Chinese climate scientists tactfully tell the IPCC that surface air temperature (SAT) trends over north China include a large component of urban warmingMarch 10th, 2009 by Warwick Hughes
Ren et al 2008 measure urban warming in a north China grid box 33 to 43 degrees North and 108 to 120 degrees East by comparing temperature trends in groups of stations of different population size for the period 1961-2000. For a concise summary of the Ren et al 2008 paper, Urbanization Effects on Observed Surface Air Temperature Trends in North China
Their results are summarised in their Table 3 copied here and they conclude from this, assuming no urban warming in their Rural series which warms at 0.18 degrees per decade that urban warming in their various station groups is as shown in their Table 4 below.
In view of the importance of IPCC global warming underpinning carbon reduction policies being considered by many nations, it seemed vital to compare the Ren et al trends against those for the Hadley Centre CRUT3 land only data which has provided the mainstay for IPCC warming claims over nearly 20 years. Ren et al did not compare their trends with any global gridded datsets.
Taking the Hadley Centre CRUT3 data for Ren et al’s north China grid box from the KNMI Climate Explorer website we find a warming trend of 0.31 degrees per decade over the 40 years 1961 to 2000. When compared to the Ren et al numbers in Table 3 we can see this warming trend is near the top of the range and indeed indicates urban warming of 0.13 per decade or equivalent to a rate of 1.3 degrees per century.
So, more evidence that IPCC data contains serious UHI contamination.
Quickly comparing the Hadley Centre CRUT3 land only data 1979-2008 for the north China grid box with the NASA MSU LT data from University of Alabama at Huntsville, all data downloaded from the KNMI Climate Explorer.
We find that CRUT3 warms at 0.57 degrees per decade, while the lower troposphere warms at 0.27, suggesting urban warming of 0.3 per decade. This comparison indicates that urban warming in north China has increased after 2000.
Ren, G., Zhou, Y., Chu, Z., Zhou, J., Zhang, A., Guo, J. and Liu, X. 2008. Urbanization effects on observed surface air temperature trends in north China. Journal of Climate 21: 1333-1348.