Let’s consider how incoming radiation affects the overall radiation balance of the Earth. Open the Planetary Climates learning tool and navigate to the 'Build A Planet' learning tool by clicking 'Go To' at the top and then 'Build A Planet'. Enter the following conditions to create Earth (you can click on the input boxes to manually enter a number):

Notice that the two centre bars are now balanced: incoming radiation is equal to outgoing radiation. The “Energy in” bar refers to radiation that is absorbed by the earth’s surface. Which two factors affect the "Energy In " bar?

Question: What would the earth's temperature be if the planet was double its current distance from the sun?

Once again, open the Planetary Climates learning tool, navigate to the 'Build A Planet' learning tool, and begin by creating Earth's conditions (as described above). Then change the 'Distance from Sun' slider from 1 AU to 2 AU as shown on the right.

Changing the Earth's distance from the sun causes an imbalance in the energy bars. There is less energy entering the earth’s atmosphere than exiting. To create a new radiation balance, change the surface temperature. What is the new temperature?

When the earth is twice as far away from the sun, the new surface temperature is -69°C.

Question: What would the Earth's temperature be if the planet was half its current distance from the sun (0.5 AUs)?