simulating the response of two wyoming glaciers to projected 21 rst century warming
DESCRIPTION
Simulating the Response of Two Wyoming Glaciers to Projected 21 rst Century Warming. Mitchell A. Plummer, Idaho National Laboratory L. DeWayne Cecil U.S.Geological Survey. Teton Range. Wind River Range. Net annual ice balance, b n. b n = net ice budget at any location in the x,y plane - PowerPoint PPT PresentationTRANSCRIPT
Simulating the Response of Two Wyoming Glaciers to Projected 21rst Century Warming
Mitchell A. Plummer,Idaho National Laboratory
L. DeWayne CecilU.S.Geological Survey
Te
ton
Ran
ge
Wind River Range
Net annual ice balance, bn
• bn = net ice budget at any location in the x,y plane
• Snow = total snowfall
– Fraction of precipitation falling as snow
• M = mass of snow melted
– Calculated from energy balance when T > 0
• E = evaporation & sublimation
– Calculated via turbulent heat transfer equations
dtEMSnowdtESnowbfall
spring
spring
falln )()(
T = -6ºC
Modeled Glaciers and Perennial Snow Mapped Glaciers and Perennial Snow
Gra
nd
Tet
on
Cas
cad
e C
anyo
n
Jenny Lake
Mo
un
t Sain
t Joh
n
Photo by Ed
Williams, BYU
Idaho
Base case
+1.0 °C+0.5 °C
Base case
+0.5ºC
+1.0ºC
+1.5ºC
+2.0ºC
+2.5ºC
Upper Fremont Glacier
LowerFremont Glacier
Knifepoint Glacier
Titcomb basin
August 1990
firn line,3980 m
Naftz et al. 2002
-350
-300
-250
-200
-150
-100
-50
0
50
100
0 100 200 300 400 500 600 700
No
rm
alize
d m
ass b
ala
nce
Elapsed time (yrs)
0
2e+007
4e+007
6e+007
8e+007
1e+008
1.2e+008
1.4e+008
1.6e+008
0 100 200 300 400 500 600 700
To
tal ic
e v
olu
me
(m
^3
)
Elapsed time (yrs)
Max ice thickness (m
)
40
60
80
100
120
140
160
180
200
Tota
l ic
e v
olu
me (
m3)
1. Modern glacier too large
2. Modern glacier just right (+0.25ºC)
3. Five 0.25ºC temperature
increases applied
Glacier allowed to return to
steady state
{
Conclusions• Modeling experiments suggest that a temperature increase of ~1.5°C
would effectively eliminate the Teton and Lower Fremont glaciers
– Apparent sensitivity of Fremont glacier appears inconsistent with the USGS 18O temperature record but lapse rate variations not yet explored
• At late 20th century global warming rates (~0.1°C / decade), it could take as long as 150 – 200 years to dramatically increase the biodiversity of these locations
• Global climate models scaled to the Pacific NW project an increase in average temperature on the order of 0.2°-0.6°C (0.3°-1°F) per decade throughout the 21st century, so maybe we can get to that species richness in 50 – 100 yrs.
• Response times matter. Two retreating glaciers of different size may well be responding to completely different phenomena.
• Uncertainties? Yes, but …
Questions• Barring ‘local’ redistribution of snow by wind, avalanching
etc, how variable is precipitation across short distances in the mountains and how would one capture that in a simple model?
• In paleoglacier modeling,
– How is a large change in mountain precipitation distributed vertically?
– How reasonable is it to assume constant lapse rates?
• Are pseudo-vertical lapse rates related to vertical precipitation gradients?
• Need more data to describe mountain climate and its variability
Photo by Ed Williams, BYU Idaho
Terminus