Because your building's HVAC was designed for empty offices.
A quiet tower fan or a small ceramic heater under your desk is the difference between working and suffering. Look for anything under 50 dB and a tip-over shutoff.
Not a fan — a room circulator. Moves air across the whole room instead of blasting your face (and mic). Whisper-quiet on low, five-year warranty, check current warranty terms before buying.
Warms the whole room instead of just roasting your shins. Tip-over shutoff and auto-off timer make it safe to run under a desk. Cheaper to run than turning the whole house up.