Detectable regional changes in the number of warm nights

Analyses gridded observed and multi-model simulated trends in the annual number of warm nights during the second half of the 20th century
Shows that there is evidence that external forcing has significantly increased the number of warm nights, both globally and over many regions
Defines thirteen regions with a high density of observational data over two datasets, comparing observed and simulated trends from 20th century simulations
- The 13 regions include: Southern Australia, Alaska, Western North America, Central North America, Eastern North America, Northern Europe, Mediterranean, Northern Asia, Western Asia, Tibet, Eastern Asia, South-East North America, and Central Europe
The main analysis period is 1951–1999, with a sub-period of 1970–1999
Analyses periods of 1955–2003 and 1974–2003 in order to investigate if observed trends changed past 1999
Both observed and ensemble mean model data from all models analyzed show a positive trend for the regional mean number of warm nights in all regions within this 49 year period (1951–1999)
Finds the trends tend to become more pronounced over the sub-period 1970–1999 and even more so up to 2003
Applies a fingerprint analysis to assess if trends are detectable relative to internal climate variability
Finds that changes in the global scale analysis, and in 9 out of 13 regions, are detectable at the 5% significance level
- The exceptions are Central Europe, Eastern Asia, Western Asia and the Tibetan Regions
States that a large part of the observed global-scale trend in TN90 (an index of observed and modeled annual data) results from the trend in mean temperature, which has been attributed largely to anthropogenic greenhouse gas increase
This suggests that the detected global-scale trends in the number of warm nights are at least partly anthropogenic

Detectable regional changes in the number of warm nights

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