A couple of years ago, before I got involved in proxy studies, I was interested in the UHI question and wrote to Phil Jones to request the data used in Jones et al 1990, his study purporting to show the unimportance of urban warming. Jones said that it was on a diskette somewhere and too hard to find, Jones observing that the study had been superceded by other studies. (“Moved on” ?) Anyway, that was before I was wise to the ways of the Team and I didn’t pursue the matter.
However, Jones et al 1990 continues to be relied upon; it’s cited in recent literature and in AR4. So I thought that it would be interesting to re-visit the matter. I still don’t know what sites were used, but something turned up anyway.
Peterson 2003 reviewed literature on UHI and reported that, even in 2003, Jones et al 1990 was one of only two studies that used”homogeneous” data:
Only two large-scale studies were found that used homogeneous data. These are the time series analyses of Peterson et al. (1999) and the Russian and Chinese regions of the analyses presented in Jones et al. (1990). These analyses found no indication of significant urban influence on the temperature signal.
Elsewhere in the article, Peterson 2003 stated:
Jones et al. (1990) determined that the impact of urbanization on hemispheric temperature time series was, at most, 0.058 deg C century-1. This result was based on the work of Karl et al. (1988) for the United States and further analysis of three other regions: European parts of the Soviet Union, eastern Australia, and eastern China. In none of these three regions was there any indication of significant urban influence in either of the two gridded time series relative to the rural series’ (Jones et al. 1990). The homogeneity assessments varied with regions. The data for one region were assessed for artifacts due to factors such as site moves or changing methods used to calculate monthly mean temperatures.’ Another region used data from stations with few, if any, changes in instrumentation, location or observation times.’ The homogeneity of data used in the third region was not discussed. Their results showed that the urbanization influence is, at most, an order of magnitude less than the warming seen on a century scale.’
IPCC 4AR cited Jones et al 1990 twice as follows:
Urbanization impacts on global and hemispheric temperature trends (Karl et al., 1988; Jones et al., 1990; Easterling et al., 1997; Peterson, 2003; Parker, 2004, 2006) have been found to be small.
Many local studies have demonstrated that the microclimate within cities is on average warmer, with smaller DTR than if the city were not there. However, the key issue from a climate change standpoint is whether urban-affected temperature records have significantly biased large-scale temporal trends. Studies that have looked at hemispheric and global scales conclude that any urban-related trend is an order of magnitude smaller than decadal and longer timescale trends evident in the series (e.g., Jones et al., 1990), a result that could partly be attributed to the omission from the gridded dataset of a small number of sites (<1%) with clear urban-related warming trends.
So Jones et al 1990 is still relied on in the literature. Jones said that they selected 38 non-urban sites in western Russia (the sites are not identified) and that in the 1930-1987 period, there was a cooling of about 0.2 deg C in the rural stations (RUSSR), as compared with a lesser cooling of ~0.1 deg C in the Jones network (JUSSR):
For the western part of the Soviet Union we selected a network of 38 stations from sites in non-urbanized areas with long records (Figure 1a). The sites include isolated meteorological stations, lighthouses, villages and other small settlements. The largest populated sites are nine towns with populations of the order of 10,000 people. All nine towns are located at least 80 km away from major cities. All the site records were assessed for artifacts due to factors such as site moves or changing methods used to calculate monthly mean temperatures. At 12 sites the observing station was moved slightly. Comparisons with neighboring sites were made before and after each change and ,w here necessary, corrections were made to ensure homogeneity of the rural station record, No corrections were deemed necessary for the remaining 26 stations where no station moves were reported.Over the 1930-87 period, a cooling of about ~0.2 deg C is observed in RUSSR. This cooling is about 0.1 deg C smaller in JUSSR but there are no statistically significant differences between the two series.
Jones also says that 60 station records were used to construct the gridpoint series, of which 25 stations in operation by 1901 and 32 were operating in 1987 and that there were 4 stations common to the gridpoint and rural time series. In the caption to Figure 2, he also says of the 38-site rural network that 20 were contributing in 1901; that 7 began recording after 1930 and that the number of missing values from 1930-1987 was 8% of the total. In addition to ~0.09 cooling trend in the Jones network from 1930 to 1987, he also reported (Table 1) that there was a 0.31 deg C upward trend from 1901-1987.
Their Figure 2a shows a plot of the temperature anomaly from their rural network (the comparandum Jones network plot is not shown). For comparison to their Figure 2a (shown a bit lower down), I made up a network of 41 HadCRUT3 gridpoints (this is a 5×5 network, while Jones used a 5×10 network). The network is shown here and can be compared to Jones et al 1990 Figure 1a.
Next here are plots showing first the rural network from Jones et al 1990 and then the annual average of the 41 gridpoints identified above for 1901-1988, showing the 1930-1987 trendline. The appearance of the two plots is similar. Jones et al say that their figure is for 1901-1987, but the closing uptick occurs in 1988 in HadCRUT3 rather than 1987. Maybe Jones actually plotted to 1988 – who knows?
The HadCRUT3 linear trend is 0.24 deg C over the period 1930-1987, as compared to a reported -0.09 deg C cooling in the Jones et al 1990 gridded series (and -0.21 deg C in the rural series). So there is 0.45 deg C difference in the 1930-1987 period between HadCRUT3 and the rural network used to show that the difference is less than 0.05 deg C per century. Since the Team is involved, one also has to pay attention to little discrepancies like 1987 versus 1988 endpoints – why would they calculate the trend on 1987 rather than 1988 if 1988 is illustrated in the plot? With the addition of 1988, the linear trend increases to 0.30 deg C over the period, increasing the discrepancy to 0.51 deg C over 1931-1987 between the rural network and HadCRUT3 – as compared to the reported 0.09 deg C in Jones et al 1990.
Over the 1901-1987 period, the estimated linear trend in the HAdCRUT3 network is 0.44 deg C (1901-1988: 0.49 deg C), as compared with a reported linear trend of 0.38. This difference between versions is much less than the 1930-1987 difference. It’s hard to figure out exactly what’s going on here, as long as Jones refuses to identify the stations or release the data. Despite the many citations, it doesn’t appear that anyone, including the IPCC, has ever tried to directly verify these results. Does this study still stand for the proposition that UHI effects have been shown to be inconsequential? Well, the Coordinating Lead Author of this AR4 chapter was, um, Phil Jones. No one ever said that the Team needed a big locker room.
Thomas C. Peterson, 2003. Assessment of Urban Versus Rural In Situ Surface Temperatures in the Contiguous United States: No Difference Found. Journal of Climate Volume 16, Issue 18 (September 2003) pp. 2941—2959 http://www.ncdc.noaa.gov/oa/wmo/ccl/rural-urban.pdf
Jones, P.D., et al., 1990: Assessment of urbanization effects in time series of surface air temperature over land. Nature, 347, 169—172.
Warwick Hughes, http://www.warwickhughes.com/papers/90lettnat.htm