気温 and 温度: air temperature and object temperature
Identify what is measured and keep temperature comparisons separate.
Air temperature
気温 (きおん) means air temperature. 「朝の気温は十度でした」 says the morning air temperature was ten degrees.
「昨日より気温が下がりました」 says the air temperature fell compared with yesterday. It gives no exact size of the decrease.
Temperature of various things
温度 (おんど) is the broader word temperature. 「お湯の温度を測りました」 means measuring the hot water's temperature.
「温度を少し上げました」 says the temperature was raised a little. Context identifies which device or substance is meant.
Keeping measurement targets separate
「気温は低いですが、水の温度は高いです」 says air temperature is low while water temperature is high. They concern different measured things.
「気温が上がる予報です」 forecasts a rise in air temperature. Distinguish it from an observation that it has already risen.
Can 「お湯の温度」 be replaced by 気温 without changing the meaning?
Show the answer and why
No. Water temperature and air temperature have different measurement targets.