Paleoclimatic reconstructions for the Nevada Test Site, spanning the last 45,000 years, are based on plant macrofossil assemblages from radiocarbonated packrat (Neotoma spp) middens from south-central Nevada. The temperature regime during the Wisconsin glacial age, from before about 45,000 years ago until about 12,000 years ago, was characterized by lower temperatures during all seasons. Wisconsin maximum (about 18,000 years before present) winter temperatures were at least 6 deg. Celsius below those of the present, and the relative decrease in summer temperature was as much as 8 deg. Celsius. The data provide evidence for a precipitation regime drier than that proposed by many studies. The maximum estimated increase in average annual precipitation during the full-glacial period is 40 percent above current precipitation. The increase in temperature signaling the end of the Wisconsin glacial age may have begun as early as about 16,000 years ago. The oldest record of desert scrub vegetation from the Nevada Test Site area dates to about 15,000 years ago. By 10,000 years before present, average annual temperatures may have approximated present values, although seasonal temperature and precipitation regimes probably differed from those of today. Climate changes during the last 10,000 years have been relatively minor variations in a warm, dry climatic regime. Probably future climatic changes include a brief but pronounced warm period within the next 500 years, followed by a protracted transition to the next glacial age during the next 10,000 years. (USGS)
