It is necessary to have a fan schroud on a 2000 ford explorer

In cold weather probably not, but in mild to warm weather yes, it really helps the fan draw the air pass the radiator. Guess if you see your temp gauge climbing into the red zone, you'll know why.

okay thank you. That helps me out a lot.

I say absolutely yes. Just think how much money manufactures would save if they eliminated shrouds on all the models... millions! Believe me, if the engine could do without it, it wouldn't be there.