# Why is the part of the earth tilted towards the sun warmer? Which factors matter more?

The part of the earth tilted towards the sun is warmer. For example, in the Northern hemisphere, the earth is tilted towards the sun in the months around June and tilted away from it in the months around December.

• This has the effect of increasing the exposure of the earth to the sun for the latitudes tilted towards the sun.
• Also, the more tropical the latitude, the more energy is received per unit area.

These two ideas are illustrated by the figure below:

There are other effects, too...

• If the sun's energy must pass through more atmosphere, there is greater opportunity for it to scatter into space before reaching the earth
• When the sun strikes the earth, if it strikes it obliquely there is greater chance for the light to be reflected rather than absorbed.
• Finally, whether the sun strikes water or land or ice has an effect, because each has a different degree of absorption and reflectivity.

In total there seem to be 5 different major factors in how much energy is absorbed by the earth from the sun.

My question is what is the relative importance of each of these factors? Is there a set of equations or measurements that describe the total energy received by the sun in terms of these 5 different factors?

• Are you looking for the radiative transfer equation?
– gerrit
Commented May 3, 2017 at 14:07
• It has nothing to do with distance it has everything to do with angle (because it changes the density of the incoming light), and the length of time during the day it gets sun, the distance to the sun changes by far more than tilt with no effect.
– John
Commented May 4, 2017 at 15:54
• You overlooked the fact that there is also longer daytime duration in the summer Hemisphere. When you consider how much of this map is covered, it's a significantly larger percentage in the summer hemisphere (you can adjust the date!). I don't know equations to compare the factors offhand, but an interesting question, and hopefully I or someone will give you a more thorough answer :-) Commented Jun 9, 2017 at 9:29

The 5 factors you mention are not nearly as important to the effect you're asking about as another, more fundamental factor: time.

If you've read my answer to this other question, you should understand that all of the factors you mention would create temperature differences at different latitudes whether the Earth is tilted on its axis or not.

But because the Earth's axis is tilted, at some parts of the year the regions of the Earth tilted towards the Sun (in "summer") receive sunlight a greater proportion of the day than the regions pointed away (in "winter").

Not only that, because of the more direct angle of the Sun the factors you list mean that the regions in "summer" are heated better during the day than the regions in "winter". And this adds up over all the days of summer or winter until the Earth's orbit reorients the axis relative to the Sun.

Or even more succinctly, summer is hotter because the Sun is higher in the sky for more of the day.