Final answer:
The thermosphere feels cold because there are fewer air molecules to transfer heat energy to our skin. The high kinetic energy of these individual molecules does not translate to warmth without sufficient density for collisions, despite what would be considered high temperatures in this part of the atmosphere. The natural greenhouse effect influences the distribution of temperature across different atmospheric layers, keeping the lower layers warmer.
Step-by-step explanation:
The thermosphere feels cold to our skin because the air is very thin at that altitude, which means there are far fewer molecules to transfer heat energy to a person's body. In the thermosphere, despite the individual molecules having high energies (as they absorb ultraviolet and solar radiation), the density of particles is so low that the total heat is not enough to warm our skin, hence it would feel cold. Moreover, conventional definitions of temperature are based on the average kinetic energy of molecules. In the thermosphere, although these few molecules are moving very fast (which means high kinetic energy and temperature), they are unlikely to collide with us or each other, resulting in little heat transfer.
Another factor to consider is that temperature sensors, and by extension our skin, rely on the number of particles colliding with them to measure temperature. In the thin atmospheric layers such as the thermosphere, the normally high kinetic energy (high temperatures) of the molecules does not equate to the same kind of warmth we would feel at the Earth's surface because of the lack of substantial air pressure and density.
The natural greenhouse effect also plays a role in maintaining the temperature of the atmosphere. Without the presence of greenhouse gases trapping heat, the thermosphere would be even colder, as the lower layers of the atmosphere are kept warm while upper layers remain cold due to less heat being trapped.