Comparison of the NIWA 7 Station data to GHCN and GISS
February 6, 2010Posted by on
In my post about how to prove your adjustments to a temperature record I mentioned a few things about the data New Zealands version of the US NOAA, NIWA, used in a 7 station dataset to show their adjustments are correct. I pointed out that there is no set standard in making adjustments and that those differences can get you different results, such as NASA GISS discards the Auckland temperature record where NIWA includes it. So I decided to gather records from the NCDC GHCN Adjusted Dataset, NASA GISS and compare them to the NIWA 7 station dataset. First thing was I had to set a baseline. NIWA uses the 1971-2000 Baseline, GISS uses the 1951-80 Baseline and for most graphs and maps I had seen from NOAA they use the 1961-90 Baseline.
After looking at the datasets I went with the 1961-90 Baseline since that way I could get the most records into the base period for NZ. So since I already had a copy of GHCN mean_adj on my computer (Dec 09 Ver) that set the upper limit for the timescale and since GISS goes back no further then 1880 and the first year GISS has Data for NZ is the year 1881. So all graphs will be between the years 1881 and 2007 for the Baseline 1961-90. I then selected the stations from the GISS and GHCN station lists based on the simple criterion they had to meet a requirement of 25 years minimum in the baseline period. That made it 12 stations in the GHCN dataset and 10 from GISS.
So first I copied the GHCN data into my spreadsheet program (I use OpenOffice 3.1) and calculate the average mean temperature for each year at each station. From this I then calculated anomaly’s based on themselves for the selected baseline. From that I averaged the Anomaly’s the same way that NIWA averaged theirs in the 7 station series.
Next I copied in the data from GISS for each station ( http://data.giss.nasa.gov/gistemp/station_data/ ). GISS already calculated the average mean temperature so I just had to make anomaly’s for each station.
Then I copied in the NIWA 7 station dataset and made anomaly’s from the average temperature NIWA calculated.
When it was all said and done this is the graph I got:
So what does this tell us?
Well as you can see NCDC says that New Zealand is warming faster and its hotter then NIWA says by a good bit. On the other hand GISS says NZ has warmed less then .5 C over a century.
So what makes them all so different? The way they were adjusted.
A lot of the time you have more then one station at a location and they get combined. NCDC uses a method called the “First Difference Method” to combine records. GISS and according to what I seen from NIWA they both use the “Reference Station Method”. Now I don’t know if the way NIWA uses that method is the same as outlined by Dr. Hansen in his 1987 and 1999 papers. Also GISS checks “Urban” Stations against near by “Rural” Stations to try to remove UHI effects. The GISS method reguires 3 nearby rural stations that over lap the record of the urban staion by 20 years. This requirement is the reason GISS dropped Auckland from being in their final adjusted output, they couldn’t get 3 stations over the 20 year period, there was only 19 years (I know this because that is what Dr. Reudy of NASA GISS told me over a month ago when I discovered Auckland was in the GISS station list but had no output data and emailed them. I like to thank Dr. Reudy for his prompt reply and explaination).
Now the million dollar question: Who is right?
Now they all can’t be right, but they were all supposedly adjusted by methods in the peer reviewed literature. However as I put in my last post we do know that GISS released their computer codes on how they make their global product and it has been verfied to conform to the papers it is based on. So we can have greater confidence in the GISS numbers because of that. The NCDC numbers and the NIWA numbers all we got is outputs and papers but no code. So that give less credence to those numbers until such time as their computer codes are released and used independently by someone else and get the same results and match the steps to the papers they are based on.