Simulating the Response of Two Wyoming Glaciers to Projected 21 rst Century Warming Mitchell A....

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

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