NZT7 uses defective raw data

Albert Park 1902 looking south

The official New Zealand Temperature Record is made up of historical temperature readings (raw data) and NIWA’s adjustments. Both of those components are unreliable.

The 169-page Report on the Review of NIWA’s “Seven-Station” Temperature Series, or the Review Report (RR), published by NIWA in December 2010 devotes very little space to that bane of climatologists — the urban heat island (UHI) effect. It has been long recognised that air temperature readings taken in towns and cities are affected by the heat absorption of concrete and tarseal surfaces; by exhausts of vehicles, aeroplanes and air-conditioners; and by structures which deflect wind and confine humidity.

Because a “heat island” is not representative of the wider region or country, most climatologists try to give them a wide berth. Wikipedia says that “the temperature difference between urban areas and the surrounding suburban or rural areas can be as much as 10°F”.

A similar enemy of the climate archivist is “shelter” — trees or structures which interfere with the thermometer’s normal exposure to wind or sun, and thereby cause distortions.

The mean temperature impacts of both UHI and shelter are typically gradual, but non-linear. They are hard to detect and almost impossible to correct. Most climate archivists simply omit any sites suspected of being contaminated by UHI/shelter.

Albert Park 1902 looking south-east.

Albert Park

Albert Park in Auckland is a prime suspect for contamination by both urban-driven heat and shelter. A glance at NIWA’s table of adjusted warming trends (RR, p 5) shows Auckland at a whopping 1.53°C/century, which is almost double the 0.83°C/century averaged by the other six sites.

The site was officially investigated in 1980 by J.W.D. Hessell, a senior meteorologist with the New Zealand Met Service, and was ‘found guilty’. His peer-reviewed paper, published in a leading journal, noted that:

Visitors to this central park today cannot fail to be impressed by the many large exotic trees, most of which were planted about the turn of the century and some of which, more especially those planted later, are still growing. The instrument enclosure is surrounded on all sides by trees and buildings which shelter the site to a great degree. Sheltering was much less in the years preceding 1940. This fact has been commented on by Finkelstein — who pointed out that in no year since 1930 has the annual wind achieved the mean of those before.

The author went on to consider “urbanisation” as a separate issue:

The urban area population of Auckland increased by 60% between 1936 and 1966, this percentage giving an index of urbanisation there. Quantitative assessments of sheltering and of urban “heat island” effects cannot be satisfactorily resolved unless either or both can be shown to be negligible. The Albert Park data have been treated as comprising two separate periods, 1910–40 and 1941–67 which are compared. The indications are that sheltering and urbanisation have contributed to the apparent temperature increase.

When Salinger was preparing the 7SS (1981), he did not turn his mind to UHI, perhaps because it was a new phenomenon in the 1970s. When he conducted NIWA’s adoption of the 7SS in 1992, he again failed to take account of UHI. He was also a co-author of the NIWA report on climate station histories, Fuohy et al (1992), which extended over 250 pages but nowhere discussed the likelihood of UHI at any of the urban sites.

1910. Looking east to Albert Park 1902 from the city.

Hessell’s verdict was only partly accepted by the Review Report, in which NIWA classifies Auckland as “significantly influenced” by urban heating effects:

There is evidence that Albert Park warmed relative to other locations in the area between about 1928 and 1960 due to tree growth in the park and increased urbanisation around the park. The warming due to these effects over the three decades is estimated in the Auckland document at about 0.3°C. Such a warming would increase the apparent 1909–2009 trend at Auckland by 0.38°C.

In comparing the Albert Park record with that of Te Aroha, a hand-picked comparator, NIWA admits to finding evidence of a sheltering (not UHI) effect. There is no contrary evidence.

They obviously considered discarding Auckland, and explain that this would reduce the overall NZ Temperature Record to 0.81°C.

Rhoades & Salinger (1993) say:

Where long-term homogeneous series are required, for example, for studies of climate change, it is best to choose stations that are unlikely to have been affected by gradual changes in shading or urbanisation. This is no easy task. Karl et al (1988) have concluded that urban effects on temperature are detectable even for small towns with a population under 10,000.

Hessell points out that it is worse if both flaws appear together:

In the case of Auckland City the decrease in minimum temperatures due to sheltering (wind reduction) appears to have been masked by the urbanisation (building heat emittance) effect.

But there might be a remedy in some cases:

Climatic temperature trends can only be assessed from rural sites which have suffered no major transformation changes in shelter or urbanisation or from sites for which records have been made homogeneous.

NIWA’s scientists accept that Auckland’s eccentric warming trend alone raises UHI suspicions, but says (RR, p 35) “it is not easy to determine” just how much the urban growth affected the temperature series.

They toyed with the idea of making Albert Park’s records homogeneous by “successively reducing the annual temperatures by 0.01°C more each year than the previous year” (RR, p 6, footnote 1), but did not pursue the idea.

In the end, NIWA elected to take no action at all — and retained the Auckland record, warts and all, subject only to their own adjustments. They state lamely that (RR, p 37) “further research is required to provide more confident bounds on the correction of the early Auckland record for non-climatic warming.”

1910. Looking east to Albert Park 1902 from the city.

1928–60 only?

The sole reason NIWA offer for excluding the period before 1928 is that their chosen comparator station, Te Aroha, has unreliable records up to 1927. This leaves them with the choice of finding another comparator or making the blind assumption that sheltering didn’t begin until Te Aroha was reliable. They opted for the latter course.

In his thesis, Salinger states the view that the Albert Park trees “reached their maximum height in 1930 and it is not expected that they will further affect the exposure.” No evidence was offered and the statement appears to have been a guess — but it offers some evidence that shelter variations during the 1909-28 period were probably at their worst.

And the assumption that contamination ceased in 1960 is equally dubious. It is based on the fact that after 1960 there is no relative trend between Albert Park and two nearby comparators.

One chosen comparator is Riverhead Forest, itself affected by a “forest heat island” effect. NIWA comments (RR, footnote 29) that “forested sites in NZ are often noticeably warmer than non-forested ones.” For obvious reasons, Hessell excludes all “Forest Service stations” which were “planted adjacent to or amongst newly planted exotic forests.” If the trees at Riverhead were growing as fast as those at Albert Park, then the lack of relative trend would demonstrate that both sites were equally contaminated.

The other comparator is Mangere, which was built on the sewage treatment ponds in the 1950s. Apart from being in the midst of a seething stew of chemical reactions, the Mangere area must surely have experienced the highest urbanisation index in New Zealand during the relevant 1950-80 period. The population of Manukau City rocketed 1200% — from 15,700 in 1951 to 190,000 in 1981. If Mangere and Albert Park showed the same warming trend during 1960-76, then the latter was almost certainly affected by UHI.

2000s. Looking east showing mature trees.

So all the available indications are that Albert Park was affected by UHI/shelter throughout its 1909-76 life, rather than just the 1928-60 period admitted by NIWA. If shelter alone caused contamination of maximum temperatures of 0.18°C/decade as found by NIWA (RR, p 37), then maxima were 1.21°C higher than they ‘should’ have been over the life of the site. If Hessell is right, and minima are masked by UHI, we cannot know what they ‘should’ have been.

Even if minima were totally unaffected, Albert Park’s raw data needs to be reduced by a very substantial 0.7°C.

Mangere/Auckland Aero

The above discussion is confined to Albert Park and assumes its sole contamination problem was shelter, not UHI. No such assumption could be made about the two sites which were established in Manukau City during the period of its greatest expansion. This was also the period that Auckland International airport and the Mangere sewerage plant were established.

NIWA shows that Albert Park was 0.6°C warmer than Mangere at the changeover in 1976. That’s no doubt because Albert Park had accumulated non-climatic warming for 67 years, while it had been happening at Mangere for only 25 years. Significantly, their respective ongoing warming trends during the overlap period were identical.

2002. Most of the trees now are enormous.

NIWA did not check Mangere against Te Aroha or any other UHI-free station. If UHI in fact contributed non-climatic mean warming of 0.09°C/decade at Mangere/Auckland Aero, then another 0.3°C needs to be subtracted from the Auckland total.

Derivative Warming

What effect would an Albert Park correction have on the series? Quite a lot. NIWA says that omitting Auckland would reduce the series trend by more than 0.1°C. But it doesn’t stop there. The trend at Albert Park was used as a comparator to increase the warming trend at:

Masterton in 1942 (RR, p 50) and 1920 (p 52)
Wellington in 1928 (p 67) and 1912 (p 70)
Nelson in 1932 (p 90) and 1920 (p 92)
Hokitika in 1928 and 1912 (p 114)
Dunedin in 1912 (p 162)

So all of that ‘derivative’ warming also needs to be undone.

Perpetuated Warming

NIWA’s Schedule of Adjustments for the 7SS, tabled in Parliament on 19 February 2010, suggests that a key reason for moving the Auckland weather station from Albert Park to a less built-up site (Mangere) was because there were indications of urban warming.

So when it came to merging the records of the Albert Park and Mangere sites, NIWA knew that the late readings of the former were likely contaminated and unreliable. But they simply ignored this fact. In Figure 3 (RR, p 18), they compare the shelter-inflated readings from Albert Park (without adjustment) with the readings from Mangere. It’s no surprise that they find a base level difference of about 0.7°C — the prima facie UHI/shelter figure suggested above.

If proper allowance was made for UHI/sheltering, the base level temperatures of the two stations would be very similar. No significant adjustments would be necessitated by the site change.

Modern shot of the rotunda.

Ignoring UHI, NIWA subtracts 0.65°C from the Albert Park record from March 1976 all the way back to commencement of the series in September 1909. This one adjustment changes the raw data by a time-weighted aggregate of 41.67°C and accounts for nearly half the warming shown by all the adjustments in the NZT7 (see Schedule of Adjustments).

The Role of the BoM

The 2010 Review is the first time NIWA scientists have acknowledged any detectable non-climate influences in the temperature trend of any of the seven stations. It is also the first time their efforts have been open to influence by any outsider.

The Australian Bureau of Meteorology (BoM), which NIWA retained as a consultant for the Review, has long been conscious of the potential depredations of UHI on long temperature series. As NIWA’s trans-Tasman counterpart, it maintains the Australian Temperature Record, based on “high quality data sets (HQDS)” of about 100 stations — which exclude all data from the major cities.

During the consultancy, on 13 October 2010, the BoM issued a media release stating that they always knew city night-time temperatures (i.e., minima) were affected by UHI and added: “We can now confidently say that the reason our cities are warmer, and warming faster, than the surrounding countryside during the day is (also) urbanisation.”

The BoM research team analysed data from 70 sites from towns with populations of 500 to 100,000, as well as a handful from large cities.

The results were described at a meeting of the American Meteorological Society on 26 January 2011. It found that daytime (maximum) temperatures in Sydney and Melbourne were increasing at rates of 0.08°C and 0.07°C per decade faster than the average of the 73 sites.

BoM offers no solutions or corrections for UHI-affected sites. It just steers clear of them.

What should have been done?

As NIWA says above, it’s not easy to determine how much historical records were affected by UHI/shelter at any time. So it is not easy to effect a cure.

Hessell divided all stations with continuous records (and no major site changes) during 1930-79 into two categories. Those which seemed to have shelter/UHI problems were “A” stations, whilst the rest were “B”. He found that the average increase in mean temperatures at “A” stations was about five times that of the “B” category. The “B” stations showed no overall warming trend at all.

He paired nine urban stations with adjacent rural ones, and found all the former to be significantly warmer. After using further statistical measures, he concludes firmly:

It is thus considered that urbanisation is a significant factor in influencing the temperature regime of a district, and that this is an important contributor to temperature trends in growing built-up areas.

The usual response is to simply by-pass UHI-affected sites and focus on rural readings. But there were no rural stations in 1909. The 7SS include the four largest cities, while Masterton, Hokitika and Nelson are also substantial urban areas. All were growing vigorously during the early-mid twentieth century.

Perhaps Lincoln might qualify as rural. But, ironically, it was cursed by repetitive shelter belt problems during 1910-43.

Hessell was adamant that “the factors which have affected the reported temperatures at Auckland are common to many sites in New Zealand” and indicted Christchurch Gardens and Kelburn in particular. He regarded Dunedin as so unreliable that he did not even test it.

At the commencement of its Review, NIWA ought to have transparently tested all seven stations, at decadal intervals, for indications of gradual non-climatic temperature change. If NIWA or BoM had any disagreement with the tests or findings of the long-respected Hessell paper, they ought to have challenged them with a peer-reviewed journal paper of their own.

Where UHI/shelter problems were identified, NIWA should have made an earnest attempt to identify and correct for the impacts. Where this could not be done with 95% confidence, the defective site ought to have been dropped from the series.

13 Thoughts on “NZT7 uses defective raw data

  1. Mike Jowsey on April 19, 2011 at 12:04 am said:

    Excellent article Mr. Treadgold. One of your finest, imo. Thank you for the detailed research you have put into this. I predict NIWA will treat it the same way they treat UHI – if they don’t like the facts, ignore them.

  2. This article was a team effort, Mike, like many others. But they’re all written for the same purpose — to inform. Thanks for the kudos!

  3. Alexander K on April 19, 2011 at 8:47 am said:

    An excellent article, Richard and your team.
    When I was a teenager over a half-century ago, I was mad on flying and spent a lot of hours at aerodromes such as Milson watching and sometimes cadging a ride in light aircraft.
    I remember the Stephenson screen sited not far from the little wooden control tower and the fire pool. Milson has changed dramatically since then and I would be very interested to see where daily temp readings are taken today.
    The history of NIWA is also interesting and I am fascinated by the colleagial links with the UEA and the CRU over the years.

  4. Doug Proctor on April 19, 2011 at 5:35 pm said:

    Could we get a graph that shows what we think the temperature trend in NZ should look like? Even if it is a bit off, what is more reasonable that the NIWA 1 & 2?

    Regardless of the reasons, it comes down to the trend. The trend needs to be different from NIWA claims to have any reason for continued discussion. The difference from other parts of the world, other parts of the oceans, is significant. The number of stations is relatively small, much fewer than what many American students of statistics have reviewed.

    What is the NZScCoalition’s take on the NZ temp history in graphical form? It must be done already if a challenge was made to the courts.

    If it is out there already, I apologize: maybe it could be in the masthead, like NIWA had.

  5. Hemi Mck on April 19, 2011 at 6:47 pm said:

    I recently had a conversation with a scientist working then for the Ministry of Works involved in a detailed study on the before and after effects on climate of the Clyde Dam. It involved setting up several testing stations and a number of years of study. As part of this they decided they needed to test their thermometers, the same type used by Met Service. This was a standard test against the triple point of water. They rejected 10% of the new thermometers as outside acceptable bounds. This testing, I was told, had never been done by the Met Service prior to that time.

    Is there a record in NIWA of the actual thermometers used at each of the sites, when they were changed or moved? What is the life of a thermometer?


    Hemi, I managed to put this under the correct post for you. I regret I cannot guarantee similar service in the future! — Richard

  6. This is interesting information, Hemi. I’ll contact Willem de Lange, who takes some interest in weather stations and has contributed NZ data to the SurfaceStation project at WUWT. There are many points of error or simple doubt with the temperature record.

  7. No, you haven’t missed it, Doug — there is none. Nobody else can afford the time for it so far. The Coalition has a small group looking at NIWA’s work, which is where the court case originated, but we’re not doing a new, independent analysis. I mean, we’re not starting from scratch to produce a valid NZ temperature series. We’re simply examining NIWA’s work to see if it contains errors.

    To produce a whole new time series, one must first perform time-consuming studies that let you make decisions on which to base much time-consuming work, which needs to go through time-consuming checks, then pass through time-consuming peer review, and so it goes on…

    The court challenge is to show the official temperature record contains serious errors. Of course, since then NIWA has produced a new series, so who knows what will happen next?

    The Coalition wonders about using only seven stations, and those particular stations, and about other “metadata” matters affecting the quality of the records. It has questions about the methods used to adjust the raw readings. But none of this is settled and ready for public review. To help assess the new NZT7, I’ve asked NIWA for their correspondence with the BoM, who reviewed NIWA’s report. But they declined, so I immediately appealed to the Ombudsman, who informed me last week that they’ve only just started their inquiry.

    We can say that it’s odd the new NZT7, released last December, should reach the very same conclusion as the first one (0.91°C per 100 years). So there could well be errors and/or faulty data in it. Oh — read the above post!

    And all the while, the global warming science questions get all trampled on and covered over in a giant soup and it’s hard to know what’s true.

  8. Richard C (NZ) on April 19, 2011 at 9:00 pm said:

    Yes Doug, I agree. I’ve been advocating a 3rd order polynomial trend (a curve) and I think I’m getting traction with Barry B at least.

    A linear trend on this data is anathema to me but I concede it wont go away but why not present an alternative that better represents the data.

    If you’ve got a Google account, Here’s the NZT7 polynomial trend:-

    https://docs.google.com/leaf?id=0B4_i4MX8e3UaZDNlYzY2ZDUtYWVkZi00OGE2LTliZTUtZDVmZWUyNzFiZjVi&hl=en

    And the NZT7 location polynomials

    https://docs.google.com/leaf?id=0B4_i4MX8e3UaNGQ0NjZmYjAtMTc1NS00N2FjLWEzYzEtNWZiZTFiZjI3Mjdi&hl=en

    There’s a strong indication from the curve that there’s a cool phase on the way I think but you wouldn’t know that going by NIWA’s trend.

  9. Clarence Kay on April 21, 2011 at 3:14 am said:

    I though a “time series” was a comparison of the same thing at different points of time.

    The Albert Park weather station seems to have been a constantly changing thing. Its weather record compares the temperature of an exposed site at one time, with that of a partly wind-sheltered site at another time, and that of a fully-shaded site at a further time.

    How can a “trend” be found when there are so many variables?

  10. Doug Proctor on April 21, 2011 at 9:24 am said:

    Richard C & Richard T,

    Thanks for your responses! There are so many internal inconsistencies and contradictions in the IPCC/Hansen/Gore claims that I can only think that the health of the forest is considered somehow apart from the health of the trees. Like how polar bears are endangered as a species, but individual polar bears are not and so suitable as hunting trophies on a game-room wall.

    CO2 “warming” means that all heat in the oceans and non-oceanic surface comes from a downward heating of a warmed atmosphere. The speed with which heat penetrates 750 m into the oceans from a contact (and wind/wave turbulence) seems unlikely. After all, the air over the sea has warmed only 0.23C or so since 1979. If it were the sun’s rays, as they penetrate >60m and are powerful, seems more reasonable.

    A 50 ppmv increase in pCO2 at 3.75 W/m2 is 0.51 W/m2, meaning that at the end of the rise there is a 0.51 W/m2 increase in power, while an AVERAGE increase of 0.25 W/m2. This is on top of a current atmospheric absorption (clear skies) of 68 W/m2 and a land/sea absorption of 236 W/m2. Those of us who have swum in Northern lakes during 35*C summers know how thin the warm water is all through summer. Heat doesn’t want to go down. But apparently 0.25 W/m2 of warming by CO2 over the last 30 years flows through and is obvious beyond a 68 W/m2 clear air absorption and 236 W/m2 substrate absorption BACKGROUND.

    Pretty amazing how we can say that we know the energy in and out of 304 W/m2 with a confidence that during the year and between years there is no local or longterm change within 0.1 W/m2 (assuming that “real” has to be at least 2X SD). Yep, we are confident to 0.033% accuracy 95% of the time. Ignoring the albedo variation from a background 100 W/m2.

    340.5 W/m2 +/- 0.1 W/m2, day to day, year to year, place to place consistency. No long-term deviation at a planetary level from that, no sir. Or local, either. Frankly, this is the first part of the IPCC meme I can’t be comfortable with. And without strong feedback mechanisms to keep our planet the near-stable temperatures it experiences, not acceptable to the IPCC meme. And there is the second part I’m not comfortable with.

    And I haven’t even gotten to the temperature records in New Zealand or elsewhere.

  11. Richard C (NZ) on April 21, 2011 at 10:33 pm said:

    Doug, this comment is relevant to the post “Now Gluckman wants evidence too” so I’ve duplicated it as a reply to a comment of mine because it addresses exactly the same issues as I have touched on, It’s great to see your understanding of the core science of AGW, there’s not the same at our opposition blog Hot Topic and the more people that contribute here in this vein, the better. The duplicate is here:-

    https://www.climateconversation.org.nz/2011/04/now-gluckman-wants-evidence-too/#comment-49828

    I’ve replied to it there and you may wish to add more of your views on that, also the topic of that post and the other comments under it.

  12. LDLAS on April 22, 2011 at 3:47 am said:

    This is a no brainer.
    There hasn’t been significant warming since at least 1970 (40 years!) according to the NZT7.
    Just take into account the influence of the niño’s and nina’s and the volcanoes.

  13. Richard C (NZ) on April 23, 2011 at 10:56 pm said:

    Does anyone know what NZ regional temperature data is supplied to Hadley (or CRU or wherever) for the global record of this region?

    Is it raw CliFlo data? Adjusted (by whom)? What locations? Or is it composite?

    From what I understand, NZT7 is not included (why not?)

    Why is the same data not used for both regional record and global? Does not the NZ component of the global record bear the same scrutiny as the NZT7?

    So many questions.

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