Large progress has been made in the past few years towards quantifying
and understanding climate variability during past centuries. At the same
time, present-day climate has been studied using state-of-the-art data
sets and tools with respect to the physical and chemical mechanisms
governing climate variability. Both the understanding of the past and
the knowledge of the processes are important for assessing and
attributing the anthropogenic effect on present and future climate. The
most important time period in this context is the past approximately 100
years, which comprises large natural variations and extremes (such as
long droughts) as well as anthropogenic influences, most pronounced in
the past few decades. Recent and ongoing research efforts steadily
improve the observational record of the 20th century, while atmospheric
circulation models are used to underpin the mechanisms behind large
climatic variations. Atmospheric chemistry and composition are important
for understanding climate variability and change, and considerable
progress has been made in the past few years in this field. The evolving
integration of these research areas in a more comprehensive analysis of
recent climate variability was reflected in the organisation of a
workshop "Climate variability and extremes in the past 100 years" in
Gwatt near Thun (Switzerland), 24-26 July 2006. The aim of this workshop
was to bring together scientists working on data issues together with
statistical climatologists, modellers, and atmospheric chemists to
discuss gaps in our understanding of climate variability during the past
approximately 100 years.
