Since you have a turbo, your brake pads could be a higher performance variety and not work as well when cold. The brake booster check valve could be affected by the cold and not giving full boost. There could be ice in the brake lines. Do you know if the brake fluid was changed within the past two years? It is a regular maintenance item for Volvos. Just some ideas to kick around.

Cold weather makes everything grumpy. In Maine the cold is a fact of life, and I just accept the fact that stuff doesn't work right until it warms up. At -20 the seats feel like boards. At -30 the starter seems to say "no-way. no-way. no-way." You are in the sunny south. Count your blessings.

My '81 240 did this for years...not sure what it was...maybe some moisture in the fluid, but it was changed regularly. Seemed to go away after I changed the master cyl.

It could be (frozen)condensation on the brakes. I like to pump the brakes when I first start out in the morning. That usually clears out anything that might have frozen on the rotors at night. I am not a scientist, but I think that the rotors pull the moisture at night to cool off when you stop and tur off the car. Someone might have a better answer as to why it happens. I really don't have a problem in the morning. I do hear a slight grinding noise in the morning when I brake and I account that to condensation and slight rust on the rotors. Try pumping the brakes when you fist start out and see if that makes a difference.....