The variations in elevation, slope and aspect of the Commons create numerous microclimates and give rise to differences in vegetation.

The Commons are high up and exposed. At about 200 metres above sea level, they are strongly affected by the wind and the sun, but the effects of this depend on where you are. There are many hollows on the plateau surface, and the edges of both Commons twist and turn to face south one minute and north the next. Consequently, sunlight, wind speed, rainfall amounts, evaporation and run-off rates can all vary dramatically within a short distance.

Some south-facing slopes, clear of woodland shelter, can be intensely warm in spring and summer. The plant and insect variety this stimulates is spectacular. Small hollows from earlier quarrying can produce similar effects, though in autumn and winter cold air tends to be retained in the hollows ensuring a relatively low temperature.

Dew ponds on the plateau surface also create highly localised differences in humidity, air movement and temperatures. Their use by grazing cattle can affect soil quality and plant growth.