How does sunlight change the balance of nature?

Answer 1

The air above us is relatively transparent to visible radiation, allowing the bulk of the Sun's energy to reach the Earth's lower atmosphere and surface. Fortunately, the atmosphere is opaque to almost all solar radiation in the UV, shielding the biosphere from these potentially harmful rays.

The Earth receives most of its direct heat from the visible and near- infrared spectrum of sunlight, retaining about 70 percent of what pours down on its day-lit hemisphere. The rest is returned, by reflection, back into the cold of space. A part of what the ground and oceans and lower atmosphere absorb also leaks outward through the atmosphere in the form of infrared radiation. The remaining fraction--trapped in part by greenhouse gases--sustains the habitable environment to which we are accustomed. Any variation in total radiation from the Sun will force an accompanying change in mean-surface temperature.

Solar UV radiation, unlike that in the visible and infrared spectrum, seldom reaches the surface of the Earth since it is absorbed by the atmosphere. In addition, a steady stream of energetic particles and magnetic fields (the solar wind) flow continuously outward from the Sun, impacting and deforming the Earth's extended magnetic field. These upper reaches of the atmosphere are influenced strongly by the flow of particles and solar UV radiation. The changes that they feel can potentially affect the climate, through various connections to the lower atmosphere and surface of the Earth. As an example, variations in the flow of both UV radiation and atomic particles that accompany changes in overall solar activity alter the amount of ozone in the stratosphere. Since ozone in turn affects the lower atmosphere and biosphere, it provides another possible connection between solar variability and the climate system.