Colder air is more dense and aero drag is directly proportional to density. So aero drag increases proportionally with a drop in temperature. But the effect isn't huge - for example, you'll get about 12% more aero drag bicycling at 32-deg (F) than you would at 75-deg. If you're also bicycling into a headwind then a temperature drop will amplify the affect of the headwind - for example, if the the headwind causes X drag at 75, then it will cause 1.12X drag at 32. I don't know if this is the "multiplied effect" you refer to.

- Mark