IPCC: why the difference between summary for policy makers and WG body of report about extreme weather.?

There is no such single statement/evaluation. Here is the relevant paragraph from the Summary for Ploicymakers.

“Changes in many extreme weather and climate events have been observed since about 1950 (see Table SPM.1 for details). It is very likely that the number of cold days and nights has decreased and the number of warm days and nights has increased on the global scale6 . It is likely that the frequency of heat waves has increased in large parts of Europe, Asia and Australia. There are likely more land regions where the number of heavy precipitation events has increased than where it has decreased. The frequency or intensity of heavy precipitation events has likely increased in North America and Europe. In other continents, confidence in changes in heavy precipitation events is at most medium. {2.6}”

http://www.ipcc.ch/pdf/assessment-report/ar5/wg1/W...

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