If there was no carbon dioxide in the atmosphere, the temperature on earth' surface would be

The greenhouse effect is a naturally occurring phenomenon that is responsible for heating of Earth’s surface and atmosphere. Carbon dioxide and methane are commonly known as greenhouse gases because they are responsible for the greenhouse effect. Without greenhouse effect the average temperature at surface of Earth would have been a chilly $-{18}^{\mathrm{o}}\mathrm{C}$ rather than the present average of ${15}^{\mathrm{o}}\mathrm{C}$. So, it would be much lesser without ${\mathrm{CO}}_2$.