claim: Numerous studies into the effect of urban heat island effect and microsite influences find they have negligible effect on long-term trends, particularly when averaged over large regions.
evidence: Studies that have looked at hemispheric and global scales conclude that any urban-related trend is an order of magnitude smaller than decadal and longer time-scale trends evident in the series ( e.g., Jones et al., 1990; Peterson et al., 1999 ).