Light in a vacuum travels at c, light slows down passing through a medium because the medium resists /opposes the lights travel .
The Earths atmosphere is a medium , it opposes the lights travel . At altitude the atmosphere is less dense therefore it has less resistance .
The answer is yes !
Heat is a product of atmospheric resistance and that is why a fire does not burn in a vacuum because there is no atmospheric resistance .
But anyway , the earth is losing atmosphere into space and by removing the green houses gases we have even less atmospheric resistance .
This allows for light to travel faster to the surface of the earth from the sun and has speeded up the process of light propagation that is creating the heat .
The suns incident rays current in space is cold , it only becomes heated when there is current resistance and/or an inverted current . I.e The ground gets heated and then creates a current the opposite direction to the incident current creating denser propagation (heat) .
Without atmosphere there is no heat , the atmosphere propagates the light .
This is a world emergency post by the way , you really should try to understand .