The “inquiries” into CRU, as is well known, did not examine CRU’s “science”. One of CRU’s main “contributions” is the “proof” by Jones et al 1990 that the development of urban heat islands contributed no more than ~0.05 deg C to measured 20th century land temperatures. This proof is an integral component in justifying CRUTEM – which makes no allowance or adjustment for increasing UHI. Jones et al 2008 revisited this theme, estimating the UHI for London at 1 deg and New Yok City at 1.5 deg C, editorializing that much of this would have developed prior to the 20th century.
Jones’ failure to allow for developing UHI has occasioned much skeptical criticism over the years. Jones and the Team have used their offices as reviewers to quash criticism from appearing in print e.g. “going to town” as a reviewer on papers that had the temerity to criticize and, as IPCC review authors, to initial suppress and then include only with adverse editorial comment criticisms like McKitrick and Michaels 2004. The recent McKitrick and Nierenberg 2010 is the most recent entry in this longstanding debate, replying to and rebutting Gavin Schmidt’s comment on McKitrick and Michaels 2007 – all of which direct UHI indirectly.
NASA’s quantitative estimates of UHI are astounding:
The compact city of Providence, R.I., for example, has surface temperatures that are about 12.2 °C (21.9 °F) warmer than the surrounding countryside, while similarly-sized but spread-out Buffalo, N.Y., produces a heat island of only about 7.2 °C (12.9 °F), according to satellite data.
Zhang has an interesting graphic showing the dependence of UHI on ecology – comparing Baltimore, Dallas and Las Vegas. She observes that UHI has a particularly large impact in forested areas, while the impact in desert areas is relatively negligible.
Forest, around 10C, grass 5-6C, desert weak and sometime heat sink.
In Zhang’s presentation, she shows UHI for Lynchburg and Philadelphia with UHI of 5.5 deg C and 11.7 deg C respectively – postulating a log relationship to population (originally proposed by Oke in the 1970s.)
In an accompanying presentation here, UHI in Paris is estimated at 8 deg C at night and up to 10 deg C in some suburbs in the afternoon.
Also see presentation here.
The association of particularly large UHI with urbanization in forested areas seems especially relevant in assessing the Russian land temperature increases, long a sore point with skeptics. (And, needless to say, it was criticism of CRU’s handling of Russian data that Jones took particular umbrage against.)