Nova and her friend Ken Stewart claim Australia’s homogenised data is adjusted to increase the warming by 70%!!! Ken’s major mistake is to ignore the difference in temperature when a site is relocated, or when multiple sites are combined into longer record.
Ken Stewart says… “Worst of all is Wangaratta”, let’s look.
Over time some sites are relocated and this happened in Wangaratta when the site was moved from the town, six kilometres to the south to the local airport. Ken’s naive mistake is to simply stitch together the data from both of these sites without regard for the difference in temperature between the two sites.
To understand why this is wrong, exaggerate the concept and think of what would happen if a site moved from Queensland to Hobart. Suddenly the temperature would have dropped many degrees from one set of data to the next. Unless this is corrected (adjusted, homogenised) you would wrongly assume the data shows dramatic cooling.
In the case of Wangaratta, looking at the raw data for the individual sites, Wangaratta City looks like this with almost no change …
The individual sites show no warming in the City up to 1985, then about 1.4°C of warming from 1988 onwards at the Aero site. But the important question to ask is how do these two sites relate? Is one site naturally warmer than the other on any given day? Ken’s amateur effort makes no effort to evaluate the difference, instead just gluing them together into one continuous record – a mistake that could make a dramatic difference to the long term trend as demonstrated in the following image.
As described in this document, substantial efforts are undertaken to ensure homogenisation is performed as well as possible. When the BOM recently created ACORN and declared that Australia had warmed by about 1°C in the last century, Wangaratta’s data wasn’t even included.
So Ken Stewart moved his attention to Alice Springs and repeated the same mistake …
In the case of Alice Springs the data is coming from two sites, Alice Springs Post Office (till 1953) and ten kilometres away, the Alice Springs Airport (from 1942). The more than a decade of overlap allows a comparison between the two sites; this shows the Post Office is a hotter location than the Airport. Simply combining the records, as Ken does, without accounting for the difference would erroneously lead to less warming. A simple adjustment to correct for the difference is shown in the following graph…
Ken’s failure to perform even this simple adjustment leads him to believe the records are unfairly adjusted.
And how does the warming look if you simplify things? Taking a look at just the Alice Springs Airport record gives a very clear insight into how little change there really is between the raw data and the ACORN data. In the following graph the ACORN record is slightly colder than the raw data. And climate denialists are always telling us the adjustments are always up!
Ken’s amateur effort is yet another reminder of why experts in their field are generally far better and more experienced than the casual web-blogger.