Data-Model Comparisons
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Climate Model Comparisons |
Global climate models are now being enlarged to earth-system models in
which the vegetation and ocean models are coupled to the climate models. These models are
powerful tools for simulating past changes in climate, vegetation, and hydrological
conditions. The simulations show how the changing controls on climate from seasonal
insolation, carbon dioxide concentrations, and ice sheet size may have affected regional
and continental climate and environmental patterns. Large sets of pollen and
lake-level data now exist for checking the results of these models, and Brown researchers
have pioneered in interpreting and analyzing these data and using them to test the model
simulations. One of the first tasks of COHMAP (Cooperative Holocene Mapping Project) was
to assemble a global set of data for the last glacial maximum (LGM, which was 18,000
radiocarbon years ago or 21,000 calendar years ago) to check the initial climate modeling
simulations for LGM by Gates (1976, Science) and Manabe and Hahn (1977, JGR).This
Peterson et al. (1979, Quaternary Research) paper was the start to the international,
interdisciplinary, interinstitutional effort that COHMAP researchers headed up, over the
next decade, to assemble a global data base for the last 21,000 years and to use it to
test the modeling simulations by Kutzbach and others with the NCAR (National Center for
Atmospheric Research) Community Climate Model (CCM, version 0) for the time series of
climates from 21,000 year ago until present. COHMAP researchers published their results in
Science (COHMAP Members, 1988) and later in the book Global Climates Since
the Last Glacial Maximum (Wright et al., 1993) and illustrated the combined impacts
of orbital forcing, ice sheet size, and increases in carbon dioxide and sea-surface
temperatures on the global climates, vegetation, and lakes. A follow-up to these
pioneering studies has recently appeared in Quaternary Science Reviews (v. 17, nos. 6-7)
in 1998 on Late Quaternary Climates: Data Synthesis and Model Experiments with
Tom Webb as the editor. Kutzbach and other ran a new set of modeling simulations with the
NCAR CCM1, an interactive mixed-layer model for the oceans. I.Colin Prentice and Sandy
Harrison used a global biome model, BIOME1, to simulate the global patterns of biomes and
several colleagues assembled data sets from Africa, Europe, and North America to compare
to the new model results. Ben Felzer also published a part of his PhD research at Brown in
a study describing a series of climate model sensitivity experiments to separate out the
impact of ice sheets from that of carbon dioxide and orbital insolation changes on late
Quaternary climates.
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Biome
Distributions |
Current research involves use of climate estimates derived from pollen
data to test the climate-model simulations for 6,000 years ago by PMIP (Paleoclimate
Modeling Intercomparison Project). Former PhD student Jack Williams, Pat Barlein, and Tom
Webb have collaborated on that study (Williams et al., in press), which includes the two
figures on this page. Researchers at Brown have also been involved in the BIOME 6000 project to organize global sets of pollen date for mapping
biomes at 6,000 and 21,000 years ago. These paleovegetation maps are being used to test
the results of climate models coupled asynchronously to BIOME3, a global biome model
developed by Colin
Prentice and co-workers.
Coastal Studies Geoarchaeology Paleoclimates Vegetation Dynamics