There is an important, well written new paper that provides further evidence that land use change significantly influences the use of surface air temperatures in these areas as part of the construction of a global average surface temperature anomaly.
The paper is
Rosenzweig Cynthia, William D. Solecki, Lily Parshall, Barry Lynn, Jennifer Cox, Richard Goldberg, Sara Hodges, Stuart Gaffin, Ronald B. Slosberg, Peter Savio, Frank Dunstan, and Mark Watson: 2009, Mitigating New York City’s Heat Island: Integrating Stakeholder Perspectives and Scientific Evaluation. Bulletin of the American Meteorological Society. Volume 90, Issue 9 (September 2009) pp. 1297–1312.
The abstract reads
“This study of New York City, New York’s, heat island and its potential mitigation was structured around research questions developed by project stakeholders working with a multidisciplinary team of researchers. Meteorological, remotely-sensed, and spatial data on the urban environment were brought together to understand multiple dimensions of New York City’s heat island and the feasibility of mitigation strategies, including urban forestry, green roofs, and high-albedo surfaces. Heat island mitigation was simulated with the fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5). Results compare the possible effectiveness of mitigation strategies at reducing urban air temperature in six New York City neighborhoods and for New York City as a whole. Throughout the city, the most effective temperature-reduction strategy is to maximize the amount of vegetation, with a combination of tree planting and green roofs. This lowered simulated citywide surface urban air temperature by 0.4°C on average, and 0.7°C at 1500 Eastern Standard Time (EST), when the greatest temperature reductions tend to occur. Decreases of up to 1.1°C at 1500 EST occurred in some neighborhoods in Manhattan and Brooklyn, where there is more available area for implementing vegetation planting. New York City agencies are using project results to guide ongoing urban greening initiatives, particularly tree-planting programs.”
The paper is not written specifically with respect to the issue of diagnosing regional representative multi-decadal surface air temperature trends. However, it clearly shows the magnitude of the effect of land use change on surface air temperatures. For example, Table 3 presents a summary of the effect of increased vegetation and higher surface albedo on urban air temperatures during heat waves for different areas of New York City. The average differences for different parts of New York range up to over 1 degree Celsius at 1500 EST and are even larger at individual locations for the maximum effect as shown in Table 4.
This paper effectively shows how deliberate land management can alter the urban temperature environment. It also shows that as the region became urban, temperature trends of these magnitudes occurred due to these landscape changes.
The new Rosenzweig et al 2009 paper, while silent on the issue in its text, is an effective rebuttal of the papers
Parker, D.E., 2004: Large-scale warming is not urban. Nature, 432, 290, doi:10.1038/432290a
Peterson, T.C., 2003: Assessment of urban versus rural in situ surface temperatures in the contiguous United States: No difference found. J. Climate, 16, 2941-2959.
As we have shown in
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
there remain significant issues with the use of surface air temperatures from land based observations, as a diagnostic of global warming and cooling.