As I understand it, comparatives compare with something. So something that is colder is more cold than another thing. However, can't a word like colder be used as an adjective without being compared to something else? For example, is it ungrammatical to say the following?
People who live in colder climates should be careful about their heating bills.
The adjective cold could be inserted in place of colder, but I think the meaning would be different. To me colder sounds like 'somewhat cold' as opposed to 'absolute cold.'
So my questions are as follows:
1. Is this use of colder grammatical?
2. If so, is it still considered a comparative?
3. Do you agree with my understanding of colder vs. cold in the example?