Tree Rings and Climate: Sharpening the Focus - Dendroclimatology - page 338

done by using the very large dataset of tree-ring and other annual- to bidecadal-
resolution proxy records already used by Mann et al. ( 2008 ) to reconstruct mean
Northern Hemisphere temperature (see above). Their MCA showed a tendency for
La Niña-like conditions in the tropical Pacific. The reconstructed spatial patterns
of temperature change implied particular dynamical responses of climate to natural
radiative forcing changes that would involve the El Niño/Southern Oscillation and
the North Atlantic Oscillation/Arctic Oscillation. The work of Cook et al. ( 2007 ) ,
Goosse et al. ( 2008 ) , Graham et al. ( 2007 ) , and Mann et al. ( 2009 ) represents a new
stage in the development of high-resolution paleoclimatology, including dendrocli-
matology, in which reconstructions of past climate are interpreted in the light of
climate model simulations, and simulations may be constrained by proxy records or
reconstructions based on them. The results of this work are likely to have consid-
erable implications for the understanding of future climate changes; in particular,
the consequences of anthropogenic climate change for regional climatic phenomena
such as drought.
11.7 The Current State of Play
It is clear that dendroclimatology has made major and unique contributions on all
three fronts mentioned: the spectrum of climate variability, hemispheric mean tem-
perature over recent centuries and millennia, and the relationships between global or
hemispheric features, circulation patterns, and regional to local climate variability
and change. As a result, a new paradigm of climate variability and change in recent
centuries and millennia is emerging, which is distinct in a number of respects from
the paleoclimatology of longer timescales and more dramatic shifts in the bound-
ary conditions of the climate system. It is a paradigm in which the spatial and
temporal specificity of high-resolution archives such as tree rings permit a seam-
less approach to the linking of the effects of radiative forcing at global scale with
regional and local climate patterns combining forced and natural internal variabil-
ity (Hughes and Ammann 2009 ) . On the one hand, reconstructions of decadal to
multicentennial changes at hemispheric or global scales provide a test for models of
radiatively forced climate variability and change, whereas spatiotemporal patterns
at these and shorter timescales and smaller, regional spatial scales represent the
combined effects of forced and internal variability. Such regional reconstructions,
however, also constitute a rich resource from which it is possible 'to isolate system-
atic regional climate responses to repeated forcing events' (Hughes and Ammann,
2009 ) ; for example, climatically effective volcanic eruptions. Such analyses have
the potential to contribute to the untangling of the effects of forced and unforced
climate variability at regional scales. The approach is increasingly integrated into
climate science, contributing otherwise unavailable insights, and in turn benefiting
from new challenges.
These contributions, and the many other achievements discussed in this volume,
have been possible because of decades of conceptual and technical development,