CLIMATE CHANGE - PART 1: THE ALBEDO

This is the first of posts dedicated to describe the main factors driving the warming and climate changes of the Earth. I wull start with the most intuitive of all: the albedo. The Earth and its atmosphere intercept the solar electromagnetic radiation (this radiation “transports” heat and the visible light is only a part of it) and reflect a fraction, called albedo, in the outer space. The Earth becomes colder if the albedo increases, since the quantity of absorbed radiation decreases. Viceversa, the Earth become warming if the albedo decreases: indeed, the absorbed solar radiation increases. In summary: the Earth become cooler if the albedo increases while the Earth become warmer if the albedo decreases. Let’s analyse some natural causes and after let see how the man actions can change the albedo, with consequences on the terrestial temperature and clime.
The snow reflects almost all the solar radiation. Therefore, when the snow melt the albedo decreases and, as a consequence, the temperature increases (remember that when the albedo decreases the temperature increases). The increase of temperature causes the melting of other snow, with further temperature increases. This phenomenon continues until termodynamic equilibrium is reached, but the consequence is an overall increase of the temperature and a further glacier melting. On the contrary, the clouds reflect the solar radiation, contributing to globally increase the albed and to cool the Earth. The aerosols (the particles in the atmposhere caused by natural events, like the volcan eruptions and the sandstorms, or by the man caused pollution) reflect the solar radation, increasing the albedo, also if the reflective power changes as function of it composition.
The antropogenic (i.e. due to the mankind) activities of disforest and agricolture can decrease the albed and, therefore, increase the global temperature. For instance, the trees of the tropical forests are cut and replaced by more black soil for cultivation purposes. In this case, the absorbed solar radiation increases (the darkest colors absorb it while the white reflect the solar radiation) and the temperature increases. The bad management and disforest of lands can contribute to the terrestrial temperature increases. Some satellite images show the city areas with dark building colour are hotter than city areas with gardes and trees, as for the dark soil of the forest. Therefore, the urbanistic policy and the architectural choices can influence the Earth warming. In the next post, I will discuss of this topic: the Urban Islands of Heat.