January 3, 2007

The Park Formerly Known as Glacier

Glacier National Park just seems to come up repeatedly in the debate about global warming. This poster child of the greenies is sacred ground, for it provides an opportunity to show the kids where the glaciers were when you were a kid, see where the glaciers terminate today, and of course blame global warming and further blame the Bush Administration for not signing the Kyoto Protocol. Many documentaries on the greenhouse effect have been drawn to the Park, and if you Google “Glacier National Park and Global Warming,” you will be directed to approximately 159,000 sites.

A very interesting paper on Glacier National Park appears in a recent issue of Earth Interactions by scientists at Montana State University and the U.S. Geological Survey. Pederson et al. begin their article noting that “Evidence from an increasingly rich paleoproxy record demonstrates that over the last millennium decadal to multidecadal precipitation anomalies have been a substantial, if not defining, component of western North America’s climates. As in the twentieth century, the last 1000 yr has experienced sporadic episodes of both persistent (>10 yr) droughts and wet regimes, though the magnitude and duration of many paleodroughts surpass those captured by the instrumental record.” The notion that droughts in the past were far worse than any recent drought brought our attention to the article, but there is far more to the story than just past droughts.

The team of scientists is well known for their work in reconstructing climate from tree rings, and in discussing the trees around Glacier National Park, they note “As a result, long-duration, moisture-sensitive tree-ring records provide the primary means for examining decadal to multidecadal variability in the hydroclimatic system. In the Rocky Mountains, ring widths from climatically sensitive trees are especially suited to this purpose because they provide records of moisture variability that encompass several centuries or even millennia.”

So off they went to the Park and surrounding areas, and they sampled Douglas fir and Limber pine trees from mid-elevation (1600–2040 m) sites in the Livingston, Lewis, and southeastern Teton mountain ranges. They state that “All samples were taken from open-grown stands located on well-drained, south-facing slopes with sparse understory vegetation without signs of recent disturbance.” They exhaustively cored 243 different trees and brought back to the lab a total of 385 cores from trees ranging in age from 341 to 885 years old. Using historical climate data, they prepared response functions to determine how local climate variations impact the width of tree rings, and from those functions, along with a lot of other statistical wizardry, they developed a reconstruction of summer (June-August) soil moisture variability.

Figure 1 below is amazing. The top of the two plots shows the observed and reconstructed mean summer soil moisture deficit over the past century, and during a century of atmospheric greenhouse gas buildup, we at World Climate Report cannot see any trend in the data or any increase or decrease in variability in the time series. Over the period of instrumental records, the great drought seems to have occurred from 1917 to 1941, with no significant droughts thereafter. However, the lower plot shows us the reconstructed drought levels back to 1540, and once again, we wonder why we are not seeing more drought or more variability in the recent 50 years? The 1917-1941 drought was a big one, but they note “In terms of intensity (magnitude/duration), the 1917–41 drought was surpassed only by the drought of 1601–09.”

Figure 1. The summer drought reconstruction for Glacier National Park. (a) Comparison of the observed and reconstructed mean summer deficit records for the 1900–2000 calibration period. (b) Mean centered reconstructed mean summer deficit (blue line) and smoothed values (thick red line) spanning 1540–2000. (c) Decadal-scale drought regimes exhibiting the significant step changes in the mean (from Pederson et al., 2006).

A second figure in the article (our Figure 2) caught our eye as well showing the drought reconstructions along a transect from New Mexico to Alberta. We have examined all six reconstructions, and we cannot find anything unusual going on in terms of drought frequency, duration, or variability. Every reconstruction shows that droughts in the past were every bit as severe as anything seen over the most recent 100 years. In many cases, the trend of the past 100 years is toward a moister regime, not the drier regime promised by the global warming advocates.

Figure 2. Location of tree-ring-based precipitation and drought reconstructions used in comparison of moisture conditions along a north–south Rocky Mountain transect (from Pederson et al., 2006).

A third figure from the article (our Figure 3) is our favorite, for as seen below, it presents the drought record, a snowpack time series, total hectares burned in the Park, and best of all, the Sperry Glacier retreat timeline. Note that the Sperry Glacier had an area of 3.31 km2 in 1913, 1.43 km2 in 1945, 0.97 km2 in 1979, and 0.87 km2 in 2003. The great Sperry Glacier retreated 1.88 km2 between 1913 and 1945, and only 0.10 km2 in between 1979 and 2003. You do the math, but the rate of retreat was much greater 75 years ago than what we have witnessed in the 1979 to 2003 golden age of global warming!

Figure 3. (a) Instrumental and reconstructed summer drought for Glacier National Park. (b) Measured spring snowpack (1 May) anomalies (1922–present) and average annual instrumental and reconstructed Pacific Decadal Oscillation anomalies (1700–2000). (c) Fire area burned time line for the Glacier NP region spanning A.D. 1700–present. (d) Maps showing the decrease in area of the Sperry Glacier at critical points in time from 1850 to near present (from Pederson et al., 2006).

The authors had some interesting things to say about possible warming in the Park area in the coming decades. They note “The sole road across the crest of the Rockies in Glacier NP (the “Going-to-the-Sun Road”) is closed in the winter due to snow, and there is a substantial cost to plow and open the road each spring. The road is the economic lifeline for gateway and regional communities, generating approximately one million dollars per day in revenue when open. Thus, a longer snow-free season may not only provide local economic benefits, but also reduce costs associated with home heating and decrease the number of days of treacherous road travel.”

Rarely do we see anyone discussing the potential benefits of warming, and for this, we highly commend the Pederson et al. team.


Pederson, G.T., S.T. Gray, D,B. Fagre, and L.J. Graumlich. 2006. Long-Duration Drought Variability and Impacts on Ecosystem Services: A Case Study from Glacier National Park, Montana. Earth Interactions, 10, Paper No. 4.

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