Chester County PA - Analytical Battle of Actual vs. Altered Climate Data

[Mike Cycle]

Paul, I don't know if you saw this, but the detected breaks for Coatesville line up very well with documented results.  I made a figure, attached.  HOMR has errors, you must refer to the 530-1, and even that has an error in Gordon's address which was resolved by looking at property records.  You will also need to read through every monthly report to catch changes in coords or observation times--I did.  Somewhere in ~1928 Gordon notes that he was ill and used chart recorder for a while--I ignored that.   If you don't supply all of this information to Claude, you will not get a useful result.

Don't expect the breakpoints to coincide exactly.  It may take a month or more for the break to be visible to the math.  

If you look at the map--its 100% clear and obvious that 1 SW moved from a hot location to progressively cooler ones.  It also clear you have not provided this information to the AI. 

[Mike Cycle]

I asked Gemini these three questions, italicized for clarity. You could ask any AI the same set of questions, and get the same general answers.

Q:  For collecting good-quality long term climate temperature data, 100 years+, describe a hypothetical location in a temperate climate. Short answer.

A: A ideal hypothetical location in a temperate climate for a 100-year climate station is an isolated, protected rural valley plateau.

Q:  If you took the station just described, and after 100 years of data, moved it into an urban area, what would happen? Short answer. Describe the reverse case as well, where the station begins in an urban area.

A: Moving a Rural Station to an Urban Area: Moving a 100-year rural station into a city causes an artificial temperature spike.

A: The Reverse: Moving an Urban Station to a Rural Area:  Moving a station from a city out to a rural area causes an artificial temperature drop.

Q: How would you correct for the station move?

A:  To correct for a station move, climate scientists use a statistical process called homogenization.

Here is how the correction works:

• Create a Reference Record: Scientists select a group of nearby, undisturbed "neighboring" stations that experienced the same regional weather but did not move.
• Identify the Breakpoint: They calculate the average temperature difference between the target station and the neighbor group. A sudden, permanent shift in this difference confirms the exact date of the move.
• Calculate the Offset: Scientists compare the data from a window of years immediately before the move to a window of years after the move against the stable neighbors to determine the exact bias (e.g., the city move made it 1.2°C warmer).
• Adjust the Historical Data: They apply that 1.2°C offset to the entire block of data prior to the move, lifting (or lowering) the old record so it seamlessly aligns with the new location's environment.

 

[ChescoWx]

On 8/11/2026 at 1:56 PM, Mike Cycle said:

Paul, I don't know if you saw this, but the detected breaks for Coatesville line up very well with documented results.  I made a figure, attached.  HOMR has errors, you must refer to the 530-1, and even that has an error in Gordon's address which was resolved by looking at property records.  You will also need to read through every monthly report to catch changes in coords or observation times--I did.  Somewhere in ~1928 Gordon notes that he was ill and used chart recorder for a while--I ignored that.   If you don't supply all of this information to Claude, you will not get a useful result.

Don't expect the breakpoints to coincide exactly.  It may take a month or more for the break to be visible to the math.  

If you look at the map--its 100% clear and obvious that 1 SW moved from a hot location to progressively cooler ones.  It also clear you have not provided this information to the AI. 

 

 

Hi Mike I did of course supply all of the above information to Claude to ensure we got a useful result! As you know homogenization remains nothing more then a hypothesis-driven statistical correction, it is of course not a measurement. Pairwise algorithms like PHA infer breakpoints from neighbor differences, and when 44 of 51 Berkeley breakpoints at Chesco stations are a code 4 meaning empirically detected, with absolutely no metadata backing, that's an algorithm asserting station changes that are clearly not able to be documented. That is a legitimate target for scrutiny, it is not fringe skepticism. My finding that the adjustment series itself carries a significant linear time trend (r² 0.34–0.67) is the greatest point I have — a correction for discrete, random station artifacts shouldn't behave like a smooth ramp as these adjustments do! 

[ChescoWx]

You will often here folks say well while our average daytime highs may not be warming significantly....we are certain that the nightime lows are warmingg....Well I went back and did a statistical analysis to see if between 1890 and 2025 we saw statistically warming of overnight lows and daytime highs along with the overall average temperatures. We used both a pure raw all station mean which is just the raw untouched data and an anomaly composite which while still raw data, treats each individual station referenced to its own baseline so the changing station roster and locations can't fabricate some false trend.

Raw all-station mean (the literal, unadjusted county average): none of the three are statistically significant.

• Average high: +0.055 °F/decade, p = 0.073 — warming, but just short of significance (borderline).

• Average low: +0.022 °F/decade, p = 0.49 — not significant.

• Overall average: +0.039 °F/decade, p = 0.15 — not significant.

So by the pure raw mean, there's no statistically significant warming or cooling in any of the three over 1890–2025 — a slight (non-significant) warming lean in all three.

 

Anomaly composite (still raw data, but each station referenced to its own baseline so the changing station roster can't fabricate a trend): two of the three are significant, and they point in opposite directions.

• Average high: +0.094 °F/decade, p = 0.003 — significant warming.

• Average low: −0.075 °F/decade, p = 0.008 — significant cooling.

• Overall average: +0.010 °F/decade, p = 0.72 — not significant (the high and low cancel out).

The one thing both methods agree on firmly: the overall average temperature shows no statistically significant trend either way across the 135 years across Chester County from 1890-2025. Below are some charts that highlight all of the above.

[Mike Cycle]

What smooth ramp do you refer to? I just glanced at the breakpoints at BEST for the stations in the table and none of them look like "smooth ramps".  

Coatesville's breakpoint are fully documented at this point.  I have shown you that there is hard documented real world events driving the breakpoints for this station.  If you think there is something off about the breakpoints for the other stations, and that the published work of scientists around the world is flawed,  then it is on you to do the deep dive on the histories through all available sources and make your case.  Don't just wave your hands saying "absolutely no metadata backing, that's an algorithm asserting station changes that are clearly not able to be documented"--without first scouring all source for that documentation.  

For West Chester, I just took a quick look at the breakpoints at BEST, the 530-1, and HOMR records.  About half the breaks are clear just from the 530-1 and HOMR.  There are breakpoints at ~1978, ~1982 and ~1988 that don't have explanations yet and may be in the paper forms, or other records. Its the Daily Local--there are going to be a lot of records about where they were located. Have AI write a tool to download all the paper forms from batch "AA92589" or just do it manually around those dates.  Anyway, it is on you to prove there is no documentation for these moves, you cant just say there aren't any without looking at the available documentation first.

 

[ChescoWx]

1 hour ago, Mike Cycle said:

What smooth ramp do you refer to? I just glanced at the breakpoints at BEST for the stations in the table and none of them look like "smooth ramps".  

Coatesville's breakpoint are fully documented at this point.  I have shown you that there is hard documented real world events driving the breakpoints for this station.  If you think there is something off about the breakpoints for the other stations, and that the published work of scientists around the world is flawed,  then it is on you to do the deep dive on the histories through all available sources and make your case.  Don't just wave your hands saying "absolutely no metadata backing, that's an algorithm asserting station changes that are clearly not able to be documented"--without first scouring all source for that documentation.  

For West Chester, I just took a quick look at the breakpoints at BEST, the 530-1, and HOMR records.  About half the breaks are clear just from the 530-1 and HOMR.  There are breakpoints at ~1978, ~1982 and ~1988 that don't have explanations yet and may be in the paper forms, or other records. Its the Daily Local--there are going to be a lot of records about where they were located. Have AI write a tool to download all the paper forms from batch "AA92589" or just do it manually around those dates.  Anyway, it is on you to prove there is no documentation for these moves, you cant just say there aren't any without looking at the available documentation first.

 

 

 

 

No hand waving Mike....just no clear documented reasons as only four of 51 (8%) trace to a documented real physical cause — three moves and only one TOB change. There are 2 zero break stations that are our controls - Coatesville 2W and Hopewell demonstrate that the PHA is indeed selective as it left these 2 stations untouched: NCEI applied no adjustment to either - which proves the 14 breakpoints at Coatesville 1SW were a deliberate finding rather than a default. The Coatesville 1SW dates, all code 4: 1896-12, 1902-02, 1917-08, 1920-09, 1922-08, 1930-10, 1936-05, 1941-06, 1946-04, 1959-11, 1968-05, 1971-04, 1973-07, 1976-02. Fourteen inferred discontinuities against six documented HOMR relocations, coinciding with none of them. 

The linear ramp clearly fits far better than any step. And when you allow both, the step collapses to −0.050 °C while the slope survives essentially intact at +0.182 °C/dec. A one-time convention change explains basically none of it. And more importantly the actual magnitude is out of range. The Coatesville adjustment swings +1.51 °C from first decade to last (West Chester, from NCEI's own file, swings +2.38 °C). Published TOB corrections for a full afternoon-to-morning switch run roughly 0.2–0.5 °C in annual mean. So TOB, even granting it entirely (which is not valid), accounts for perhaps a third of the Coatesville adjustment and a fifth of West Chester's.

To summarize how it all fits together Mike:

1. Raw agreement across stations. Coatesville 1SW −0.366, West Chester 2NW −0.409, Phoenixville 1E −0.339 over 1941–75, all p ≤ 0.0012, inside each other's error bars.
2. Both systems erase it. Berkeley and NCEI each render all three non-significant, with adjustment trends correlating at r = 0.9986.
3. The correction is a "smooth ramp" which you question above but certainly not a step — which no single documented event can explain.
4. Its size exceeds TOB by 3–5×.
5. The breakpoints lack documentation. Fourteen at Coatesville, all code 4, against six documented relocations in HOMR. At West Chester, April 1921 and November/December 1927 are documented observer-and-site changes classified as empirically detected, and the March 1936 relocation produced no breakpoint at all.
6. Phoenixville is the cleanest case — no detected convention change anywhere in its record, and it still cools at −0.339 (p=0.0012) - why is that? So many questions and still so few answers!!

The unanswered questions that follows from this is narrow and should be answerable: exactly what documentation supports the fourteen breakpoints at USC00361589 - Coatesville 1SW and what portion of the adjustment at Coatesville is attributed to time-of-observation versus other causes? That last question is the one they can't deflect — because the shape of their own adjustment says it isn't mostly TOB because if TOB was factored in it would actually be supporting a warming not a cooling adjustment at Coatesville! 

[chubbs]

13 hours ago, ChescoWx said:

 As you know homogenization remains nothing more then a hypothesis-driven statistical correction, it is of course not a measurement.

Nope.  Homogenization is accepted science. Thoroughly tested over decades. Proven to obtain the correct climate information from raw temperature when station changes have occurred. The raw temperature data in Chester County is contaminated by myriad station moves and changes. Assuming that Coatesville and other Chesco COOPs stayed in exactly the same spot with zero equipment and method changes over decades will give you the wrong climate answer every time.

The cooling of Coatesville between 1945 and 1949 is well documented in this thread. The regional raw temperature data is 100% conclusive on this point. Coatesville was much cooler in 1949 than it was in 1945 relative to all stable regional stations. Comparison of Coatesville to Phoenixville over the period 1941-75, is immaterial; because, as the bottom chart shows, Phoenixville had a station break in 1948. The post-war  Phoenixville and Coatesville station breaks occurred at different times proving that they are not weather-related.

Mike's analysis and the NCEI bias adjustments are completely independent, derived from 2 different sources of information. Mike uses the station records. Bias adjustments use raw temperature data. The fact that they agree so well shows how powerful and accurate homogenization is in Chester County.

Your AI slop is wasting our time if it doesn't focus on the station breaks themselves. Regression over 35 years is not the right tool to identify station breaks. You need much more focused analyses to look at station breaks. The 1945-49 period for the Coatesville post-war move/changes for instance. 

[ncjoaquin]

Sometimes I think my life is not always that exciting.  Then I come here to see that this weird ass discussion is still going on after more than 2 years.

[Mike Cycle]

Paul, you have made many claims in the last few comments.  These look like strawmen to me, and I have summarized them below.  To me, it appears you are making these comments to show that the accepted process of dealing with raw noisy data is flawed, and therefore that published climate trends are based on a flawed process.  

• "86% of breakpoints are undocumented" → implies the algorithm should mostly find documented breaks. It's designed to catch undocumented ones — a high rate is expected, not damning.
• "Chester County's raw data shows no significant county-wide trend, so warming is manufactured by adjustment" → implies mainstream science predicts a clean, significant trend in every small local raw sample. Nobody claims that — a handful of stations in one county is noisy by nature, which is the whole reason homogenization exists.
• "The correction is a smooth ramp, not a step, so no single event explains it" → implies a legitimate correction must be one discrete jump. Many small breaks stacked over decades naturally produce a ramp-shaped cumulative correction.
• "Some stations (Coatesville 2W, Hopewell) got zero adjustment, proving selectivity" → implies adjustments should be applied roughly evenly everywhere. A detector that only flags real breaks and leaves clean stations alone is working correctly, not cherry-picking.
• "Highs are warming while lows are cooling — that's a contradiction" → implies day/night trends must move together. Diurnal-range divergence is a documented, separately-studied climate phenomenon, not a paradox.

Yet, the Chester County raw data is in good agreement with published climate trends, more so when the urban makeup of the pre-1940 station group is taken into account.  

I suggest looking into the West Chester 2 NW records to document the rest of the breakpoint.

 

[ChescoWx]

Mike, this is in my view the most useful thing anyone has put in this thread, and it changes my position on several points. Thank you for doing the archival work rather than just asserting it.

Taking your points in order. You're right that "undocumented" in the algorithm's metadata linkage is not the same as "no documentation exists." I was treating the two as equivalent and that was a wee bit sloppy. Your figure shows some actual events behind most of the Coatesville breaks, and the burden argument is fair — I shouldn't claim an absence of records without going through the 530-1s, the deeds and the aerials first. I hadn't. You had - thanks!.

You're also right that a high rate of undocumented detections is expected from a detector built to catch undocumented changes, so the 86% figure doesn't carry the weight I was giving it. I'd already dropped that argument after NCEI sent me their changepoint list for this station — it shows 4 of 12 linked to documented events, not zero, so the Berkeley code counts were never a good proxy for what the PHA is doing.

On the ramp point: Mike - you're right - many small stacked breaks produce a ramp-shaped cumulative. I proved your point without meaning to — cumulating NCEI's twelve discrete changepoints gives a series that fits a straight line at r-squared 0.495. That's a stack of steps looking smooth, exactly as you say. Zero-adjustment stations and the diurnal range point are both fair points also. A detector leaving clean stations alone is working, and DTR divergence is a studied phenomenon rather than a contradiction. And I accept that a handful of stations in one county is a noisy sample by nature.

Now a couple things I will push back on a little, not on it's substance but on how firmly you state it. Your own figure marks 1920 unresolved. And I'd read the 1959-1976 group differently to the header on it. The box says five breaks, but NOAA only has two in that window — 1959 and 1971. The other three are BEST-only. And BEST's five nearly cancel: -0.50, +0.37, +0.02, +0.72, -0.71 comes to -0.10 F net across seventeen years, which isn't doing much work. NOAA's two come to +0.40 F, and that's the direction you'd correct for spurious cooling, not for a station warming under encroaching infrastructure.

Which brings me to the part I can't pull together. The station moves to progressively cooler sites implies the raw acquires spurious cooling and needs the later data warmed — which matches what NOAA applied. Infrastructure growing up around the site implies the opposite. Both are in your account of this window. Which one do you think is actually driving it?

For what it's worth, your 1959 and 1971 values match NCEI's changepoint list for this station exactly once converted — -0.54 and +0.94 F against -0.28 and +0.53 C. So we're working from the same PHA output, which is worth knowing! Thanks again Mike!!

That window also stops something I was about to post. I ran a segmented breakpoint analysis on the raw daily data and it attributed only one concordant discontinuity to Coatesville, January 1973. I then fitted the 1952-82 trend with that single step in the model. If there are more real breaks in that window, my model is under-specified and the number isn't worth quoting. I'm going to refit it against the full break set before I use it. If it doesn't survive, I'll say so here. Stay tuned for that later!

The one thing still open is narrower and comes out of NCEI's own files rather than the station history. Cumulating their twelve changepoints reproduces +0.123 C/decade of adjustment trend. The actual adjusted-minus-unadjusted trend for the same station and years is +0.184. About a third isn't in any listed changepoint. It isn't rounding, and it isn't run-to-run variation — I compared two pulls of the adjusted series two days apart and they were identical across all 119 years at West Chester. I've asked NCEI what accounts for it rather than guessing, and I'll post their answer either way. I sent the email this morning to my contact there...stay tuned for more of that later!

Now my ask - would you be willing to share your compiled 530-1 and deed work for Coatesville, and whatever you have for West Chester? I'd rather build on it than duplicate it badly, and I'll take your point about the 1978, 1982 and 1988 West Chester breaks — the Daily Local should have left a trail worth chasing.

Charlie, I think most of the above answers you as well. You were right that a 35-year regression is not a breakpoint test, and running it properly is what led here. On 1945-49 specifically, NCEI's list has a documented move at 1946-01 with a +0.79 C step, so something documented did happen there. I still can't test that window myself — only three Chester County stations cover 1930-1975 with continuity and attribution needs four — so at this point we can't claim it either way.

Paul

[Mike Cycle]

The main question of this thread is whether the adjustments to raw data are a) valid and b) essential.  The deep dive on Coatesville upthread answered these two questions for Coatesville with two resounding YESs for that station. 

Here is the breakpoint analysis for Phoenixville 1E.  It also demonstrates that the adjustments done to the raw data are a) valid and b) absolutely necessary.  Note that all of the aerials from 1927 forward show changes at the site--roughly every ten years between aerials--so there is going to be microsite changes. 

One has to wonder, for all of the time some folks have put into explaining why the adjustments are arbitrary, ad hoc, suspect, etc etc, why they did not just take two hours and look at the easily available documentation on line. 

 

[ChescoWx]

Not so fast Mike!! We are not close yet to what think is being answered! The deep dive above clearly has not yet answer these two questions for Coatesville! First the refit I promised with some very important findings!! and then where I think you and I are answering different questions. At the end I will address your Phoenixville box above.

I said I wouldn't quote that 1952-82 trend until I'd refit it against the full break set, because if there are several real discontinuities in the window then a single-step model is under-specified and the number is worthless. I've now done it, and the result is quite surprising!! The mechanism first, because it's the interesting part. A step term and a trend term compete for the same variance in a regression. If Coatesville's apparent cooling were really just the station stepping down at a few dates, fitting those steps should soak up the drop and leave the residual slope flattened toward zero. That is exactly the test. But what actually happened is the complete reverse. Every fitted step comes out positive - the model wants the later years lifted, not lowered - and lifting the later years forces the underlying line to fall more steeply to still pass through the data. Coatesville 1952-1982, annual, trend and steps estimated jointly in one model rather than subtracting steps first:

  no steps                              -0.594 F/decade   p = 0.0001
  1973 only (my attributed break)       -0.735 F/decade   p = 0.0048
  NOAA's two (1959, 1971)               -0.959 F/decade   p = 0.0272
  Berkeley's five (1959/68/71/73/76)    -1.657 F/decade   p = 0.0188

Significant in all four. Fitted steps +0.45, +0.46, +0.89, +0.91, +0.81 F, every one positive. So the more of your documented breaks I grant, the more raw cooling is left over needing some other explanation.

The weaknesses, because I'd rather flag them myself. Not one of those steps is individually significant - best p is 0.17, standard errors 0.6 to 0.7 F against steps of 0.45 to 0.91. So this isn't proof the steps are positive. It's that the data, asked where steps would sit if they exist, puts them in the direction that deepens the cooling. Suggestive, not conclusive, and it neither confirms nor refutes your documentation, because at annual resolution this series can't resolve steps that size. AIC prefers the no-steps model over every step set, though with those SEs that's weak too. And the five-break fit is badly under-powered: seven parameters on 31 values at 0.75 F residual SD detects a genuinely present trend only about 14% of the time in simulation. It found one anyway, which is why I'm reporting it rather than quietly setting it aside - it's the most favourable number to me and the one I trust least.

So what I'll stand behind is a range: -0.59 to -1.66 F/decade over 1952-1982 depending on the break set assumed, significant in all four specifications.

Now, on validity and necessity. I think we're answering different questions.

Your work establishes that events occurred at those dates, and I've conceded that without reservation. Validity is a further step: it requires the magnitude applied at each date to be right. The PHA sizes each step from neighbour comparison, not from the site. A 0.3 mile move is a documented fact. The +0.86 C attached to it is an estimate. Nothing in the 530-1s, the deeds or the aerials tests that estimate, and that's the question I keep coming back to - it isn't answered by more documentation, however good the documentation is.

Necessity is different again. If the raw cooling at Coatesville were an artifact of the station changes, fitting those changes should dissolve it. It doesn't. It deepens it!!!!. Whatever else that shows, it isn't what "the adjustment is essential to get the right answer" predicts.

And about a third of Coatesville's adjustment trend isn't attached to any listed changepoint at all. NCEI's twelve cumulate to +0.123 C/decade against an actual adjusted-minus-raw trend of +0.184. Station history can't validate a component that no documented event is claimed to explain. I've asked NCEI what accounts for it rather than guessing, and I'll post their answer either way.

On Phoenixville I'd want to look at your figure properly before saying much, and I'll say up front that my own analysis can't support a claim about that station in either direction. When I tested its 1952-82 trend against a step placed at every possible date, 14 of 21 rendered it non-significant. That series is too short and too noisy to separate a step from a trend, so I'm not going to argue it either way. I'd also note that if the microsite is changing continuously - your reading of the aerials is roughly every ten years from 1927 forward - then the disturbance is gradual, and a step function is an odd model for gradual drift.

On the two hours: fair enough, and I've said as much. Though the changepoint list I've been working from came from NCEI directly on request, and isn't online anywhere.

The offer stands on your 530-1 and deed compilation. Your dates are better than the ones I read off your figure, and the magnitude question needs them.                                        

Now regarding the last Phoenixville block - that block does not say what your post said. Your comment claims the adjustments are "valid and absolutely necessary," but the header states ten breaks now carry a documented physical cause and seven smaller breaks remain unexplained, plus one marked UNRESOLVED at 1966 and a merged box labelled "UNDOCUMENTED — 7 BREAKS." That's 10 of 18, not a resounding yes!!!! Thanks for posting it — it's a more careful figure than the summary suggests.

What strikes me most is that the two sources diverge here in a way they don't at Coatesville. At 1940 — the largest documented move in the record, 2.1 miles — BEST flags +0.75 F and NOAA flags nothing at all. At 1942 it's the reverse. At 1985 you note the NOAA break is a single-station calibration artifact. If two implementations of neighbour-based detection disagree about whether the biggest documented move in the record produced a break, that seems worth more attention than either of us has given it.

The 1920 entry is the strongest piece of documentary work in either of your figures, incidentally — coords changing then reverting a year later while the offset doesn't is a real finding and I'd not have got there.

My own analysis cannot support the claim that Phoenixville cools — which matters because Phoenixville has been used as a comparator throughout this thread. Charlie dismissed my Coatesville–Phoenixville comparison over a 1948 break, and I cited Phoenixville's raw trend earlier in the exchange. Testing its 1952-82 trend against a step at every possible date, 14 of 21 rendered it non-significant. Too short and too noisy to separate a step from a trend, so to date we cannot find total support for these NCEI adjustments to Coatesville 1SW 

Paul

[ChescoWx]

What remains genuinely open regarding Coatesville 1SW remains  the magnitudes have never been independently checked. A documented 0.3-mile move does not actually tell us the offset should be +0.86 °C. That number comes from neighbor comparison, not from the site. Nobody in this thread has tested whether the applied steps match what the physical changes would produce. Also of note about a third of the adjustment trend attaches to no listed changepoint at all. +0.123 reconstructed against +0.184 actual. No station history can validate a component that no documented event is claimed to explain, and NCEI hasn't yet answered that from my earlier email. Lastly, and what can't be overlooked is that the raw cooling doesn't behave the way the artifact explanation predicts. Fitting the breaks actually deepens it rather than dissolving it!!