COD: Black Ops 2 Increase Difficulty in Campaign?

[undertaker2k8]

Accidentally lowered the difficulty level in Black Ops2 , now it seems that there is no way to increase it short of starting a new campaign or playing in individual mission mode? Any ideas?

In BF3 you could not change it at all during campaign, but it seems weird that you can decrease it but not increase in Black Op2...