Planetary and synoptic-scale atmospheric features are important because they set the stage for differing climate regimes in the Yucca Mountain area—whether in past, present, or future time. Climate proxy records in the region show that numerous climate regimes occurred during the past 800 k.y. ranging from warm interglacial periods (similar to modern climate) to cool or cold and wet glacial periods. The current climate at Yucca Mountain is arid, with an annual average precipitation of ∼17.7 cm/yr. Most of the annual precipitation occurs during winter or during July and August monsoons. Annual average temperatures generally range from 15° to 18 °C but can exceed 40 °C during summer. Continuously deposited calcite at Devils Hole, Nevada, provides a precise chronology that can be used to calibrate other climate proxy data that provide estimates of the nature and magnitude of past climate events. During past glacial periods, mean annual temperature may have been as much as 10° to 15 °C cooler than present temperatures, with mean annual precipitation as much as 1.4–3 times present precipitation. These records of past climate are used to bound estimates of future climate to assess future potential infiltration. Five maximum infiltration scenarios are estimated to occur within the next 500 k.y. providing that anthropogenic disturbance does not modify or alter long-term climate change.

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