Whilst the possible warming from AGW in the last 100 years can be measured in tenths of a degree, a new study suggests that warming from urbanisation may be even more significant:
In the first study to attempt to quantify the impact of rapidly expanding megapolitan areas on regional climate, a team of researchers from Arizona State University (ASU) and the National Center for Atmospheric Research has established that local maximum summertime warming resulting from projected expansion of the urban Sun Corridor [the four metropolitan areas of Phoenix, Tucson, Prescott and Nogales] could approach 4 degrees Celsius. This finding establishes that this factor can be as important as warming due to increased levels of greenhouse gases. Their results are reported in the early online edition (Aug. 12) of the journal Nature Climate Change.
“The actual contribution of urban warming relative to summertime climate change warming depends critically on the path of urbanization, the conversion of natural to urban landscapes, and the degree to which we continue to emit greenhouse gases,” said Alex Mahalov, a co-author and principal investigator of the National Science Foundation grant, “Multiscale Modeling of Urban Atmospheres in a Changing Climate,” which supported the research.
“As well as providing insights for sustainable growth of the Sun Corridor and other rapidly expanding megapolitan areas, this research offers one way to quantify and understand the relative impacts of urbanization and global warming,”said Mahalov, the Wilhoit Foundation Dean’s Distinguished Professor in ASU’s School of Mathematical and Statistical Sciences. (source)
The abstract is here.