In autumn it is colde/more colder than in summer?

In autumn it is colder than in summer. - Осенью холоднее, чем летом.

Adjective has three degrees of comparison. They are Positive, Comparative and Superlative. There are two ways of formation these degrees. We form these degrees with suffixes and with words. We use the suffixes when adjectives have one or two syllables. When adjectives have more syllables, we use words more for Comparative degree and the most for Superlative degree. Cold has one syllable and degrees are formed with the suffixes - er for Comparative degree and the - est for Superlative degree. Cold - colder - the coldest. We use Comparative degree with than.