Xtreme Weather and New Math

Bishop Hill links to a Guardian article which in turn links to a paper in Nature by Fischer and Knutti entitled “Anthropogenic Contribution to Global Occurrence of Heavy Precipitation and High-Temperature Extremes.”

Xtreme Weather is back!

They claim that 18% of what they call moderate daily precipitation extremes are attributable to the observed temperature increase since pre-industrial times. (First ‘Huh?’ moderate extremes?) Should temperatures rise by 2C they claim that 40% of predicted precipitation extremes will be caused by human caused temperature increases.

I should think they would be pleased to hear that according to the National Oceanic and Atmospheric Administration’s Global Analysis for 2014, global precipitation was 0.52mm below average in 2014.

No? No. “Likewise, today about 75% of the moderate daily hot extremes over land are attributable to warming.” I could have figured that out without a slide rule. Temperatures have risen–hot spells are more frequent and probably hotter.

They’re very precise. How did they achieve such precision?

“Although the framework is effective, the underlying model experiments often have to be designed specifically for certain events.”

Ah.

Wait. Doing a model run is an experiment?

Wait a bit more. “We base our estimates on well-defined estimates of daily temperature and precipitation derived from long pre-industrial control runs of 25 CMIP5 models.”

Hmm. That would be these CMIP5 models that have done such an excellent job of forecasting temperatures, then:

CMIP5-73-models-vs-obs-20N-20S-MT-5-yr-means1

And what’s this I read further along in the paper?

“Quantifying a human contribution to the likelihood of a single event is challenging because there is sometimes a considerable observational uncertainty in the exact intensity of the event… However, in some cases models may even be unable to simulate the extent of an observed event, which implies that bias correction of mean and possibly even higher-order are required.”

Ya know, I think I’ll wait for a paper based on observations, if you don’t mind terribly.

3 responses to “Xtreme Weather and New Math

  1. I have no problem with describing such model runs as “experiments” — as long as one is clear that the experiments can only yield information on the (unknown) behavior of the models. It’s interpreting the results as reflecting the behavior of the Earth that’s the problem.

  2. If the climate obsessed actually had evidence to offer to support their position, they would offer it.Instead it is about selling, marketing, silencing skeptics, name calling, model runs, massaging history, suppressing critiques, ignoring critics, etc.

  3. That paper really didn’t say anything useful. Of course, if temperatures rise, you are more likely to see temperatures that are above a certain level. Presumably if temperatures go up, the definition of heat wave should change as well.

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