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Robert S. Thompson

Publications and source records attributed to Robert S. Thompson.

27 records · Page 2Linked to original sources
USGS2003

Quaternary vegetation and climate change in the western United States: Developments, perspectives, and prospects

This chapter explores the strengths and shortcomings of the major sources of data on Quaternary vegetation and climate change and discusses the use of models as a means to explore past and potential future environmental changes. The flora and major vegetation types of the western United States are present for several million years. Ongoing changes in atmospheric chemistry , climate, and human activities may lead to major vegetation changes over the coming decades to centuries. The combination of observations from the paleoenvironmental record, modern ecological studies, and modeling now permit assessments of the magnitude of potential future changes in the context of natural variability. They also provide opportunities for hypothesis testing and identification of the processes driving past changes in vegetation and climate. Understanding the dynamics of paleoenvironmental change can contribute to current conservation and natural resource management efforts and will help conservation and natural resource managers anticipate the potential rate, magnitude, and complexity of future vegetation change.

western United States↗
USGS2001

Potential changes in the distributions of western North America tree and shrub taxa under future climate scenarios

Increases in atmospheric greenhouse gases are driving significant changes in global climate. To project potential vegetation response to future climate change, this study uses response surfaces to describe the relationship between bioclimatic variables and the distribution of tree and shrub taxa in western North America. The response surfaces illustrate the probability of the occurrence of a taxon at particular points in climate space. Climate space was defined using three bioclimatic variables: mean temperature of the coldest month, growing degree days, and a moisture index. Species distributions were simulated under present climate using observed data (1951–80, 30-year mean) and under future climate (2090–99, 10-year mean) using scenarios generated by three general circulation models—HADCM2, CGCM1, and CSIRO. The scenarios assume a 1% per year compound increase in greenhouse gases and changes in sulfate (SO 4 ) aerosols based on the Intergovernmental Panel on Climate Change (IPCC) IS92a scenario. The results indicate that under future climate conditions, potential range changes could be large for many tree and shrub taxa. Shifts in the potential ranges of species are simulated to occur not only northward but in all directions, including southward of the existing ranges of certain species. The simulated potential distributions of some species become increasingly fragmented under the future climate scenarios, while the simulated potential distributions of other species expand. The magnitudes of the simulated range changes imply significant impacts to ecosystems and shifts in patterns of species diversity in western North America.

Ecosystems↗
USGS2000

Atlas of relations between climatic parameters and distributions of important trees and shrubs in North America; additional conifers, hardwoods, and monocots

This volume explores the continental-scale relations between climate and the geographic ranges of woody plant species in North America. A 25-km equal-area grid of modern climatic and bioclimatic parameters for North America was constructed from instrumental weather records. The geographic distributions of selected tree and shrub species were digitized, and the presence or absence of each species was determined for each cell on the 25-km grid, thus providing a basis for comparing climatic data and species' distribution.

Professional Paper↗
USGS1999

Atlas of relations between climatic parameters and distributions of important trees and shrubs in North America

This atlas explores the continental-scale relations between the geographic ranges of woody plant species and climate in North America. A 25-km equal-area grid of modern climatic and bioclimatic parameters was constructed from instrumental weather records. The geographic distributions of selected tree and shrub species were digitized, and the presence or absence of each species was determined for each cell on the 25-km grid, thus providing a basis for comparing climatic data and species distributions. The relations between climate and plant distributions are explored in graphical and tabular form. The results of this effort are primarily intended for use in biogeographic, paleoclimatic, and global-change research.

Professional Paper↗
USGS1998

Paleoclimate simulations for North America over the past 21,000 years: Features of the simulated climate and comparisons with paleoenvironmental data

Maps of upper-level and surface winds and of surface temperature and precipitation illustrate the results of a sequence of global paleoclimatic simulations spanning the past 21,000 yr for North America. We review (a) the large-scale features of circulation, temperature, and precipitation that appear in the simulations from the NCAR Community Climate Model Version 1 (CCM 1), (b) the implications of the simulated climate for the past continental-scale distributions of three plant taxa ( Picea spp., Pseudotsuga menziesii , and Artemisia tridentata ), which are broadly representative of the vegetation across the continent, and (c) the potential explanations in terms of atmospheric circulation or surface energy- and water-balance processes for mismatches between the simulations and observations. Most of the broad-scale features of previous paleoclimatic simulations with the NCAR CCM 0 for North America are present in the current simulations. Many of the elements of a conceptual model (based on previous climate simulations) that describes the controls of paleoclimatic variations across North America during the past 21,000 yr are found in simulations reviewed here. These include (1) displacement of the jet stream by the Laurentide Ice Sheet to the south of its present position in both winter and summer, (2) generation of a ‘glacial anticyclone’ over the ice sheet at the LGM, and the consequent induction of large-scale sinking motions induced over eastern North America, (3) changes in the strength of surface atmospheric circulation features through time, including weakening of the Aleutian low in winter, and strengthening of the eastern Pacific and Bermuda high-pressure systems in summer as the ice sheet decreased in size, (4) development of a ‘heat low’ at the surface and a strengthened ridge in the upper-atmosphere over the continent at the time of the maximum summer insolation anomaly, (5) increases in summer temperature earlier in regions remote from the ice sheet (these increases appear earlier in the present (CCM 1) simulations than in the previous (CCM 0) ones, however), and (6) continuation of negative winter temperature anomalies into the middle Holocene. In general, simulated surface conditions that are discordant with paleoenvironmental observations can be attributed to the simulation of particular atmospheric circulation patterns (e.g. those that suppress precipitation or advect warm air into a region), with these mismatches amplified in Beringia and the southeastern United States by surface energy- and water-balance processes.

Quaternary Science Reviews↗
USGS1996

Middle Pliocene vegetation: Reconstructions, paleoclimatic inferences, and boundary conditions for climate modeling

The general characteristics of global vegetation during the middle Pliocene warm period can be reconstructed from fossil pollen and plant megafossil data. The largest differences between Pliocene vegetation and that of today occurred at high latitudes in both hemispheres, where warming was pronounced relative to today. In the Northern Hemisphere coniferous forests lived in the modern tundra and polar desert regions, whereas in the Southern Hemisphere southern beech apparently grew in coastal areas of Antarctica. Pliocene middle latitude vegetation differed less, although moister-than-modern conditions supported forest and woodland growth in some regions now covered by steppe or grassland. Pliocene tropical vegetation reflects essentially modem conditions in some regions and slightly cooler-than-or warmer-than- modern climates in other areas. Changes in topography induced by tectonics may be responsible for many of the climatic changes since the Pliocene in both middle and lower latitudes. However, the overall latitudinal progression of climatic conditions on land parallels that seen in the reconstruction of middle Pliocene sea-surface temperatures. Pliocene paleovegetational data was employed to construct a 2 ° × 2 ° global grid of estimated mid-Pliocene vegetational cover for use as boundary conditions for numerical General Circulation Model simulations of middle Pliocene climates. Continental outlines and topography were first modified to represent the Pliocene landscape on the 2 ° × 2 ° grid. A modern 1 ° × 1 ° vegetation grid was simplified and mapped on this Pliocene grid, and then modified following general geographic trends evident in the Pliocene paleovegetation data set.

Marine Micropaleontology↗
USGS1996

Pliocene and early Pleistocene environments and climates of the western Snake River Plain, Idaho

Sedimentological, palynological, and magnetic susceptibility data provide paleoenvironmental and paleoclimatic information from a 989 ft (301 m) core of sediments from the upper Glenns Ferry and Bruneau Formations from near the town of Bruneau in Owyhee County, Idaho. Chronology is based on stratigraphic position, paleomagnetism, and biostratigraphic data, which collectively suggest a late Gauss Normal-Polarity Chron age for the Glenns Ferry sediments and a middle Matuyama Reversed-Polarity Chron age for the Bruneau sediments. A deep lake was present on the western Snake River Plain during the portions of the time represented by the Glenns Ferry Formation, and the mudstones of the lower half of the core were apparently deposited in this lake. The terminal regression of the Glenns Ferry lake may be represented in the Bruneau core by sandy mudstones and sands that overlie the deep-water mudstones. A cobble layer present in the core between the Glenns Ferry lake beds and those of the overlying Bruneau Formation may indicate through-flow by the ancestral Snake River. Palynological data from the Glenns Ferry sediments in the Bruneau core reveal a pollen flora similar to the modern regional pollen flora, with very rare occurrences of now-extirpated taxa common earlier in the Tertiary. Palynological data from the Pliocene portion of this core indicate conditions more moist than today, with cooler summers and perhaps warmer winters. Quasi-periodic fluctuations in coniferous pollen (primarily Pinus) versus arid steppe taxa (primarily Chenopodiaceae/ Amar-anthus ) indicate significant variations in moisture through the lower two-thirds of the Glenns Ferry portion of the core. Shorter wave-length fluctuations in magnetic susceptibility and (inversely) Artemisia may reflect variations in temperature or other unidentified climatic variables. The pollen spectra from the Bruneau Formation sediments in the Bruneau core are dominated by Artemisia and resemble those of the Wisconsinan glacial period on the Snake River Plain, and hence indicate cold and dry conditions during some portion of the early Pleistocene. The deep-water Glenns Ferry lacustrine episode appears to date between approximately 3.5 to 3.3 and 2.5 Ma, and thus occurred during the middle Pliocene period of warmer-than-modern global temperatures. Similar sustained wetter-than-present conditions occurred in the same age range at sites across the western U.S.A. from southern California and Arizona to northern California and Idaho. This moist period was apparently followed by an interval of regional arid conditions that persisted for several hundred thousand years.

Idaho↗
USGS1994

Joint investigations of the Middle Pliocene climate I: PRISM paleoenvironmental reconstructions

The Pliocene epoch represents an important transition from a climate regime with high-frequency, low-amplitude oscillations when the Northern Hemisphere lacked substantial ice sheets, to the typical high-frequency, high-amplitude Middle to Late Pleistocene regime characterized by glacial—interglacial cycles that involve waxing and waning of major Northern Hemisphere ice sheets. Analysis of middle Pliocene (∼3 Ma) marine and terrestrial records throughout the Northern Hemisphere forms the basis of an integrated synoptic Pliocene paleoclimate reconstruction of the last significantly warmer than present interval in Earth history. This reconstruction, developed primarily from paleontological data, includes middle Pliocene sea level, vegetation, land—ice distribution, sea—ice distribution, and sea-surface temperature (SST), all of which contribute to our conceptual understanding of this climate system. These data indicate middle Pliocene sea level was at least 25 m higher than present, presumably due in large part to a reduction in the size of the East Antarctic Ice Sheet. Sea surface temperatures were essentially equivalent to modern temperatures in tropical regions but were significantly warmer at higher latitudes. Due to increased heat flux to high latitudes, both the Arctic and Antarctic appear to have been seasonally ice free during the middle Pliocene with greatly reduced sea ice extent relative to today during winter. Vegetation changes, while more complex, are generally consistent with marine SST changes and show increased warmth and moisture at higher latitudes during the middle Pliocene.

Global and Planetary Change↗