539 research outputs found
Impact of externally forced changes on temperature extremes
This thesis investigates changes in temperature extremes between 1950-2005,
analysing gridded data sets of observations and climate model simulations. It
focuses on changes in the frequency of extreme temperatures occurring in single
days or over periods of six or more consecutive days. The study aims to
quantify the significance of changes in extreme temperature events and answer
the following questions. Are external or human-induced forcings together with
natural forcings responsible for the observed change in temperature extremes or
can these changes be explained due to natural climate variability alone? Are the
observed changes consistent with those from climate model simulations? And are
the changes in extremes linked only to changes in the mean climate, or only to
those in climate variability or both? The analysis concentrates on changes from
global to regional scale and from annual mean to seasonal scale. A detection
method is applied to assess if changes are significantly different with respect to
the internal climate variability. Results show that there has been a significant
increase in warm daily extremes and a decrease in cold ones, both on large and
small spatial scales. The increase in warm extremes has been found to be highly
correlated with the increase in mean temperature. The changes in daily extremes
are well represented in climate model simulations. Changes in the persistent
extremes show a detectable increase in the frequency of warm and a decrease in
cold events and are reproducible by models
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