The subject of climate feedbacks focuses attention
on global mean surface air temperature (GMST) as
the key metric of climate change. But what does
knowledge of past and future GMST tell us about
the climate of specific regions? In the context of
the ongoing UNFCCC process, this is an important
question for policy-makers as well as for scientists.
The answer depends on many factors, including the
mechanisms causing changes, the timescale of the
changes, and the variables and regions of interest.
This paper provides a review and analysis of the
relationship between changes in GMST and changes
in local climate, first in observational records and then
in a range of climate model simulations, which are
used to interpret the observations. The focus is on
decadal timescales, which are of particular interest
in relation to recent and near-future anthropogenic
climate change. It is shown that GMST primarily
provides information about forced responses, but that
understanding and quantifying internal variability is
essential to projecting climate and climate impacts
on regional-to-local scales. The relationship between
local forced responses and GMST is often linear but
may be nonlinear, and can be greatly complicated by
competition between different forcing factors. Climate
projections are limited not only by uncertainties in
the signal of climate change but also by uncertainties
in the characteristics of real-world internal variability.
Finally, it is shown that the relationship between
GMST and local climate provides a simple approach
to climate change detection, and a useful guide to
attribution studies
