New Paper “Decadal Variations In The Nocturnal Heat Island Of London” By Wilby Et Al 2011

There is a new paper that adds significantly to our understanding of the urban heat island, and thus its role on long-term surface temperature records. The new paper is

Robert L. Wilby,Philip D. Jones  and David H. Lister: Decadal Variations In The Nocturnal Heat Island Of London. Weather March 2011. DOI: 10.1002/wea.679

The abstract reads

“Our review of the long-term behaviour of London’s UHI provides a salutary reminder that the appearance and disappearance of trends in environmental data can depend very much on the segment of data analysed. Nonetheless, we can confirm – using both daily and monthly temperature records – that the summer nUHI did intensify between the late 1950s/early 1960s and the 1980s. This period coincided with an abrupt increase in the frequency of summer anticyclonic weather. There is also evidence of a slight rise in the annual number of intense heat-island events that can be linked to more persistent anticylonic weather systems at that time. A weak decline in summer nUHI since the 1980s coincides with a rise in the frequency of cyclonic weather. Since 1931, the summer nUHI has risen slightly, but not significantly. The overall annual mean nUHI does, however, show a weak but significant (p<0.05) rise when the monthly SJP record is compared to that of WIS.”

Their concluding remarks read

Our review of the long-term behaviour of London’s UHI provides a salutary reminder that the appearance and disappearance of trends in environmental data can depend very much on the segment of data analysed.
Nonetheless, we can confirm – using both daily and monthly temperature records – that the summer nUHI did intensify between the late 1950s/early 1960s and the 1980s. This period coincided with an abrupt increase in the frequency of summer anticyclonic weather. There is also evidence of a slight rise in the annual number of intense heat-island events that can be linked to more persistent anticylonic weather systems at that time. A weak decline in summer
nUHI since the 1980s coincides with a rise in the frequency of cyclonic weather. Since 1931, the summer nUHI has risen slightly, but not significantly. The overall annual mean nUHI does, however, show a weak but significant (p<0.05) rise when the monthly SJP record is compared to that of WIS.

 Over the 50-year daily record, less than half of the variance in the summer-mean nUHI signal is explained by synoptic weather patterns. This could be due to a number of factors. The weather types describe conditions across the British Isles generally, rather than for southeast England specifically. The conditions experienced within a given weather class are known to vary from day to day. There have also been marked changes in regional air quality in the wake of the notorious winter ‘smogs’ of the 1950s and the summer stubble burning
of the 1970s and 1980s. Other time-dependent factors (such as artificial heat sources, building albedo, thermal mass, sky-view factors, surface roughness, and vegetated area) may be locally important (McGregor et al., 2006). Furthermore, censuses show that the population of Greater London peaked in 1939 then fell until 1991 and has since risen again.”

This paper is an important new addition to the literature on multi-decadal surface temperature trends.

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