Climate is of course inextricably linked to patterns of land cover and land-use, particularly in a semi-arid region of such variable topography as the Colorado Plateau. The biotic communities we see today are the products of species evolution and migration over time on a constantly shifting landscape driven by changes in climate at a variety of temporal and spacial scales.
Variablility in temperature, humidity and precipitation affects biotic productivity and diversity both regionally and locally. Shifts from one climatic regime to a new pattern can be abrupt. For example, evidence from Greenland ice cores suggest that a 1300-year cold spell from 11,20010,000 years ago ended over a period of perhaps only a few years.
Dendrochronology, the study of tree growth rings, has been especially useful in understanding both long and short-term environmental variation in the Southwest. Dr. Thomas Swetnam and his colleagues at the Tree Ring Laboratory in Tucson, Arizona have been able to determine that the region is strongly influenced by a three to five-year Southern Oscillation in the Pacific ocean-atmosphere system (SO); El Niño years bring increased annual precipitation (but less rain in summer) and La Niña years bring the opposite. Short-term fluctuations such as the SO influence floods, drought cycles, fire frequencies, insect population outbreaks and pulses of tree reproduction.
Combined data from geology, paleobotany, and dendrochronology studies from many sites on the Colorado Plateau permit an approximate reconstruction of its long-term climate history. Fossil pollen and plant macrofossil studies by paleoecologist Scott Anderson have recorded dramatic vegetation changes over time at Potato Lake, a high elevation site (7,500 feet) on the Mogollon Rim. In the mid-Wisconsin Period (35,00021,000 B.P.) the area was dominated by mixed-conifer species; in the late-Wisconsin (21,00010,400 B.P.) the forest was nearly pure Engelmann spruce; and for the past 10,000 years newly arrived ponderosa pine has dominated the area's forests.
By examining the sediments in the exposed banks of deeply cut arroyos at Chaco Canyon, palynologist Stephen Hall has determined that before 8,000 B.P. a relatively cold and moderately wet climate prevailed; the canyons contained a mixed-conifer forest and the mesa tops a cold desert steppe. During the Altithermal Period (8,0004,000 B.P.) pinyon and juniper migrated into the area and replaced the mixed-conifer forests; warm desert grasses replaced the sagebrush of the cold desert steppe. The cause of these vegetation changes is thought to have been the arrival under generally warmer conditions of a monsoonal circulation with warm wet summers. A cooler and dryer Neoglacial Period lasted from 5,000 to 2,000 B.P.
The climate of the past 2,000 years includes several notable global events including the Medieval Warm Period from 1000 to 1350 A.D. and the Little Ice Age from about 1450 to 1850 A.D. Both are implicated in the mystery of the Anasazi collapse at the close of the thirteenth century. In the Southwest, higher average summer temperature and precipitation persisted from 9501130 A.D. and prolonged summer droughts occurred from 11301180 A.D.
In modern times the decade of the 1950s was notable for the severity of drought conditions throughout the Southwest, although Henri Grissino-Mayer's tree ring data at Malpais National Monument in northwestern New Mexico are evidence that the past two centuries have been the wettest period of the past 1,500 years in that region. Grissino-Mayer's data also suggest that the past 20 years have been the wettest of all, with rainfall 23 percent above the long-term New Mexico average. The implication of this and other long-term climate data is that the farms, cities and irrigation networks of the modern Southwest were built on rivers swollen by unusually wet weather. Vegetation in such critical watersheds as the Rio Grande and Colorado River basins is apt to change in the near future.
The future impacts of climate on the Colorado Plateau are complicated by current and projected global warming and intensified land use. Although global temperature fluctuates considerably from year to year due to chaotic variability of the atmosphere and ocean, there has been a long-term global warming trend underway since the early 1960s. Researchers at the NASA Goddard Institute for Space Studies who analyze data collected from several thousand meteorological stations around the world report that 1998 was the warmest year on record. Global surface temperatures in 1999 fell back from the 1998 record setting high level, with 1999 being approximately the sixth warmest year in the record. The ranking of years is approximate because of incomplete global coverage of measurement stations and small errors in the measurements.
Fire-Southern Oscillation Relations in the Southwestern United States. A close linkage between fire and climate could diminish the importance of local processes in the long-term dynamics of fire-prone ecosystems. The structure and diversity of communities regulated by fire may have nonequilibrial properties associated with variations in global climate. Successful prediction of vegetation change hinges on a better understanding of climatically driven disturbance regimes and the relative contributions of regional versus local processes to community dynamics. Adapted from a journal article by Thomas W. Swetnam and Julio L. Betancourt.
Packrat Midden Research in the Grand Canyon. On the Colorado Plateau the ice age (Pleistocene) vegetation of the Grand Canyon has been determined through the analysis of plant fossils preserved in caves and fossil packrat middens. Large changes occurred as the most recent ice age ended and the Holocene era began. Adapted by Kenneth L. Cole from his journal article.
Paleobotany and Paleoclimate of the Southern Colorado Plateau. The biota of the Colorado Plateau during the middle (50,000-27,500 B.P.) and late (27,500-14,000 B.P.) Wisconsin time periods was dramatically different from that seen today. Differences were primarily a result of major climate changes associated with the last major glacial period. This site examines the environment of the southern plateau during this time. Adapted by R. Scott Anderson from his journal article.
Agenbroad, L. D. and Mead, J. I. 1995. Documented Quaternary climate change on the Colorado Plateau: 40,000 yr B.P.-present. Pp. 3-8 In: Waugh, W. J., Petersen, K. L., Wigand, P. E., Louthan, B. D. and Walker, R. D., editors. Climate Change in the Four Corners and Adjacent Regions: Implications for Environmental Restoration and Land-use Planning. U.S. Department of Energy: CONF-9409325, National Technical Information Service, Springfield, VA.
Allen, B. D. and Anderson, R. Y. 1993. Evidence from western North America for rapid shifts in climate during the last glacial maximum. Science 260: 1920-1923.
Allen, C. D., Betancourt, J. L. and Swetnam, T. W. 1998. Landscape changes in the southwestern United States: Techniques, long-term data sets and trends. Pp. 71-84 In: Sisk, T. D., editor. Perspectives on the Land Use History of North America: A context for understanding our changing environment. Biological Science Report USGS/BRD/BSR-1998-0003. U.S. Geological Survey, Biological Resources Division, Reston, VA. Also available online: <http://biology.usgs.gov/luhna/chap9.html>
Anderson, R. S. 1993. A 35,000 year vegetation and climate history from Potato Lake, Mogollon Rim, Arizona. Quaternary Research 40: 351-359.
Anderson, R. S., Betancourt, J. L., Mead, J. I., Hevly, R. H. and Adam, D. P. 1999. Middle- and Late Wisconsin paleobotanic and paleoclimatic records from the southern Colorado Plateau, USA. Palaeogeography, Palaeoclimatology, Palaeoecology 154 (1/2).
Betancourt, J. L. 1984. Late Quaternary plant zonation and climate in southeastern Utah. Great Basin Naturalist 44: 1-35.
Betancourt, J. L., Pierson, E. A., Aasen-Rylander, K., Fairchild-Parks, J. A. and Dean, J. S. 1993. Influence of history and climate on New Mexico pinyon-juniper woodlands. Pp. 42-62 In: Aldron, E. F. and D.W.Shaw, editors. Managing pinyon-juniper ecosystems for sustainability and social needs: Proceedings of the symposium, Santa Fe, NM, April 26-30. General Technical Report RM-236. USDA Forest Service, Fort Collins, CO.
Birks, H. J. B. 1981. The use of pollen analysis in the reconstruction of past climates: a review. Pp. 111-138 In: Wigley, T. M. L., Ingram, M. J. and Farmer, G., editors. Climate and History. Cambridge University Press, New York, NY.
Bull, W. B. 1991. Geomorphic Responses to Climatic Change. Oxford University Press, New York, NY.
Davis, O. K. 1994. The correlation of summer precipitation in the Southwestern U.S.A. with isotopic records of solar activity during the Medieval Warm Period. Climatic Change 26: 271.
Dean, J. S. and Funkhouser, G. S. 1995. Dendroclimatic reconstructions for the southern Colorado Plateau. In: Waugh, W. J., editor. The Four Corners Region: Implications for Environmental Restoration and Land-Use Planning. U.S. Department of Energy, Grand Junction Projects Office, Grand Junction, CO.
Diaz, H. F. and Anderson, C. A. 1995. Precipitation trends and water consumption related to population in the southwestern United States: A reassessment. Water Resources Research 31.
Ely, L. L., Enzel, Y., Baker, V. R. and Cayan, D. R. 1993. A 5,000-year record of extreme floods and climate change in the southwestern United States. Science 262: 410-412.
Friedman, I., Carrara, P. and Gleason, J. 1988. Isotopic evidence of Holocene climatic change in the San Juan Mountains, Colorado. Quaternary Research 30: 350-353.
Fritts, H. C. 1976. Tree rings and climate. Academic Press, New York, NY, 567 pp.
Gillepsie, W. B. 1985. Holocene climate and environment of Chaco Canyon. Pp. 13-46 In: Mathien, F. J., editor. Environment and Subsistence of Chaco Canyon, New Mexico. Publications in Archaeology 18E, Chaco Canyon Studies. National Park Service, Albuquerque, NM.
Grissino-Mayer, H., Swetnam, T. W. and Adams, R. K. 1997. The rare, old-aged conifers of El Malpais: Their role in understanding climatic change in the American Southwest. Pp. 155-161 In: Mabery, K., editor. Natural history of El Malpais National Monument. Bulletin 156. New Mexico Bureau of Mines and Mineral Resources, Socorro, NM.
Grove, J. M. 1988. The Little Ice Age. Methuen, London, England.
Hack, J. T. 1942. The changing physical environment of the Hopi Indians of Arizona. XXXV; No. 1. Harvard University, Cambridge, MA, 100 pp.
Hall, S. A. 1990. Holocene landscapes of the San Juan Basin, New Mexico; geomorphic, climatic, and cultural dynamics. Pp. 323-334 In: Lasca, N. P. and Donahue, J., editors. Archaeological Geology of North America. Centennial Special Volume 4. Geological Society of America, Boulder, CO.
Hall, D. O. and Scurlock, J. M. O. 1991. Climate change and productivity of natural grasslands. Annals of Botany 67: 49-55.
Hereford, R. 1983. Effect of climate and a geomorphic threshold on the historic geomorphology and alluvial stratigraphy or the Paria and Little Colorado rivers, southwest Colorado Plateaus. Pp. 247 In: Wells, S. G., Love, D. W. and Gardner, T. W., editors. Chaco Canyon country. American Geomorphological Field Group, Albuquerque, NM.
Hereford, R. and Webb, R. H. 1992. Historic variation of warm-season rainfall, southern Colorado Plateau, southwestern U.S.A. Climate Change 22: 239-256.
Hevly, R. H. 1988. Prehistoric vegetation and paleoclimates on the Colorado Plateaus. Pp. 93-118 In: Gumerman, G. J., editor. The Anasazi in a Changing Environment. Cambridge University Press, New York, NY.
Jacobs, B. F., Fall, P. F. and Davis, O. K., editors. 1985. Late Quaternary Vegetation and Climates of the American Southwest. Contributions Series Number 16. American Association of Stratigraphic Palynologists, Houston, TX, 185 pp.
Kutzbach, J. E. and Webb, T. 1993. Conceptual basis for understanding Late-Quaternary climates. Pp. 5-11 In: Wright, H. E., Jr., Kutzback, J. E., Webb, T., Ruddiman, W. F. I., Street-Perrot, F. A. and Bartlein, P. J., editors. Global Climates since the Last Glacial Maximum. University of Minnesota Press, Minneapolis.
LaMarche, V. C., Jr. 1984. Increasing atmospheric carbon dioxide: tree ring evidence for growth enhancement in natural vegetation. Science 225: 1019-1021.
Martin, P. S. 1963. The Last 10, 000 Years: A Fossil Pollen Record of the American Southwest. The University of Arizona Press, Tucson.
Mast, J. N., Veblen, T. T. and Linhart, Y. B. 1998. Disturbance and climatic influences on age structure of ponderosa pine at the pine/grassland ecotone, Colorado Front Range. Journal of Biogeography 25: 743-755.
Meko, D., C., Stockton, W. and Boggess, W. R. 1995. The tree-ring record of severe sustained drought. Water Resources Bulletin 31.
Mitchell, V. 1976. The regionalization of climate in the western United States. Journal of Applied Meteorology 15: 920-927.
Mock, C. J. 1996. Climatic controls and spatial variations of precipitation in the western United States. Journal of Climate 9: 1111-1125.
Molles, M. C., Jr. and Dahm, C. N. 1990. A perspective on El Niño and La Niña: global implications for stream ecology. Journal of the North American Benthological Society 9: 68-76.
Neilson, R. P. 1993. Ecotone response to climate change. Ecological Applications 3: 385-395.
NOAA. National Climatic Data Center. <http://www.ncdc.noaa.gov/> 8/1.
Pearman, G. I., Francey, R. J. and Fraser, P. J. B. 1976. Climatic implications of stable carbon isotopes in tree rings. Nature 260: 771-773.
Pearson, G. A. 1931. Forest types in the southwest as determined by climate and soil.Technical Bulletin 247. USDA Forest Service, Washington, D.C., 27 pp.
Petersen, K. L. 1988. Climate and the Dolores River Anasazi: A Paleoenvironmental Reconstruction from a 10,000-Year Pollen Record, La Plata Mountains, Southwestern Colorado. University of Utah Press, Salt Lake City.
Peterson, K. L. 1994. Modern and Pleistocene climatic patterns in the west. In: Harper, K., Clair, L. L. S., Thorne, k. H. and Hess, W. M., editors. Natural History of the Colorado Plateau and Great Basin. University Press of Colorado, Niwot, CO.
Pieper, R. D. 1994. Ecological implications of livestock grazing. Pp. 177-211 In: Vavra, M., Laycock, W. A. and Pieper, R. D., editors. Ecological implications of livestock herbivory in the West. Society for Range Management, Denver, CO.
Reneau, S. L., McDonald, E. V., Gardner, J. N., Kolbe, T. R., Carney, J. S., Watt, P. M. and Longmire, P. A. 1996. Erosion and deposition on the Pajarito Plateau, New Mexico: Geomorphic responses to late Quaternary climatic change. New Mexico Geological Society Guidebook, 47th Field Conference, Jemez Mountains Region, New Mexico Geological Society, 484 pp.
Richmond, A. J., Jr. 1987. Historic precipitation sequences on the Colorado Plateau, 1859-1983. M.S. Thesis. Northern Arizona University, Flagstaff, AZ.
Sellers, W. D. and Hill., R. H., editors. 1974. Arizona Climate, 1931-1972. University of Arizona Press, Tucson, AZ.
Shafer, D. S. 1989. The timing of late Quaternary monsoon precipitation maxima in the southwest United States. Ph.D. Dissertation. University of Arizona, Tucson.
Stute, M. J., Clark, F., Schlosser, P. and Broecker, W. S. 1995. A 30,000 yr continental paleotemperature record derived from noble gases dissolved in groundwater from the San Juan Basin, New Mexico. Quat. Res. 43: 209-220.
Swetnam, T. W. and Betancourt, J. L. 1990. Fire-Southern Oscillation relations in the southwestern United States. Science 249: 1017-1021.
Swetnam, T. W. 1990. Fire history and climate in the Southwestern United States. Pp. 6-17 In: Krammes, S. J., editor. Proceedings of Symposium on Effects on Fire in Management of Southwestern Natural Resources. General Technical Report RM-191. U.S. Forest Service.
Swetnam, T. W. and Betancourt, J. L. 1990. Fire-Southern Oscillation relations in the southwestern United States. Science 249: 1017-1021.
Swetnam, T. W. and Betancourt, J. L. 1992. Temporal patterns of El Niño/Southern Oscillation - wildfire teleconnections in the southwestern United States. Pp. 259-270 In: Diaz, H. F. and Markgraf, V., editors. Historical and Paleoclimatic Aspects of the Southern Oscillation. Cambridge University Press, New York, NY.
Swetnam, T. W. and Lynch, A. M. 1993. Multi-century, regional-scale patterns of western spruce budworm history. Ecological Monographs 63: 399-424.
Thompson, R. S., Whitlock, C., Bartlein, P. J., Harrison, S. P. and Spaulding, W. G. 1993. Climatic changes in the western United States since 18,000 yr B.P. Pp. 468-513 In: H.E. Wright, J., Kutzbach, J. E., III, T. W., Ruddiman, W. F., Street-Perrott, F. A. and Bartlein, P. H., editors. Global Climates since the last glacial maximum. University of Minnesota Press, Minneapolis.
Thompson, R. S. Past Climate and Vegetation Changes in the Southwestern United States. <http://geochange.er.usgs.gov/sw/impacts/biology/pastclim/> 2/25/99.
Touchan, R., Allen, C. D. and Swetnam, T. W. 1996. Fire history and climatic patterns in ponderosa pine and mixed-conifer forests of the Jemez Mountains, northern New Mexico. Pp. 179-195 In: Allen, C. D., editor. Fire Effects in Southwestern forests: Proceedings of the Second La Mesa Fire Symposium. General Technical Report RM-286. USDA Forest Service, Fort Collins, CO.
U.S. Department of Commerce. 1968. Climatic atlas of the United States. Environmental Science Services Administration, Environmental Data Service, 80 pp.
U.S. Geological Survey. Impacts of Climate Change and Land Use on the Southwestern U.S. <http://climchange.cr.usgs.gov/info/sw/index.html> 9/7/00.
Van Devender, T. R. and Spaulding, W. G. 1979. Development of climate and vegetation in the southwestern United States. Science 204: 701-710.
Van West, C. R. 1991. Reconstructing prehistoric climatic variability and agricultural production in southwestern Colorado, A.D. 901-1300: A GIS approach. Pp. 25-34 In: Hutchinson, A., Smith, J. E. and Usher, J., editors. Proceedings of the Anasazi Symposium 1991. Mesa Verde Museum Association, Inc., Mesa Verde, CO.
Vitousek, P. M. 1994. Beyond global warming: ecology and global change. Ecology 75: 1861-1876.
Waugh, W. J., Petersen, K. L., Wigand, P. E., Louthan, B. D. and Walker, R. D. 1995. Climate Change in the Four Corners and Adjacent Regions: Implications for Environmental Restoration and Land-use Planning. U.S. Department of Energy, CONF-9409325, National Technical Information Service, Springfield, VA, 196 pp.
Webb, T. I. 1986. Is vegetation in equilibrium with climate? How to interpret late Quaternary pollen data. Vegetatio 67: 75-91.
Weng, C. and Jackson, S. 1999. Late-glacial and Holocene vegetation history and paleoclimate of the Kaibab Plateau, Arizona. Palaeogeography, Palaeoclimatology, Palaeoecology.
Withers, K. and Mead, J. I. 1993. Late Quaternary vegetation and climate in the Escalante River basin on the central Colorado Plateau. Great Basin Naturalist 53: 145-161.