Comments
Pielke Sr on Jones et al 2008 Playing Down 1C Urban Warming per Century over China
A new paper has appeared which provides further discussion of an issue (urban effects), as well as the existing bais, with respect to the accurate calculation of multi-decadal global surface temperature trends (and thanks to ICECAP and Warwick Hughes for alerting us to the paper). The article is
Jones, P. D., D. H. Lister, and Q. Li (2008), Urbanization effects in large-scale temperature records, with an emphasis on China. J. Geophys. Res., 113, D16122, doi:10.1029/2008JD009916.
The abstract reads
“Global surface temperature trends, based on land and marine data, show warming of about 0.8°C over the last 100 years. This rate of warming is sometimes questioned because of the existence of well-known Urban Heat Islands (UHIs). We show examples of the UHIs at London and Vienna, where city center sites are warmer than surrounding rural locations. Both of these UHIs however do not contribute to warming trends over the 20th century because the influences of the cities on surface temperatures have not changed over this time. In the main part of the paper, for China, we compare a new homogenized station data set with gridded temperature products and attempt to assess possible urban influences using sea surface temperature (SST) data sets for the area east of the Chinese mainland. We show that all the land-based data sets for China agree exceptionally well and that their residual warming compared to the SST series since 1951 is relatively small compared to the large-scale warming. Urban-related warming over China is shown to be about 0.1°C decade-1 over the period 1951-2004, with true climatic warming accounting for 0.81°C over this period. ”
and the conclusion reads
“In this paper we have considered two different and clearly distinct issues: the size of possible UHIs in two European cities and the possible influence from urban-related factors in large-scale temperature trends. With the first issue, there is a clear UHI influence in temperature records from centrally-located sites in London and Vienna of 1.5° and 0.3°C, respectively. The effect of this excess warmth (due to the city being there) however is irrelevant to temperature trends, for the periods studied. With data expressed as anomalies from 1961 to 90, trends for the city center and rural locations are very similar, so in this form the anomalies can be used in gridded temperature products (such as CRUTEM3v). These results only apply to these two cities, and clearly any effect on other cities can only be judged through similar analyses comparing city center and rural temperature time series.
In the main part of the paper, we assessed the effect of the second of the two issues on temperature records from China. We first compared recently homogenized temperature series [from Li and Li, 2007] with earlier work undertaken by Jones et al. [1990] and showed that the homogeneity assessments have no impact on average ‘Eastern Chinese’ temperature series developed from the 42 sites used in 1990 (see Figure 6). We then compared two “China” averages [CHINA-LI from Li and Li, 2007, and from the gridded data, CRUTEM3v, Brohan et al., 2006]. All series essentially show the same trends and interannual variability. We conclude from this that when sufficient temperature series are averaged over a relatively large area, the effect of homogeneity adjustments is negligible (see Figure 7). We caution that such a conclusion is only relevant for this one application. In order to produce detailed spatial patterns of temperature change (and almost all other possible applications) it is essential to adjust, where necessary, station temperature series for homogeneity.
Finally, we assessed the Chinese data for the second issue (possible urban-related warming). This is difficult in China, as there are few specifically designated rural sites. Instead, we used SST data from the seas to the east of China, as we can guarantee that these data are unaffected by urban-related warming. We admit that SST is a poor surrogate for a “rural” network and, a priori, expect the land data sets to warm with respect to the SST series. We show trends of temperature by season for three different periods (1951-2004, 1954-1983 and 1981-2004). The two land series do warm relative to the SST over the periods from 1951 and 1954, but this mostly occurs during the mid-1970s. Over the most recent period (1981-2004), when economic development and growth have been most rapid, the SST series warms very slightly relative to the two “China” land series. Taking the annual data for the longest period (1951-2004) implies a relative warming of the land relative to the SST series of about 0.1°C decade-1 in agreement with the recent Ren et al. [2008] study. Allowing for this urban-related warming component (in CRUTEM3v) still leaves a warming over China of 0.81°C over the 1951-2004 period and 1.13°C between 1981 and 2004.
This paper bends over backwards to argue for the retention of general warming over China, despite finding evidence that landscape change (in this case, urbanization) alters long term trends. What is really surprising and disappointing, is that the authors chose to ignore the range of issues with the surface temperature data set that we have presented in several papers; for example
Pielke Sr., R.A., C. Davey, D. Niyogi, S. Fall, J. Steinweg-Woods, K. Hubbard, X. Lin, M. Cai, Y.-K. Lim, H. Li, J. Nielsen-Gammon, K. Gallo, R. Hale, R. Mahmood, S. Foster, R.T. McNider, and P. Blanken, 2007: Unresolved issues with the assessment of multi-decadal global land surface temperature trends. J. Geophys. Res., 112, D24S08, doi:10.1029/2006JD008229
Pielke Sr., R.A., C. Davey, D. Niyogi, S. Fall, J. Steinweg-Woods, K. Hubbard, X. Lin, M. Cai, Y.-K. Lim, H. Li, J. Nielsen-Gammon, K. Gallo, R. Hale, R. Mahmood, S. Foster, R.T. McNider, and P. Blanken, 2009: Reply to comment by David E. Parker, Phil Jones, Thomas C. Peterson, and John Kennedy on “Unresolved issues with the assessment of multi-decadal global land surface temperature trends. J. Geophys. Res., 114, D05105, doi:10.1029/2008JD010938
and
Lin, X., R.A. Pielke Sr., K.G. Hubbard, K.C. Crawford, M. A. Shafer, and T. Matsui, 2007: An examination of 1997-2007 surface layer temperature trends at two heights in Oklahoma.Geophys. Res. Letts., 34, L24705, doi:10.1029/2007GL031652.
Somehow, the authors must conclude that since they responded to two of the eight issues that we raised in our 2007 JGR paper in their Comment
Parker, D. E., P. Jones, T. C. Peterson, and J. Kennedy, 2009: Comment on Unresolved issues with the assessment of multidecadal global land surface temperature trends. by Roger A. Pielke Sr. et al.,J. Geophys. Res., 114, D05104, doi:10.1029/2008JD010450,
that they can just ignore the other issues that we documented, as well as not even comment on the two issues that they disputed in our 2007 JGR paper. The exchange of perspectives, as given in the Parker et al 2009 Comment, is admirable and is the proper scientific method. However, ignoring these issues in the new Jones et al 2009 paper clearly illustrates a remaining disappointing lack of scientific balance in their articles.
Roger Pielke Sr’s Climate Science weblog: A New Paper Has Appeared “Urbanization Effects In Large-Scale Temperature Records, With An Emphasis On China” By Jones et al. 2008