Comparing "qihou", "qiwen", and "tianqi"

气候, 气温, and 天气 are similar in the fact that all are nouns that related to meteorology. Yet, they are very different in all other regards and cannot be used interchangeably. A first difference is 气候 and 气温 are used in formal situations, while 天气 is used in informal situations. And the biggest difference is the words simply have different meanings as 气候 is climate, 气温 is air temperature, and 天气 is the weather in the general sense.

气候 (qìhòu) 气温 (qìwēn) 天气 (tiānqì)
Meaning climate air temperature the weather
Part of Speech noun noun noun
Formality formal formal flexible

Sources and further reading