NCAR paper on record high temperatures an artifact of putting thermometers in urbanized areas

“A new paper that is soon to appear in the journal Geophysical Research Letters finds that across the U.S. daily record high temperatures are being set at about twice the frequency of daily record low temperatures and that this ratio—number of record highs to the number of record lows, has been growing larger over the past 50 years.

The popular press seems to be particularly taken with this finding, although headline proclamations fail to disclose important details of the actual findings reported by the National Center for Atmospheric Research’s (NCAR) Gerald Meehl and colleagues.

Although you can hardly blame the press, because the NCAR press release did much to lead them down this muddy path.

Meehl et al. find that the reason more daily maximum temperature records are being set than daily minimum temperatures records is because there are fewer than expected daily lows records being set, not because there are more daily high records than expected.

In other words, our days are not becoming extremely hotter, but our nights are becoming less extremely cold. This fact is buried in the press release and consequently in most of the coverage—likely, because this finding has pretty benign, if not beneficial, implications. …

[The process of urbanization] warm[s] nights more than days, … — something which has not been accounted for in the results of Meehl et al. (because it is virtually impossible to do so at a daily level), but something that is widely known to be occurring.

A report just published earlier this week estimates that urbanization and other land use changes are responsible for half of the observed temperature rise in recent decades in the U.S. This is similar to what Ross McKitrick and WCR editor Pat Michaels found for global land-based temperatures in a paper published two years ago. …

[W]hile the observations suggest that our nights are warming faster than our days, this is not so in the NCAR climate model which suggests that the days and nights are warming up at the same rate. Such a model error leads to the model grossly overestimating the frequency and intensity of future heat waves. …

Repeat after us—if the models can’t replicate reality (for the right reasons) they can’t reliably predict the future.

So, the bottom line here is this—climate change in the U.S. during the past 50 years has resulted in fewer extreme nighttime low temperatures, while the daily extreme high temperatures have been little affected. And, at least one leading climate model fails to correctly capture this behavior.

Ask yourself this, is this the impression that you got from the coverage of this in the popular press?” “U.S. record temperatures — a closer look

“[T]he closure of thousands of rural stations and expansion of urban areas into previously rural or suburban areas [has created] enormous “heat sinks,” that prevent night time temperatures from dropping to the extent that they would in a nearby rural setting. Hence more stations reporting greater frequencies of maximum temperatures and fewer minimums.” “A critique of the October 2009 NCAR study regarding recording maximum to minimum ratios

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