Actually, the heat is more dangerous than the cold. In the U.S., most airlines wont ship animals during the summer months. You'll have to look up Sweden's rules for accepting a dog from another country to see what immunizations and such is required. You'll also have to research what the airline requirements are in terms of the type of kennel he can be shipped in. Most airlines (in the US at least) also require a certificate of health from a vet. Last year we moved my husband's dog from England (where they were living) to the U.S.. It was a bit of a pain, and requires some planning.