From CO2Science: Quereda et al. (2016) begin their work by stating that although “it may be accepted that urban heating is of local importance, there is no evidence that it alters the global temperature trend,” citing the IPCC (2001). However, they backtrack significantly in this regard throughout their analysis of the subject by stating that “on comparing the temperature of urban areas and rural areas, various researchers have concluded that the urban effect could account for between 40% and 80% of the observed thermal trend in the last few decades,” citing the studies of Ren et al. (2007), Yan et al. (2010), and McKitrick and Michaels (2007), who concluded that half of the warming trend observed between 1980 and 2002 could have arisen from changes in land use.
Paper Reviewed: Quereda, J., Monton, E., Quereda, V. and Molla, B. 2016. Significant Climate Warming (1950-2013) in the Spanish Mediterranean: Natural Trend or Urban Heat Island (UHI). Tethys 13: 11-20.
In studying the subject in even more detail over the 1950-2013 period, it was further found that this phenomenon could “account for between 70 and 80% of the recorded warming trend in Western Mediterranean cities.” And in light of this discovery, Quereda et al. pose the important question: “are urban areas contributing to the observed warming trend on which climate change is based?” to which they respond by stating that “the answer to be drawn from our analysis is fully affirmative.” And so they conclude by stating that “in these Western Mediterranean cities, the Urban Heat Island could account for up to 80% of the recorded warming.”
Mckitrick, R.R. and Michaels, P.J. 2007. Quantifying the influence of anthropogenic surface processes and inhomogeneities on gridded global climate data. Journal of Geophysical Research: Atmospheres 112. doi:10.1029/2007JD008465.
Ren, G.Y., Chu, Z.Y., Chen, Z.H. and Ren, Y.Y. 2007. Implications of temporal change in urban heat island intensity observed at Beijing and Wuhan stations. Geophysical Research Letters 34, L05711. http://dx.doi.org/10.1029/2006GL027927.
Yan, Z.W., Li, Z., Li, Q.X. and Jones, P. 2010. Effects of site change and urbanisation in the Beijing temperature series. 1977-2006. International Journal of Climatology 30: 1226-1234.