Thursday, 11 October 2018

IPCC: "Extreme weather events" will likely be, in a phrase, less extreme.


While the media this week has been trumpeting the IPCC's headline claim that there is only "ten years left"to save the planet from global warming (note that there is always ten years left to save the planet), they've all but ignored the much quieter recognition by the IPCC that "extreme weather events" will likely be, in a phrase, less extreme.

Roger Pielke Jr. was one of the few to dig through the report to sort the hyperbole from the data, posting on Twitter "a short thread on what the new IPPC report says about trends in extreme events, specifically: on heat waves, drought, floods, tropical cyclones, tornadoes."

Topical stuff, especially in the week of a once-in-a-century hurricane ripping through Florida. So what does the IPCC say we should expect in coming years -- and how likely do they say they know it?

On temperature extremes ...
PIELKE: No change from the IPCC's 2104 Fifth Assessment Report (AR5) or 2011 'Report on Extreme Events' (SREX):
Very likely= fewer cold days and nights
Very likely= more warm days and nights
Likely= "consistent changes are detectable on continental scale in North America, Europe and Australia"
On drought...
PIELKE: No change from AR5:IPCC: "low confidence in the sign of drought trends since 1950 at global scale... likely to be trends in some regions of the world, including increases in drought in the Mediterranean and W Africa & decreases in droughts in central N America & NW Australia"
On floods...
IPCC: "There is low confidence due to limited evidence, however, that anthropogenic climate change has affected the frequency and the magnitude of floods [though some basins see up trends, some down] ...
"In summary, streamflow trends since 1950 are non-statistically significant in most of the world’s largest rivers (high confidence)"
On topical cyclones:
IPCC: "Numerous studies towards and beyond AR5 have reported a decreasing trend
in the global number of tropical cyclones and/or the globally accumulated cyclonic energy... there is only low confidence regarding changes in global tropical cyclone numbers under global warming over the last four decades...
"There is consequently low confidence in the larger number of studies reporting increasing trends in the global number of very intense cyclones."
On tornadoes:
PIELKE: Not mentioned.
Bottom line:
PIELKE: The IPCC once again reports that there is little basis for claiming that drought, floods, hurricanes, tornadoes have increased, much less increased due to greenhouse gases (GHGs). In short, this book is still right:



NB: The original Twitter thread, with all its comments, is here. I've translated from Roger's Twitter shorthand for you. You're welcome.
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