evaluate how well this model has performed, it's important here to understand how these two scenarios were defined. I'll quote the paper's definition of each.

1. Scenario 1: "The carbon dioxide–doubling scenario, is based on the US Environmental Protection Agency’s prediction of a doubling of atmospheric carbon dioxide by year 2030 (Smith and Tirpak 1989) with a concurrent global temperature response of 2.5ºC by year 2050. This is IPCC’s “best estimate of climate sensitivity” for a doubling of carbon dioxide. For the period 1990–2100, we incorporate scientists’ prediction (Houghton et al. 1992) of a total temperature increase of 3.3º C and 5% to 10% increases in winter precipitation for middle- and high-latitude continents." 
2. Scenario 2: "The linear temperature–extrapolation scenario, assumes a cyclical climate not linked to human-caused increases in atmospheric concentrations of carbon dioxide. Future temperatures for 1990–2100 are based on linear extrapolation of the global warming trend from 1850 to 1980, portraying the gradual emergence from the Little Ice Age."

So clearly Scenario 1 is based on a rate of increase of CO2 that we are not experiencing. Today in 2025 (just 5 years from 2030), CO2 is just over 50% higher than preindustrial levels, and global warming is currently at 1.3ºC above preindustrial levels. So even though this scenario is based on a good assessment of climate sensitivity, it's based on a scenario that we didn't follow. So we should not expect that all the glaciers in the Blackfoot-Jackson Basin of GNP would "disappear by 2030" as predicted by Scenario 1.

The Model Predicted Glacier Area Reduced to 0 km^2 by 2030
if CO2 doubles by 2030

Scenario 2 was based on a linear increase temperatures following the trend from 1850 to 1980. Since scenario 2 assumes warming at a slower rate than is currently observed, we also should not expect the glaciers in GNP to last as long as predicted under this scenario. In this model, over half the glacial area in 1990 is still present in 2100.

The Model Predicted Too Little Loss of Glacial Area in Scenario 2.

So the best way to understand the model's results is that it puts an upper and lower bound on when we'd expect glaciers to disappear from GNP. We should not expect these glaciers to be gone by 2030, but we also can't be confident that they will still be around in 2100. So why were signs made that glaciers would be gone by 2020? Good question. According to Yale Climate Connections, it's because "field observations showed glacier melt to be years ahead of the projections, causing scientists in 2010 to revise their 'end date' to 2020." The National Park Service has this explanation:

In 2003, researchers published an academic paper about two of the park's glaciers in the Journal of BioScience. They used a geospatial computer model to predict the advance or retreat of Blackfoot Glacier and Jackson Glacier for each decade from 1990 to 2100 based on melting rates from historical data. Since Blackfoot and Jackson are relatively large glaciers, some experts hypothesized that if those two glaciers were completely melted then all the other glaciers in the park likely would be as well. A few years later the researchers looked again at how fast Blackfoot and Jackson were shrinking and found that they seemed to be melting faster than they first predicted. Informally, the researchers moved their 2030 date up to 2020. These predictive dates spread widely and were featured on various exhibits around the park. As 2020 approached, and scientific understanding of glacial melt advanced, the 2020 and 2030 prediction dates were removed. Since then, the exhibits have been updated to reflect more recent research.

In other words, field observations showed glacial area in two of the largest glaciers taking a nose dive, and this lead to concerns that the model may have under-predicted the rate of glacial area loss. They made an informal internal assessment which ended up being written on signs in the park as "computer models indicate the glaciers will all be gone by the year 2020." Somebody made a mistake, both in not checking what the model results actually said and also not understanding that natural variability plays a significant role short-term.

Following the publication of the 2003 model, a 2017 study[2] found that higher elevation glaciers may be more resistant to melting than expected in 2003. These higher elevation glaciers are more shaded and receive more deposition from avalanches and windblown snow; the higher accumulation rates would make them more resistant to warming. It's now looking more like the lower, thinner portions of glaciers may melt extremely rapidly while the higher altitude portions of glaciers may hold on a little longer than expected in 2003. But the evidence clearly shows these glaciers are retreating rapidly, and when they disappear depends on the emission scenario we actually follow. So the signs at GNP have been revised.

New Signs at GNP

Periodically the USGS oversees an inventory of the glacial area in GNP. This was done in 1966, 1998, 2005, and 2015, and these results can be compared to 1850. It looks like they may have standardized these reports every decade, so perhaps a new survey will be conducted this year. The glacial area has dropped significantly with each survey:

Year	Area (km^2)	Percent of 1850
1850	42.99	100%
1966	20.76	48.29%
1998	15.67	36.45%
2005	14.86	34.56%
2015	13.63	31.71%

Since these data points are unequally spaced, it can give the impression that melting is slowing down, but here's how the data looks when plotted by year. Note these numbers are for the entire park, not for the Blackfoot-Jackson Basin subset of glaciers in the tables shown above.

Clearly there's a downward trend, and the glaciers at GNP are on a path towards extinction. Since there's a minimum amount of ice a glacier must have to fit the definition of a glacier (about 0.1 km^2 or 25 acres), we do not have to get completely to 0 before it would be fair to say all the glaciers are gone from GNP. I'm not an expert on the glaciology of GNP, but given what I've read in the 2017 assessment it seems plausible me that if high elevation glaciers are more resistant to melting than the 2003 model suggests, we may be on track for something like this, which uses a polynomial fit to the data, which can't be predictive long term (the curve is parabola shaped). This is just a guess based on 5 data points, so take it with a grain of salt.

It will be interesting to see what comes out of the next survey, which I'm hoping is being done this year. But the lesson learned here is that sign makers at GNP made a big mistake, and that mistake fed into the conspiracy theories of bloggers and political propagandists. But the data is absolutely clear here that the glaciers at GNP are retreating rapidly, and while the data doesn't support even a 2030 date for the extinction of glaciers in the park, no computer model predicted that they would be gone by 2020 or 2030 given the scenario we have actually followed. 

Kinnerly Peak from Kintla Lake

It's also absolutely clear that precious few glaciers remain in the park. I did a two-week long backpacking trip through the park in 2022 and saw what what remains of them (here's some of my favorite photos from the trip). If you go to GNP to see beautiful scenery and wildlife, you will not be disappointed. This may be my favorite park I've ever visited for its amazing beauty. But if you go to see glaciers, you'll be sorely disappointed.

References:

[1] Myrna H. P. Hall, Daniel B. Fagre, Modeled Climate-Induced Glacier Change in Glacier National Park, 1850–2100, BioScience, Volume 53, Issue 2, February 2003, Pages 131–140, https://doi.org/10.1641/0006-3568(2003)053[0131:MCIGCI]2.0.CO;2

[2] Fagre, D.B., McKeon, L.A., Dick, K.A., and Fountain, A.G., 2017, Glacier margin time series (1966, 1998, 2005, 2015) of the named glaciers of Glacier National Park, MT, USA: U.S. Geological Survey data release, https://doi.org/10.5066/F7P26WB1.

[3] USGS. Northern Rocky Mountain Science Center. Table of Area of the Named Glaciers of National Park and Forest. https://www.usgs.gov/media/files/table-area-named-glaciers-national-park-and-forest

[4] Fountain, A. G., Glenn, B., and Mcneil, C.: Inventory of glaciers and perennial snowfields of the conterminous USA, Earth Syst. Sci. Data, 15, 4077–4104, https://doi.org/10.5194/essd-15-4077-2023, 2023. https://essd.copernicus.org/articles/15/4077/2023/essd-15-4077-2023.pdf