I have read that temperatures can reach 4,000 degrees high up in the atmosphere. It that possible?
It’s true. In some portions of the ionosphere, a layer extending from about 60 to 500 miles above the Earth’s surface, temperatures that high exist. But that incredibly high “temperature” is not a temperature in the sense that we perceive it. It is a temperature based on the kinetic energy of gas molecules and free electrons and ions that are “heated” to rapid movement by bombardment from high-energy particles arriving from space and by short-wave energy from the sun. So few molecules and other particles exist at that great height that the total amount of energy there is minimal by surface standards. The concepts of “heat” and “temperature” are meaningless in an atmosphere so rarefied that it is a near vacuum.