Geoscience Reference
In-Depth Information
Figure 13.1
A schematic of processes driving variability and change in the climate system.
Source: IPCC (2007). Reproduced by permission of the IPCC (ch. 1, Historical overview of climate change science, Report of WG1 1, IPCC,
P. 104, FAQ 1.2, fig. 1).
Climate Change (IPCC), refers to fluctuations
in the mean state and other statistics (such as
the standard deviation, extremes, or shape of
frequency distribution, see Note 1) of climate
elements on all spatial and temporal scales beyond
those of individual weather events. Variability can
be associated with either natural internal processes
within the climate system, or with variations in
natural or anthropogenic climate forcing. Climate
change, by contrast, is viewed by the IPCC as a
statistically significant variation in the mean state
of the climate or in its variability persisting over
an extended period, typically decades or longer.
Climate change may be due to natural internal
processes, natural external forcings, or persistent
anthropogenic-induced changes in atmospheric
composition or land use.
The student may be excused if the distinction
seems fuzzy. Consider
Figure 13.2
. A given climate
record, whether from instrumental or from proxy
sources, may exhibit a suite of behaviors. It may
document a rapid shift from one mean state to
another (B), a gradual trend, followed by a new
mean state (C) or a change in the variance with no
change in the mean over the period of record (D).
Even within a fairly stable mean state, there can be
fluctuations about that state that are quasi-
periodic (B) or non-periodic (C). In turn, a record
might be characterized only by long periodic
oscillation (A). Given that climate variability as
viewed by the IPCC includes fluctuations on all
spatial and temporal scales beyond synoptic
weather events, one could legitimately view all
of the behaviors in the figure as expressions of
