[Using an enclosure caused warping issues]

I recently completed building an enclosure for my 3D printer and now every print has major warping issues. When the printer was sitting out in the open, in my living room, I rarely had issues with warping. The warping gets worse as the infill density increases. One model of about 100 layers and 50mm x 25mm printed fine until the last few layers and then it warped. I have tried:

• increasing the bed temp from 60C to 65C
• using a glue stick
• Slowing the initial layer print speed to 25mm/s

 

I understand the reasons for warping of parts in general, but why do I have such a huge problem now that I am using an enclosure?