Uncertainties that exist in the data products are the results of the
estimation and projection methods used for the assessment. Major sources of
uncertainties for baseline (1992-2005) data products include assumptions made
in structure and parameterization of specific methods and models used in the
assessment, relations and integration of these methods and models, and input
data availability and quality. The use of land- and climate-change scenarios
in the assessment, as part of the carbon modeling, is an additional source of
uncertainty for the projected (2006-2050) data products.
Because of the specific methods used in the assessment, the uncertainties
are distributed both in temporal and spatial dimensions and they vary by
product, location, and specific use. Along the temporal dimensions, mean
values of baseline and projection years should be used instead of any given
individual years. Along the spatial dimensions, data aggregated to the scale
of ecoregions should be used instead of the individual pixels or over
relatively small areas of the maps. In addition, the available multiple
models and scenarios provide users with ranges of values for a given
estimate, which may be used as a means of quantifying the spread of
uncertainties.
