Your problem seems to be related to something else, but I'll make a stab at answering the question: can it be calibrated?
Any sensor can be calibrated with the right equipment and a wee bit of coding. These range from single point calibrations, simply applying an offset to the reported value, to full, multi-point, linearized calibrations.
The standard calibration we do in our lab involves the use of a NIST traceable reference with an established uncertainty of measurement modeled on BIPM's GUM. (I had links to guides here but SO doesn't think me worthy of sharing them, you'll just have to google them)
Adafruit made a great wee guide for makers on calibration here, though it seems from reading this thread that achieving accurate results from the Sense Hat might take some work. I probably wouldn't mount the hat directly to the Pi's GPIO if you need accurate readings of ambient air.