"local and have a negligible influence on global warming trends" a new peer reviewed paper published in the Journal of Geophysical Research contradicts this. (Reported by CO2 Science)
Yang, X., Hou, Y. and Chen, B. 2011. Observed surface warming induced by urbanization in east China. Journal of Geophysical Research 116: 10.1029/2010JD015452.
What was learned
The three researchers say their findings indicate that "rapid urbanization has a significant influence on surface warming over east China," noting that "overall, UHI effects contribute 24.2% to regional average warming trends," and that "the strongest effect of urbanization on annual mean surface air temperature trends occurs over the metropolis and large city stations, with corresponding contributions of about 44% and 35% to total warming, respectively," with UHI trends of 0.398°C and 0.26°C per decade. And they say that due to other considerations, the UHI warming trends and their contributions to the overall warming over east China provided in their paper "can still be regarded as conservative."
What it means
The Chinese scientists conclude that if such UHI trends continue, "certain metropolitan areas may experience a rate of warming well beyond the range projected by the global climate change scenarios of the IPCC," referencing Stone (2007), while adding that "the increasing divergence between urban and rural surface temperature trends highlights the limitations of the response policy to climate change [that] focus only on greenhouse gas reduction," citing Stone (2009). And, of course, their findings call into serious question some of the basic conclusions of the IPPC, such as the organization's claim that UHI effects "have a negligible influence on global warming trends."