It is a common claim of climate change deniers that the earth isn't warming. They make spurious claims that the measurement is subject to large errors. With most of the long-term data coming from surface weather stations. Many of these are located in urban areas which have been expanding amd as a result all they are measuring is what is known as the "urban heat island effect".This occurs where urban areas are naturally warmer because they are constructed of different materials.
The facts show that there is no doubt that warming is taking place. It is is unequivocal. There are a whole range of data that show this. There are ocean measurements, decreases in snow cover, reductions in Arctic sea ice, balloon measurements, boreholes and satellites that all show data entirely in-line with that obtained from from surface weather stations.
The urban heat island effect does in fact exist but in reality it is small. This has been studied taken into account in the calculations There is work that has been done by NASA , for example, which uses data from weather stations in rural areas and this shows the same warming
The Research has also clearly demonstrated that analysis of long-term global temperature rise for days that are windy and those that are calm shows no difference at all.. If there were any significant influence from the urban heat island effect, it would expected that there would be more warming on see more warming on calm days when the heat would be retained more in the cities..
Additionally the global pattern of warming does not coincide with the occurrence of cities. The greatest warming has been found in the Arctic and the high latitudes of the north. Research has shown warming on a planetary scale of 0.8C since the year 1900 and more than half of this happened after 1979.