Why is it colder in March than September?

This is a question that I received not too long ago. I think it is an interesting topic. Hopefully, you enjoy:

"I believe that I understand the concept that the sun is the cause of the seasons, and how longer days cause our summers. You often mention about how strong the sun is and that the sun is as strong in March as it is in September, but that doesn’t quite make sense to me. If the sun is strong enough to cause the average temperatures to rise in March, then how is it weak enough for the averages to drop in September?"

I applaud questions like this because it means that the things I say are inspiring complex thought. You are correct that the sun is the cause of the seasons, but it is not just simply the amount of sunlight that causes the seasons. If you think about it, the North Pole gets a lot more hours sunshine in the summer than Miami does. Why is it then warmer with less sun in Florida? It has to do with the angle of the incoming energy from the sun. The sun is much higher in the sky over tropical areas, and when the sun is higher in the sky, two things happen to allow it to better heat the ground. The first is that the sun is more concentrated when it strikes the ground. You can experiment with a flashlight in a dark room to see how this works. A flashlight pointing straight at the wall will have a brighter and tighter spot, but a beam that is more angled will have a fainter and more spread out lit area. The second thing that happens to a lower sun is the fact that the sunlight must pass through a larger slice of the atmosphere. The air molecules then scatter the energy in all directions and less actually makes it to the ground.

But I have avoided the true answer to why March and September differ. The best way to answer this question is to review the processes of heating and cooling. At all times there is a two way process to cause a change in temperature. It is easy to comprehend the fact that when we add heat energy to an object, its temperature rises. Though what many people don’t realize is that all objects that have a temperature are constantly radiating energy away from that object. The amount of energy being radiated, or lost, from an object is dependent on the temperature of an object. For that object to warm, it must gain more energy than it losses through this radiation. To better explain, let’s use an example of two bricks; one brick is at a temperature of 50 degrees and the other at 90 degrees. Because the second brick is hotter, it is radiating energy at a faster rate than the cooler one. Therefore, if we wanted to warm each brick an additional 5 degrees, the hotter brick needs more energy to make this happen than the cooler one.

If we understand the example of the bricks, we can then apply this to the question at hand. In March, our part of the planet is colder than it is in September. Therefore, the ground needs less energy to warm in March than it would in September. While the same energy coming in from the sun is enough to cause the temperature to rise in March, we are still losing more than we gain in September. The resultant is the cause of the rising average temperatures in March while averages fall in September. This answer also stresses how hard it is to get extreme heat. When temperatures reach into the 100s, it requires a tremendous amount of energy to get even a little more rise.