Aerobic Interval Training

To loose fat you have to increase the intensity of your workout. If you are getting on the treadmill, or elliptical trainer, or whatever you use for aerobic work and you are able to read or hold a conversation while you are doing it then you are not working hard enough.
To get the best results from purely aerobic exercise you need to be doing intervals. (You will get better results with high intensity anaerobic exercise.) That means that you must exercise as intensely as possible for a short period then slow down for a period of active recovery. You can spend less time exercising and get the results that you want.
An interval workout will look something like this:

5 minute warm up
20 minute intervals
20-30 second sprint
60-90 second recovery
5 minute cool down

30 minutes of intervals will get you better results than 60 minutes of regular cardio. (60% of max heart rate, or being able to hold a conversation while exercising) When you exercise at high intensity you increase your metabolic rate. You actually burn fewer calories during your exercise session but continue to burn calories at an elevated rate after you are done exercising. There is also some evidence that high intensity exercise helps the body break down fat, a benefit that lower intensity exercise does not have.