Winnie's description is right, but one thing she misunderstood is that 기온 is used to express mood. What she wanted to say must be 기운. e.g. 기운이 없다. Plus, 온도 and 기온 can be used interchangeably in most cases.

온도:temperature ,it's express we can feel it. High or low/...온도 높다/낮다/ 기온:air temperature emphasizes air temperature meanwhile you can use 기온to express mood,기온이 없다:bad mood/low spirits/no strength