It is generally accepted that THE CLIMATE OF LONDON, first published in 1818, contains the first reference to the urban effect on the local climate. CLIMATE is a general treatise on the field of climatology and is largely based upon measurements and observations made by Howard. A second edition, published in 1833, comprises three volumes. The first presents observations on aspects of climate (temperature, pressure, wind, humidity, evaporation, rain, etc.), while the other two provide tables and notes gathered by Howard over a thirty-year period. Together they illustrate the beginnings of a science of the weather and climate. While Howard is justly famous for his classification of clouds, CLIMATE illustrates his innate scientific approach in other areas; an approach that relies on careful observation and experimentation as a means of evaluating competing theories and the use of graphics to display results.

His analysis of temperature records gathered in the city with those obtained in the city environs is of particular interest to urban climatologists. He concludes that the “Mean Temperature of the Climate [of the London area], …is strictly about 48.50° Fahr.: but in the denser parts of the metropolis, the heat is raised, by the effect of the population and fires, to 50.50°; and it must be proportionately affected in the suburban parts. The excess of the Temperature of the city varies through the year, being least in spring, and greatest in winter; and it belongs, in strictness, to the nights; which average three degrees and seven-tenths warmer than in the country; while the heat of the day, owing without doubt to the interception of a portion of the solar rays by a veil of smoke, falls, on a mean of years, about a third of a degree short of that in the open plain.” In hypothesizing the cause of this urban ‘heat island', as it became known, Howard identified four causes for the observed differences in air temperature:

1. Anthropogenic sources of heat resulting in atmospheric warming, particularly in winter,

2. The geometry of urban surfaces that ‘traps' radiation and obstructs ‘free radiation to the sky',

3. The effect of urban ‘roughness' in impeding the passage of ‘the light winds of summer', and

4. The availability of moisture for evaporation in the country.

Unfortunately he had no instrumental means for evaluating the magnitude of these contributions however, he had identified virtually all of the factors that are responsible for the UHI – that he did so in 1818, at the very beginning of the scientific study of weather and climate is remarkable. In this paper, I will summarize Howard's work and draw parallels with that of Oke in terms of singularity of purpose, methodological rigour, clarity of presentation and sustained scientific engagement.