Summer weather itself is bad enough, but the plant I work in has areas that can get up to 140F (60C) in the summer - we have special cooling vests for working in those areas, and people can still only work 15-20 minutes at a time before having to cool down. If I have to be in one of these areas, it's really miserable in a diaper - and the cooling vests do nothing for sweating in my diaper area.
Fortunately, the majority of my work is in an air conditioned office. We keep the thermostat at 72 degrees Fahrenheit (22C), and I keep a hoodie handy because I get too cold.
I went several years with my on-again, off-again incontinence flaring up in June or July, and it was always frustrating that I had to wear diapers during the hottest months. Now, I'm in the longest stretch I've ever had of incontinence (7 months - not that long compared with some folks here, but still longer than I've had) and I don't know if I'll ever get another period of time where I don't need diapers.