In reality, you'd want an outward force a full order of magnitude higher than the cargo capacity.
The number of people talking about the issue of balancing the elevator makes me think perhaps I have misunderstood. I figure I'd probably put a counterweight mass on a climber above geostationary. Geostationary is where things balance, right? The mass above geostationary (at angular velocity of 360 deg / day) wants to fly away, and it holds up the ribbon. Want to put a heavy load on the ribbon bottom? Send a signal to have the counterweight climb further up (which, past geostationary, feels like down to it, right?), increasing the amount it pulls up. Perhaps the distance necessary to apply this effect is substantial, but heck we're already going to geostationary, right?
And from a message further up:
The base could easily be placed on a barge in the middle of the ocean. In fact, that's just about ideal; it can move around relatively easily...
Well, you've basically got a pendulum that is 35,000+ Km long. That's going to be a pretty long period to make it do anything, I bet. Maybe easier would be to just detach it from your barge and roll it up into the sky at the balance point if you need to get out of the way of some terrestrial event.