More on the NIWA New Zealand data adjustment story

Watts Up With That?
Saturday, Nov 28th, 2009

NIWA issued a response statement regarding the charges leveled by The NZ Climate Science Coalition here:

http://www.niwa.co.nz/our-science/climate/news/all/niwa-confirms-temperature-rise

They say:

Warming over New Zealand through the past century is unequivocal.

NIWA’s analysis of measured temperatures uses internationally accepted techniques, including making adjustments for changes such as movement of measurement sites. For example, in Wellington, early temperature measurements were made near sea level, but in 1928 the measurement site was moved from Thorndon (3 metres above sea level) to Kelburn (125 m above sea level). The Kelburn site is on average 0.8°C cooler than Thorndon, because of the extra height above sea level.

I’m not too impressed, especially when you see where the weather station for National Institute of Water and Atmosphere (NIWA) is, right on the rooftop next to the air conditioners:

Here is the station survey: NIWA_station_survey (PDF) and the Google Earth KML file

Thanks to: Dieuwe de Boer who did a good portion of station surveys in New Zealand last year.

The NZ Climate Science Coalition responds:

NIWA’s explanation raises major new questions

The NIWA climate controversy took a new twist tonight with the release of new data from the government run climate agency.

Reeling from claims that it has massaged data to show a 150 year warming trend where there isn’t one, NIWA’s chief climate scientist David Wratt, an IPCC vice-chair on the 2007 AR4 report, issued a news release stating adjustments had been made to compensate for changes in sensor locations over the years.

While such an adjustment is valid, it needs to be fully explained so other scientists can test the reasonableness of the adjustment. 

Wratt is refusing to release data his organisation claims to have justifying adjustments on other weather stations, meaning the science cannot be reviewed. However, he has released information relating to Wellington temperature readings, and they make for interesting reading.

Here’s the rub. Up until 1927, temperatures for Wellington had been taken at Thorndon, only 3 m above sea level and an inner-city suburb. That station closed and, as I suspected in my earlier post, there is no overlap data allowing a comparison between Thorndon and Kelburn, where the gauge moved, at an altitude of 135 metres.

With no overlap of continuous temperature readings from both sites, there is no way to truly know how temperatures should be properly adjusted to compensate for the location shift.

Wratt told Investigate earlier there was international agreement on how to make temperature adjustments, and in the news release tonight he elaborates on that:

“Thus, if one measurement station is closed (or data missing for a period), it is acceptable to replace it with another nearby site provided an adjustment is made to the average temperature difference between the sites.”

Except, except, it all hinges on the quality of the reasoning that goes into making that adjustment. If it were me, I would have slung up a temperature station in the disused location again and worked out over a year the average offset between Thorndon and Kelburn. It’s not perfect, after all we are talking about a switch in 1928, but it would be something. But NIWA didn’t do that.

Instead, as their news release records, they simply guessed that the readings taken at Wellington Airport would be similar to Thorndon, simply because both sites are only a few metres above sea level.

• A d v e r t i s e m e n t

Airport records temps about 0.79C above Kelburn on average, so NIWA simply said to themselves, “that’ll do” and made the Airport/Kelburn offset the official offset for Thorndon/Kelburn as well, even though no comparison study of the latter scenario has ever been done.

Here’s the raw data, from NIWA tonight, illustrating temp readings at their three Wellington locations since 1900:

What’s interesting is that if you leave Kelburn out of the equation, Thorndon in 1910 is not far below Airport 2010. Perhaps that gave NIWA some confidence that the two locations were equivalent, but I’m betting Thorndon a hundred years ago was very different from an international airport now.

Nonetheless, NIWA took its one-size-fits all “adjustment and altered Thordon and the Airport to match Kelburn for the sake of the data on their website and for official climate purposes.

In their own words, NIWA describe their logic thus.

• Where there is an overlap in time between two records (such as Wellington Airport and Kelburn), it is a simple matter to calculate the average offset and adjust one site relative to the other.
• Wellington Airport is +0.79°C warmer than Kelburn, which matches well with measurements in many parts of the world for how rapidly temperature decreases with altitude.
• Thorndon (closed 31 Dec 1927) has no overlap with Kelburn (opened 1 Jan 1928). For the purpose of illustration, we have applied the same offset to Thorndon as was calculated for the Airport.
• The final “adjusted” temperature curve is used to draw inferences about Wellington temperature change over the 20^th century. The records must be adjusted for the change to a different Wellington location

Now, it may be that there was a good and obvious reason to adjust Wellington temps. My question remains, however: is applying a temperature example from 15km away in a different climate zone a valid way of rearranging historical data?

And my other question to David Wratt also remains: we’d all like to see the metholdology and reasoning behind adjustments on all the other sites as well.

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