TOBS Adjustment Is Garbage

The USHCN Time Of Observation BIAS (TOBS) adjustment is based on the idea that thermometers reset in the afternoon tend to double count hot days and thus produce a warm bias. For example, Warrenton, MO reset their thermometer at 5PM from 1923 to 1976, so NOAA deducted about 1.5 degrees to compensate.


This theory is easy to test by comparing vs. a nearby morning station. According to theory, the morning station should be cooler. Farmington, MO is close to Warrenton and reset their thermometer at 7 AM from 1931 to 1950, so they should be cooler than Warrenton during that period.


The theory doesn’t work. Farmington summer maximum temperatures (red below) are nearly identical to Warrenton temperatures (blue below.) Only exception is 1935, which is missing data at Warrenton.


 Likewise, the number of hot afternoons is nearly identical at the two stations – again Farmington in red and Warrenton in blue. If double counting was occurring, Warrenton would have more hot afternoons than Farmington during the 1930’s – but it doesn’t.


TOBS theory simply does not work in practice.

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15 Responses to TOBS Adjustment Is Garbage

  1. AndyG55 says:

    ” TOBS theory simply does not work in practice.”

    Yes it does, TH,…

    It does EXACTLY what it was designed to do…

    … that being to help create warming trends where none exist.

  2. Who’s ever heard of a heat wave lasting only one day?

  3. Steve Case says:

    Don’t modern records have continuous records? And didn’t our host do one of those studies a while back to show that the TOBS effect isn’t what it’s claimed to be? I’ve played around with random variations and determined that the best times to take readings are right after breakfast or just before bed time.

    Doesn’t the 7:00 AM station also introduce a bias, and did NOAA adjust for that too? I get the distinct feeling they make adjustments one way only.

    • JP says:

      The entire TOB is a crock. And yes, it would be nice if the reporting stations sent 24×7 data. Instead we get a daily Tmax and Tmin. NOAA knows what it’s doing

  4. TimG says:

    You miss the point: TOBS is used because when temperature changes a lot from one day to the next the higher of the two is recorded twice. The seasonal averages are irrelevant – it is the day to day changes that introduce the bias.

    BTW: I think the surface measurements are junk and can’t be trusted. I am only saying your argument on this particular point is wrong.

  5. Andy DC says:

    If a station is 105 at 5 pm on a certain day and is 83 at 5 pm the next day, it is hard to believe that anyone would count the high temperature for the next day as 105. It makes no sense at all.

    • -B- says:

      It would only be an issue when the following day’s high was lower than the max temperature from 5pm to midnight. This does happen from time to time but any human would realize this and correct for it by resetting the thermometer again in the morning. And even if they didn’t TOBs could be corrected for by looking at the difference between the two days at a nearby station and comparing to the suspect station. Or do the many different checks to see if TOBs even needs a correction by comparing stations in many different ways. The error due to TOBs should be random and should cancel out in a large data set. (it would also have an effect with lows on winter nights when it warmed) From everything Tony has done, TOBs apparently just drops out as expected.

      • tonyheller says:

        Exactly. Anyone with an IQ over 30 will reset the maximum in the morning and the minimum in the afternoon. I figured this out in about two days when I was seven years old.

        • The data would auto-correct anyway. One heat wave lasts 5 days and ends at midnight. The next heat wave lasts 7 days and ends at noon. They all come in chaotically and the average works out to be same no matter what time you reset.

  6. JamesG says:

    Thanks for this. I long had a gut feeling TOBS was nonsense despite a lot of sceptics being talked around on this issue but you just can’t argue against actual data.

  7. Shawn says:

    Tony, have you recieved any comment from the likes of Judith Curry, or Anthony Watts regarding this presntation? It looks pretty damning, especially when you consider that these adjustments are being implemented automatically in software.

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