CRU 3b – Urban Warm Bias in GHCN
Posted by Jeff Id on January 5, 2010
So I’ve learned a great deal playing around with the GHCN data, I think this is a reasonably significant post. Ya know, it’s hard to know anything until you try it yourself and I hope more of the readers here will. Again, there was a problem in my last CRU post, however, the more I look for it, the more avenues there are to explore. The issues have been corrected by avoiding the remaining possibilities in this post.
Of all the details worked out over the last two days, one is a decent gridded average of temperature data. Unfortunately for us skeptics it looks like Figure 1 which is pretty similar to the CRU plot.
Yes, there is warming according to our temp stations, but I don’t think comrade Phil Climategate Jones would like this curve, because the warming in this curve happens entirely after 1975.
It’s nice to see a good quality CRU similar curve after the previous effort, but that’s how things happen when you do your work in public. The plot above uses all the data with each 5 digit temp station code averaged together individually, as my first post did. Anomaly is calculated over the entire series length.
The concern which was explored in some detail, regarded the hypothesis that the loss of stations in recent years created or biased the trend. It came about since so many stations are lost in recent years as Ken Fritsch pointed out in the recent CRU #3 thread.
I’ve run dozens of plots over the last several days, some of which contained an error in them created from data selection or a code problem in my previous post. Using the algorithm which averages together individual station ID numbers, I get very consistent CRUesque patterns. the warming is common to a variety of data sorting processes. This methods avoids the issues of data selection or code problems in the other methods and I’m confident in the accuracy of these results, but you should check them.
Several methods were employed to test the consistencey of result, including sorting for Rural and Urban, and sorting for several different time lengths of station data. All varieties so far produced very similar same results. There are, however, interesting revelations from examination of the slight differences.
Figure 3 is a plot is the urban data only. Of note is that the warming starts at 1978 with only slight warming beforehand and launches up about 1.2 C with no end in sight. Also, 1982 isn’t much reduced from around 1940 which is different from the global average in Figure 1. So the next thing I did was to plot the rural data.
That looks a great deal more like the satellite data. The temp rose and fell again prior to 1978 and rose again since 1978 is maybe 0.5C total. I tend to ignore data prior to 1900 due to the very small number of stations. I don’t think the drop in temps to 1900 levels in the early 70’s is the kind of curve that supports the high CO2 sensitivity claimed by climate science. Does anyone remember the snow storms of the early 70’s? Yeah, yeah just weather, I know.
One of the other avenues explored at great length , yet still isn’t finished, was how station starts and stops affect the trend in recent years. To explore that, one of the several methods I used was to sort data according to number of available data points. Below, I presented the gridded global average for all stations with at least 100 years (1200 points) of available data, since many of the stations in Figure 2 were started in 1950.
The urban data only in Figure 5 has an even steeper curve, you would expect this from longer series in this type of analyis. The temp rise since 1978 is about 1.2C. The rural 100 year curve is below.
So the Rural stations show about 0.7C of warming since 1978. Visibly less warming than the urban stations by themselves. Also note the slight downtrend in recent years. Since the industrial revolution occurred a hundred years ago, it’s hard to imagine this curve is created by CO2. Still I’m not denying the heat capturing ability of CO2, just that the curves here don’t show a continuous warming but rather a short term recent spike.
So of course we should look at the difference between urban and rural stations.
Look at that curve! Despite the crudeness of the categorization of thermometers, there is a clear warming bias for big city data. The curve in Figure 8 ends at 0.6C difference. What’s more, the trend between the two looks statistically significant. If Phil Climategate Jones and Michael Marx Mann can choose which data they want to show and hide the rest, I think it’s only fair to choose to look at trends only from Figure 8 since 1978 (even though it won’t make much difference). After all, one hundred percent of global warming has apparently occurred since that time. Let’s do a simple significance test.
Woah, it’s not even close, a trend of 0.12 and a no trend null hypothesis limit of +0.04. The difference between urban and rural warming is as great as the entire trend in UAH data over the same timeperiod.
Just how much trend do the ground stations show.
Even Figure 11 is still greater than UAH and RSS satellite data but it’s one heck of a lot less than the urban stations. Of course we would be remiss to not mention that WUWT has taught us what rural stations often look like.
What could go wrong with sophisticated technology like that?