A heat budget is the perfect balance between incoming heat absorbed by earth and outgoing heat escaping it in the form of radiation. If the balance is disturbed, then earth would get progressively warmer or cooler with each passing year.

The average temperature of the earth remains rather constant. It has been possible because whatever the amount of heat the earth receives from the sun in the form of short-waves, it radiates back to the atmosphere in the form of long waves. There exists a stage of heat balance or equilibrium between the earth and its atmosphere. This balance of heat is termed as the earth\’s heat budget.