(i) At higher latitudes, the rays of the Sun fall in an oblique way. Oblique rays not only travel a longer distance, but also heat a larger area. Thus, they have less heating power. Hence, with higher latitudes, the temperature goes on decreasing.
(ii) The vertical rays of the Sun give more insolation than the slanting rays because vertical rays travel a shorter distance and heat up a smaller surface area leading to higher temperatures whereas slanting rays not only travel a longer distance, but also heat a larger area. Thus, they have less heating power.
(iii) Hot deserts have no cloud cover, which allows high insolation during the day and rapid loss of heat due to terrestrial radiation at night resulting in high range of temperature. On the other hand, forests absorb 90% insolation and the solar energy absorbed by plants is used in the process of transpiration resulting in low range of temperature.