text: Climate realists are generally willing to assume, for the sake of argument, that the Earth has warmed somewhat in recent decades. In fact, though, it is not obvious that even this modest claim is true. Satellite data show no net warming for as long as such data have been collected, i.e., back to 1979. Ocean measurements show no net warming over that period, either; the evidence for warming is based on land measurements. But the accuracy of land measurements depends on proper siting and maintenance of weather stations. One obvious factor is the urban heat island effect: many weather stations are located in cities, which grow warmer as more people and buildings accumulate. Thus, increasing temperatures at such stations may be measuring urban development rather than the climate. We all know that the urban heat island effect is realchance of frost in outlying areasyet the data that alarmists rely upon do not take it into account.