Coast-to-Coast Seminar: Anthropogenic Influence on Long Return Period Daily Temperature Extremes at Regional Scales

Speaker: Dr. Francis Zwiers, Director, Pacific Climate Impacts Consortium

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Abstract: There is now a well established approach to detecting and
attributing the causes of observed changes in mean climatic conditions
that has been applied progressively from global scales to regional
scales to temperature and other climate variables. While this research
has provided a great deal of useful information about the causes of
climate change observed during the past century or more, policy makers
and others have also been demanding answers about whether there are
attributable changes in frequency and/or intensity of extreme weather
and climate events. The statistical techniques required to respond to
these questions are only now begin developed. This talk will describe a
standard technique that is used in climate change detection and
attribution research, propose a parallel approach that might be used to
assess whether there is a detectable human influence in the far tails of
the distribution of a climate variable such as daily maximum air
temperature, demonstrate an initial application of the approach, and
discuss limitations and further areas of improvements. Using the
approach that is proposed, we show that an anthropogenic influence is
detectable globally, and in many regions, in the extremes of daily
maximum and minimum temperatures. Globally, waiting times for extreme
annual minimum daily minimum and daily maximum temperatures events that
were expected to recur once every 20 years in the 1960s are now
estimated to exceed 35 and 30 years respectively. . In contrast, waiting
times for circa 1960s 20-year extremes of annual maximum daily minimum
and daily maximum temperatures are estimated to have decreased to less
than 10 and 15 years respectively.

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