It is important to be comfortable at work, especially when the weather turns really hot, as it is hard to concentrate on your work if you are hot and sweaty and feel uncomfortable.
I think it is fine and totally acceptable to wear short sleeve shirts in the office, and for women to wear sleeveless tops. As long is it smart looking and doesn’t cross the boundaries and start becoming more like beachwear, then it should be acceptable for employees to dress according to the heat.
Customers or visitors to an office understand that it is hot, and would not expect someone to be dressed in clothing that is not suitable for the weather conditions. I’ve always found it very strange to see a man in wearing a suit in extremely hot weather when it is clearly making him uncomfortable. Why should we feel as if suits are a must no matter what the temperature.
A short sleeved shirt can be worn under a suit jacket just the same as a long sleeve shirt, then the suit jacket should be removed when the temperature gets too hot without the employee feeling as if he is not smart enough for the office.