YUCCA MOUNTAIN CLIMATE: PAST, PRESENT, AND FUTURE

Modern climate historical summaries for the Yucca Mountain area and western U.S. stations are located at http://www.yuccamountain.dri.edu/ and http://www.wrcc.dri.edu/climsum.html, respectively. The present-day arid interglacial climate of the Yucca Mountain area can be understood in terms of global-scale atmospheric circulation and regional-to-local physiographic features. In general terms, the area is under the influence of mid-latitude westerly winds and associated storm systems during the cool part of the year and is under the influence of moist air advected from the eastern tropical Pacific Ocean and Gulf of California during the summer. Climate change over the past several hundred thousand years can be partially understood in terms of changes in these atmospheric circulation patterns, physiographic features, and predictable variations in the earth's orbital characteristics.

Regional and local evidence indicates that the Yucca Mountain site has experienced many different climate states, ranging from glacial to interglacial periods, over the past several hundred thousand years. Proxy records from the past 800,000 years suggest that climate may be grouped into four primary climate states: interglacial, monsoon, intermediate, and glacial. Each climate state has a different level of effective moisture (commonly defined as precipitation minus evaporation, thus temperature is important). Glacial and intermediate climate states were periods of sustained greater effective moisture with greater infiltration and recharge than the present interglacial period.

Past climate change can be timed using the Earth's orbital parameters: eccentricity and precession. Comparison of the Devils Hole, NV, d¹⁸O and age data (approximately 568,000 to 60,000 years B.P.) with the orbital parameters and age data suggests a formal relation between the timing of climate change and the precession parameter. The relation between climate change and precession in the past provides the basis to use a precessional clock to time climate change in the future. Climate proxy data from the Owens Lake, CA, sedimentary record provides a relative magnitude scale for past climate states. These records form the basis for estimating the nature and timing of future climate in the Yucca Mountain area.