I am having a similar problem although only to about 85 degrees, the best solution is to vent the closet outdoors if possible. I am installing an inexpensive through-the-wall exhaust fan, and another small fan pulling air in from my bottom vent.

Even if you can't modify the walls, more/cooler airflow is the answer. As someone said above, your plants will either die or simply stop developing because photosynthesis slows/stops over 90 while the plant just tries to transpire as much water as possible.

Good luck.