When it is cold you do not do as much exercise or go out the house because of the dark night so you may need more insulin and vice versa in the summer. If you go abroad were it is really hot then insulin tends to work quicker which means you need to reduced the amount you take. I have always had a problem when the season change i will have a week of BS been all over then they go back to normal again, many consultants have tried to work it out but cannot find out why so i just leave it till it goes back to normal.