Title: Temperature fluctuations in a changing climate: an ensemble-based experimental approach,
Abstract: There is an ongoing debate in the literature about whether the present global
warming is increasing local and global temperature variability. The central
methodological issues of this debate relate to the proper treatment of
normalised temperature anomalies and trends in the studied time series which
may be difficult to separate from time-evolving fluctuations. Some argue that
temperature variability is indeed increasing globally, whereas others conclude
it is decreasing or remains practically unchanged. Meanwhile, a consensus
appears to emerge that local variability in certain regions (e.g. Western
Europe and North America) has indeed been increasing in the past 40 years. Here
we investigate the nature of connections between external forcing and climate
variability conceptually by using a laboratory-scale minimal model of
mid-latitude atmospheric thermal convection subject to continuously decreasing
`equator-to-pole' temperature contrast, mimicking climate change. The analysis
of temperature records from an ensemble of experimental runs (`realisations')
all driven by identical time-dependent external forcing reveals that the
collective variability of the ensemble and that of individual realisations may
be markedly different -- a property to be considered when interpreting climate
records.