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 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

T = -6ºC

Modeled Glaciers and Perennial SnowMapped Glaciers and Perennial Snow

Grand Teton Cascade Canyon Jenny Lake Mount Saint John 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 Lower Fremont Glacier Knifepoint Glacier Titcomb basin

August 1990 firn line, 3980 m Naftz et al. 2002

Max ice thickness (m) Total ice volume (m 3 ) 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  18 O temperature record but lapse rate variations not yet explored At late 20 th 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