Controls of Global Snow under a Changed Climate

This study assesses the ability of a newly developed high-resolution coupled model from the Geophysical Fluid Dynamics Laboratory to simulate the cold-season hydroclimate in the present climate and examines its response to climate change forcing. Output is assessed from a 280-yr control simulation that is based on 1990 atmospheric composition and an idealized 140-yr future simulation in which atmospheric carbon dioxide increases at 1% yr(-1) until doubling in year 70 and then remains constant. When compared with a low-resolution model, the high-resolution model is found to better represent the geographic distribution of snow variables in the present climate. In response to idealized radiative forcing changes, both models produce similar global-scale responses in which global-mean temperature and total precipitation increase while snowfall decreases. Zonally, snowfall tends to decrease in the low to midlatitudes and increase in the mid- to high latitudes. At the regional scale, the high- and low-resolution models sometimes diverge in the sign of projected snowfall changes; the high-resolution model exhibits future increases in a few select high-altitude regions, notably the northwestern Himalaya region and small regions in the Andes and southwestern Yukon, Canada. Despite such local signals, there is an almost universal reduction in snowfall as a percent of total precipitation in both models. By using a simple multivariate model, temperature is shown to drive these trends by decreasing snowfall almost everywhere while precipitation increases snowfall in the high altitudes and mid- to high latitudes. Mountainous regions of snowfall increases in the high-resolution model exhibit a unique dominance of the positive contribution from precipitation over temperature.