# Understanding a diagram of Earth's radiation balance

Trying to understand this image. Can someone tell me if I have the right reasoning here:

• Sun has 100% SW shooting to earth

• 30% of that 100% is reflected by clouds

• 70% remains
• Of that 70%, 45% of that SW is absorbed by Earth's surface.
• That leaves 25%, where does that go/factored into?

The entire right half of this diagram confuses me, what is happening there? Why is there a red line connecting 70%SW and 70%LW? What does "??%LW" mean?

Thank you

• sw is short wave radiation and lw is longwave radiation(infrared or heat radiation) Mar 14, 2018 at 18:53
• @trondhansen Thanks. I understood that part. And I know that Earth emits long-wave radiation (for some unknown reason) and the Sun emits short-wave radiation (for some unknown reason). So with the two we have to work out how the energy that Earth naturally emits and the energy that comes into Earth is balanced out. So everything SW is by the Sun, and everything LW is from Earth? What does 70%SW and 70%LW and ??%LW and the red line connecting the two mean?
– yre
Mar 14, 2018 at 18:57
• What happens to that 25-35% that doesn't make it to the surface?
– yre
Mar 14, 2018 at 19:01
• it gets reflected back to space before it reaches the planet. Mar 14, 2018 at 19:03
• Can't say I've ever dug into the details fully... but know sun emits primarily shortwave and the Earth longwave because $f_{max} \propto T$ as shown in Wien's Law (looks like Wikipedia has some quick explanation of how he made the proof of that)... which then also results out from the larger Planck's Law (once again the Wikipedia article discusses it's derivation). If looking for more simple conceptual understanding, it might be a good separate question! Mar 14, 2018 at 20:00