We review 25+ years of published climate impacts projections for the
continental United States under a variety of climate scenarios and
compare them with observations from field and remote sensing. Summers
have become warmer and drier, fire season longer, drought stress more
severe, endemic pests more lethal, vegetation shifts obvious. We present
results from a dynamic global vegetation model that has been used since
1995 to simulate ecosystem responses to a variety of climate futures.
Strengths and weaknesses of the vegetation model and its drivers are
listed but overall results show that despite its obvious shortcomings,
the model simulated fairly well the observed trends and the order of
magnitude of the changes. One major conclusion of the study is that
uncertainty with climate and vegetation model projections is much less
than that of human choices and sociopolitical decisions which affect
land use and greenhouse gas emissions.