The Global Historical Climatological Network (GHCN) is a global climate data set maintained by the National Climatic Data Center. The GHCN is often used to monitor and detect climate change. The GHCN includes more than 6,000 individual climate stations that observe temperature although the number of stations in any given year may be significantly less. A global data set of monthly satellite-derived vegetation indices has been used, with ancillary information, to assess the urban heat-island effect on monthly average temperatures observed during the summer and autumn months. Stations were compared to their surrounding environment and identified as urban or rural. Generally urban stations exhibited estimated average monthly temperature differences of 1 degree (C) higher than their surrounding environment. Temperature differences between urban stations and their surrounding environment of as great as 2 or more degrees (C) were estimated based on the vegetation indices.