NORTH CASCADE RESPONSE TO GLOBAL WARMING
 

Mauri S. Pelto, Director NCGCP
Nichols College, Dudley, MA 01571 mspelto@nichols.edu

Snowpack

Snowpack charts

Ice Worms

Ice Worm Charts
Mass Balance

Mass balance Data Set

Terminus Behavior

Terminus Data Set

Glacier Runoff

Glacier runoff  charts

Updated 6/15/09
Home Page

Impact of global warming on Glacier Termini and Survival: I read in the 2002 North Cascades National Park-Natural Notes that: " More than 90 percent of the North Cascades glaciers could disappear within 40 years if the annual temperature increases by 2 degrees Celsius (3.6 degrees Fahrenheit)."  We have observed the response of North Cascade glaciers to a climate change of nearly this magnitude at the end of the Little Ice Age and did not lose nearly 90% of the glaciers, nor did most of them finish their retreat, adjusting to the post Little Ice Age climate in less than 40 years.  Thus, this figure is not correct.  Annual mass balance surveys on ten glaciers in the North Cascades indicate that North Cascade glaciers have lost an average of 0.5 m of thickness each year from 1984-2007.  This 13-14 m of glacier thickness lost is approximately 20-40 % of the entire volume of North Cascade glaciers, gone in twenty four years.  The result is incredible changes in the size of our glaciers due to the warmer climate. What climate changes have we observed? What do recent trends suggest about the likely future of North Cascade glaciers?  

Examples of Glacier change from around the globe.

Above is the ratio of  April 1  snowpack water equivalent to total precipitation at Concrete and Diablo Dam. The declining ratio indicates that more precipitation is not accumulating as snow either because it fell as rain or some of the snowpack has melted. The observed rise in ablation season temperature since 1946 at Diablo Dam and snowpack decline at the five long term USDA snow measurement stations in the North Cascades.  The snowpack decline since 1976 has been minor.
Change in mean precipitation, temperature and snowpack for the Dec-Feb. period at Darrington, Diablo Dam and Concrete 1935-2007.  Snowpack has decline markedly, while temperature and precipitation have increased. Whitechuck Glacier in 1973 and 2006, indicating the complete loss of the north branch of this glacier.

Observed Climate Changes: As the above figures illustrates April 1 snowpack in the North Cascades observed at 8 USDA Snow Course-Snotel sites has declined by 25% from 1946-2006.  This is despite  a 3% increase in precipitation.  Thus warmer temperatures in the winter are leading to more rain events and more melt events.  With less snowpack as melt season begins the glaciers are then faced with warmer summer temperatures as shown below as well.  Since 1976 snowpack has not diminished on April 1 despite a marked rise in winter precipitation. Temperatures have risen 0.9 C during the last century in the North Cascades.  The 1990's were the warmest decade of the century. 

Below is Foss Glacier in 1988 and 2005 after losing 40% of its area in the last 25 years.

First, a 1.5-2.0 warming following the Little Ice Age led to retreat of all North Cascade glaciers.   North Cascade glaciers lost 35-50% of their volume in the last century and a somewhat lesser amount of glacier area (Pelto and Hedlund, 2001).  There are a significant number of glaciers in the North Cascades that have not fully adjusted to the post Little Ice Age climate, thus their response time can be as much as a century.    North Cascade glacier response to climate change fall into three groups

1) Retreat from the Little Ice Age (LIA) to approximately 1950 followed by a period of advance from 1950-1976, and then retreat since 1976.

2) Rapid retreat from the LIA to approximately 1950, slow retreat or equilibrium from 1950-1976, and moderate to rapid retreat since 1976. 

3) Continuous retreat from the LIA to the present.  

These types reflect different physical characteristics.  In the future it is type 3 glaciers that are likely to disappear in the next 10-50 years, these comprise 65-70% of all North Cascade glaciers including almost all of the small and east side glaciers.  Type 2 glaciers which are slowly retreating will last longer typically more than 50 years, these comprise 20% of North Cascade glaciers.  Many of these glaciers would survive as much smaller versions.  And finally Type 1 glaciers which were healthy with the climate of the 1960's and tend to be the larger glaciers will last much longer, and comprise most of the surviving glaciers.  This group represent 10-15% of North Cascade glaciers, but represent most of the large popular named glaciers.  This group accounts for 35% of the total current glacier area.  Thus, we would likely see the loss of up to 65-75% of North Cascade glaciers due to a 2OC warming, but most will take well over 40 years to disappear. 

The best way to identify if a glacier will survive is to examine its changes in thickness over time along a centerline profile.  If the glacier is thinning significantly along its entire length it has no point to retreat to where it can reestablish equilibrium and thus it is in disequilibrium with climate and will melt away.

For example, Easton Glacier a Type 1 has lost 46 m of ice thickness between 1916 and 1984, and 13 m between 1984 and 2002.  Its terminus has retreated a net distance of 2123 m, although it advanced more than 600 m from 1950-1980.   This retreat was a 30% reduction in overall glacier length.  The glacier is thinning only slightly in the accumulation zone, and will be able to retreat to a new stable position.  

Lyman Glacier a Type 3 glaciers has lost 65 m of ice thickness since the Little Ice Age, and has retreated 1500 m without nearing equilibrium.  This retreat represents a 70% decline in the length of the glacier.  This glacier continues to adjust to the post Little Ice Age climate, thinning substantially along its entire length and will not survive in the present climate.  

Columbia Glacier a Type 2 glacier has In contrast the  This glacier has retreated slowly but steadily during the last half century.  The ice thickness has been reduced by 55m since the Little Ice Age.  The glacier continues to lose thickness most rapidly in the accumulation zone.  This is not the sign of a glacier retreating in a stable fashion.  

Mount Baker Glaciers As noted at right the glaciers on Mount Baker retreated during the early part of the century, advanced near the middle of the century and have retreated since 1980, at an increasing rate.

 

 

 

 

 

 

 

Impact on Glacier Runoff: The importance of this glacier retreat is the change in water resources.  In the North Cascades of Washington,  700 glaciers yield 900 million m3 of runoff each summer, glacier retreat means less glacier runoff.  Thus, the loss of 30-50% of glacier area in the last century has reduced summer streamflow from glaciers by a commensurate amount.  Further that continued retreat will further reduce summer streamflow which comprises a substantial share of flow in many rivers in the North Cascades.  

1)Alpine runoff throughout the mountain range is increasing in the winter (Nov.-Mar.), as more frequent rain on snow events enhance melting and reduce snow storage  Streamflow has risen 18% in Newhalem Creek and 19% in Thunder Creek despite only a slight decrease, 1% in winter precipitation at Diablo Dam, within 5 km of both basins.  The enhanced winter melt is evident in the 25% reduction in April 1 SWE at USDA Snotel sites.

2)Spring runoff (April-June) has increased in both basins by 5-10% due to earlier alpine snowpack melting. 

3)Summer runoff has decreased markedly, 27%, in the non-glacier Newhalem basin with the earlier melt of reduced winter snowpack.  In Thunder basin runoff has in contrast increased negligibly, 4%.  The difference is accounted for in part by enhanced glacier melting.   The observed net loss of -0.52 m/a in glacier mass spread over the melt season is equivalent to 2.45 m3/s in Thunder Basin,  which is 10% of the mean summer streamflow.  This trend of enhanced summer streamflow by reduction in glacier volume will not continue as the extent of glaciers continues to decline.   

          

Advancing  

Stationary

Retreating

North Cascades  

 

 

 

1975                        

14

11

22

1985                         

  5

10

32

2005                        

  0

  0

47

Switzerland

 

 

 

1975                        

70

  3

28

1985                        

42

  9

13

2005

 0

2

76

Italy

 

 

 

1980                        

25

10

10

1985                        

25

  6

14

2005                       

  0

  1

71

Patagonia

 

 

 

1975                         

  4

  1

24

2000                        

  1

  3

25

Table 3.  Alpine glacier termini are recognized by the IPCC as one of the most sensitive indicators of climate.  The terminus behavior of alpine glaciers indicate increasing retreat on the smaller alpine glaciers of the North Cascades, Washington and the Alps of Italy and Switzerland since 1975.  On larger Patagonia glacier, glacier retreat is ongoing, but not significantly increasing, since these glaciers respond more slowly to climate change, in this case the warming that began after 1975 ( Pelto and Miller, 2000)