I hate to say it, but you're showing the classic symptoms of carpal tunnel syndrome. I know about it, I have it, and cycling is one of those things known to aggravate it. I was having the same type of trouble with mine riding today. What the others have been telling you regarding changing hand position, keeping from putting too much weight on them, etc. are all real good ideas, but it might help to know the mechanics of how the nerve in the wrist gets compressed to cause the numbness, and avoid getting your wrists in these positions whenever possible.
Basically, if your hand flexes back too much (the classic stiff arm position in football), or bent inward too much you compress the carpal tunnel in your wrist and put pressure on the nerve to the hand. Try keeping your hand in a neutral position, with the back of your hand just slightly bent back, by maybe 15* or so, so that your thumb is more or less lined up with your wrist when viewed from the side. Flexing your fingers periodically while you ride is also a good idea, as is not tightening your grip on the bars.
Also, and this may seem kind of obvious, make sure the gloves aren't tightened down too much at the wrists, which will cut off circulation and contribute to swelling and pressure on the nerve. You may need to loosen them after you've been riding for a while.
If you're having too much trouble with numbness, you might try riding without the gloves for awhile and see if that helps. Sometimes it works for me.
You might want to get checked out by a doc, or at least look around the web. There are exercises you can do to ease the symptoms...but not while you're riding.