Answer :
Final answer:
The average surface temperature of the Earth is 15 degrees Celsius due to the greenhouse effect caused by greenhouse gases. Without these gases, the temperature would be much colder, about -18 degrees Celsius.
Explanation:
The average surface temperature of the Earth is 15 degrees Celsius because of the greenhouse effect. The greenhouse effect is caused by greenhouse gases like water vapor and carbon dioxide, which trap heat in the atmosphere. Without these greenhouse gases, the average surface temperature of the Earth would be much colder, about -18 degrees Celsius. This is due to the fact that the greenhouse effect prevents most radiation from escaping directly to space, keeping the planet warm.
