The climate of Japan is milder than that of Engalnd.の文で、同じものではなく同種類のものは代名詞 one で表すと習った記憶があるのですが、なぜこの場合that なんですか？例えば I do not like this red shirt. I would like a blue one. のようにです。教えてください。

Hi

Let’s look at "red shirt", "climate of Japan", "Japanese climate" and "Japan’s climate" together:

I do not like the red shirt. I prefer the blue one.
I do not like the climate of Japan. I prefer that of England.
I do not like the Japanese climate. I prefer the English one.
I do not like Japan’s climate. I prefer England’s.

I do not like the ADJ NOUN. I prefer the ADJ PRO.
I do not like the NOUN of NOUN. I prefer PRO of NOUN.
I do not like the ADJ NOUN. I prefer the ADJ PRO.
I do not like NOUN’s NOUN. I prefer NOUN’s (NOUN).

You can see here that you "red shirt" example and "the climate of Japan" are significantly different. One is possessive, the other is a noun phrase (functionally a noun). If you used "the Japanese climate" you could then use "the English one", because these are both of the form ADJ NOUN.

Good luck!

z. 　

ありがとうございました。