These may not be warts but seborrheic keratoses. These are benign growths that can be removed by various means. You have to see a board certified dermatologist to diagnose and treat these.

Have them evaluated as there are several types of wartlike lesions that can occur. They may be treated with a variety of different methods including topical treatment, freezing, or acid treatments.

Normally warts do not develop spontaneously on the back. Perhaps it is a sborrheic keratosis? Please see your dermatologist

Thanks Kim Ross MD

They may not be warts; may be seborrhic keratosis. See a Derm.

There are many options to treat your warts. You can try over-the-counter products like Compound W. If this does not work you can visit your dermatologist who may offer a prescription, treat with liquid nitrogen, offer to remove them surgically, or by other methods.