Apocalyptic Heat Predictions for Los Angeles Raise Serious Questions

In the Los Angeles Daily News a couple weeks ago, Susan Abram reported on the release of two new climate change reports from the Los Angeles County Department of Public Health. The situation provides a textbook example of problematic journalism and science.

In Abram's story, she states that the reports predict "some places, such as Sylmar and Woodland Hills, for example, may see up to 25 straight days of 95 degree or hotter temperatures." No, that is not what the reports say.

The L.A. County DOPH report states that "in Sylmar, climate change is predicted to triple the number of heat days (when temperatures are over 95 F) from nearly seven days a year now to more than 25 days per year in 2050," and shows the following chart.

Abram erroneously reports that the prediction is for "up to 25 straight days of 95 degree or hotter temperatures," whereas the prediction is for up to 25 days per year -- regardless of when they occur. Big difference here in terms of impacts on public health, water supply, etc., between these two options. The former is clearly far worse than the latter, but it is only the latter that is being predicted.

I note that when the media makes errors on reporting climate change issues, it always seems to be a systematic bias in favor of the error being on the exaggeration side of impacts, rather than underestimating the projected problem. If errors were randomly distributed, we would expect to find them approximately equally spread between under- and over-stating the concerns.

Also note that Woodland Hills is predicted to have less than 17 days per year greater than 95 F by mid-century, not in the "up to 25" range if we want to get picky. Only Sylmar and Porter Ranch are projected to have up to 25 extremely hot days per year by 2050.

So the predicted problem has been overstated in the media from a couple angles. When we look at the actual climate trends in and around Los Angeles, it appears the problem itself may be grossly overstated as well.

NOAA's National Weather Service database has the following four long-term sub-regions in the L.A. area: Long Beach, L.A. downtown, L.A. airport, and Santa Maria. As well, there are a suite of other local stations with varying degrees of data quality (many have very incomplete climate records, precluding any trend analyses). But looking at the trends in numbers of days above 95 F for the four primary regional stations, as well as the other local stations with good quality data, reveals no evidence whatsoever that the number of hot days in the L.A. area has generally increased since 1970, or over the last 30 years.

In fact, the evidence is overwhelming for a significant declining -- not increasing -- trend in the number of days per year above 95 F, both over the last 45 years and the last 30 years. This is consistent with the  general cooling trend for the L.A. region over these periods.

I'm not even sure where the data for the "current" number of days above 95 F from the L.A. County DOPH report came from. For "Downtown LA," the DOPH report shows only 1.4 days per year at present exceeding 95 F. This appears to be very wrong. The NOAA-NWS database provides an average of 7 days each year with maximum temperatures above this threshold for downtown L.A. since 1970, and an average of 6.5 since 1984.

Same with Studio City, which is right next door to Burbank-Glendale. The L.A. County DOPH report states that Studio City currently has only 2.3 extremely hot days each year, whereas the NOAA-NWS database has Burbank -- just six miles away and at almost the same elevation -- at 18. Same discrepancy applies for Sylmar, which is just 13 miles northwest of Burbank.

The findings and figures in the DOPH report come from a study done by UCLA, but a look at this study doesn't provide the necessary answers, either. Why are current numbers of extremely hot days in the UCLA/DOPH reports for some areas of L.A. so low, and why do the expected numbers of hot days in the near future deviate so much from the trends observed over the past half-century? Certainly, any public communications regarding these climate modeling predictions should be emphasizing that they are moving in a completely different direction than recent multi-decadal trends.

There are a lot of unresolved questions about these reports, and residents of L.A. should be trying to figure out exactly what their current climate is and where it is headed, because the data I see appears to tell a much different story than the UCLA and DOPH reporting does.

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