I suppose there is a speck of truth that weather affects the mood of people. In my country, we have four seasons, thanks to its location. And...change is obvious. During summer people look more relaxed, cheerful, open to communications, and the mood is overall quite high
. While in winter people try to stay home, and go out not so often with certain regret that they have to leave their nice and warm rooms.
My opinion is that not really the temperature affects us, because you can put more clothes on, or off, according to your needs. But what really influences our behaviour is the changing colours of the environment. It's said that different colours arise different feeling in us, I suppose you have heard that. And in countries where it's hot, there are more bright colours..like yellow, orange, green, blue. These ones symbolise happiness and...joy..also serenity I think. While the cold climate's colours are mainly grey, brown, black...they are not really positive ones, and charge you with negative energy
If I am not wrong, I think that Feng Shui deals a lot with this kind of reaction in people.