It is expected that as the temperature goes up by the above method, frozen carbon dioxide will defrost and evaporate into the atmosphere, raising temperatures even more. Why would this be

CO2 is a green house gas

Explanation:

CO2 is believed to act as a canopy over the earth's surface absorbing infrared (heat ray) from the earth and re-emitting it  back to the earth.

By so doing, temperature is increased and more frozen CO2 will defrost causing even greater temperature rise.

The gradual rise in the earth's temperature is known as global warming.