2.1: Factors affecting the Climate

Latitude and Angle of Insolation

The latitude of a location plays a major role in determining the region's climate. The farther you are from the Equator, the higher your latitude. Figure \(\PageIndex{1}\) displays lines of latitude on Earth for the Northern Hemisphere.

Figure \(\PageIndex{1}\): Latitudes increase from 0° at the Equator to 90° at the north pole and decrease to -90° at the south pole. (Public Domain; Gregors via Wikimedia Commons). Alternative description of the image.

Your latitude determines the angle of incoming sunlight, which is known as the angle of insolation. A higher angle (closer to 90° or directly overhead) concentrates solar energy into a smaller area, resulting in higher, hotter temperatures, while a lower, oblique angle spreads energy over a larger area, resulting in lower temperatures. To demonstrate the importance of the angle of insolation, let's conduct the following experiment: Using a flashlight and in a dark room, hold the flashlight so that the light is directly over the ground, as shown in Figure \(\PageIndex{2}\). Then, tilt the flashlight so it is low on the horizon, as shown in Figure \(\PageIndex{3}\).

Figure \(\PageIndex{2}\): When the flashlight is directly over the surface, the energy is concentrated. (CC BY 4.0; Alicia Mullens)

Figure \(\PageIndex{3}\): When the flashlight is angled over the surface, the energy is more diffuse. (CC BY 4.0; Alicia Mullens)

4. When the flashlight is shining directly above the surface (Figure \(\PageIndex{2}\)), the area illuminated on the surface is:
   1. a small, bright circle
   2. a large, dim area

5. When you lower the flashlight on the horizon (Figure \(\PageIndex{3}\)). The area illuminated on the surface becomes:
   1. smaller and brighter
   2. larger and dimmer
   3. it doesn’t change

6. Now let’s apply this to sunlight. Sunlight would be most intense when:
   1. The Sun is directly overhead
   2. The Sun is lower on the horizon

We can also apply these conclusions to sunlight and how its intensity changes throughout the day as the sun rises and sets with low angles of insolation, but has a higher angle around noon. Thus, when the sun is high in the sky, the incoming sunlight is more intense, whereas when the sun is low on the horizon, it is less intense. Now, let’s examine how this would relate to latitude. There are a few things to note here. If the Earth were not tilted, the sun would be directly overhead year-round, and the overall set-up of incoming sunlight would appear as shown in Figure \(\PageIndex{4}\).

Figure \(\PageIndex{4}\): Sunlight over the Equator (low latitude) vs. sunlight near the poles (high latitude). The Sun is directly over the Equator. (CC BY 4.0; Alicia Mullens). Alternative description of the image.

7. Based on Figure \(\PageIndex{4}\), a beam of sunlight covers a _______ area over higher latitudes than near the Equator.
   1. smaller
   2. larger

8. As a result, sunlight at higher latitudes would be ______ than near the Equator.
   1. more intense
   2. less intense

9. Therefore, areas near ________ should receive more sunlight throughout the year.
   1. the Equator
   2. the Mid-latitudes
   3. the Poles

This can be further reinforced by checking how average air temperatures vary with latitude worldwide. A map of global average air temperatures is shown in Figure \(\PageIndex{5}\). Warmer temperatures are shown in red, while cooler temperatures are shown in blue.

Figure \(\PageIndex{5}\): Global annual average air temperatures. (CC-BY-SA 3.0; Global Warming Art via Wikimedia Commons). Alternative description of the image.

10. While there is some variation caused by other factors (such as elevation, and ocean currents), the warmest temperatures are generally near the ______ while the coldest temperatures are usually near the ________.
    1. poles; equator
    2. equator; poles

11. This _______ the conclusions made in questions 4-6.
    1. confirms
    2. cannot confirm

Earth’s orbit.

However, our Earth is tilted. In fact, it is tilted at an Angle of 23.5°. The result of this is that as the Earth orbits around the sun (Figure \(\PageIndex{6}\)), the latitude at which the sun is directly overhead changes. Figure \(\PageIndex{7}\) represents the conditions in June, when the sun is directly over 23.5°N, while Figure \(\PageIndex{8}\) represents the conditions in December, when the sun is directly over 23.5°S.

Figure \(\PageIndex{6}\): Earth's orbit around the sun and corresponding northern hemisphere seasons. (Public Domain; Tauʻolunga via Wikimedia Commons). Alternative description of the image.

Figure \(\PageIndex{7}\): In June, the northern hemisphere is tilted towards the Sun. (CC BY 4.0; Alicia Mullens). Alternative description of the image.

Figure \(\PageIndex{8}\): In December, the southern hemisphere is tilted towards the Sun. (CC BY 4.0; Alicia Mullens). Alternative description of the image.

12. Based on Figure \(\PageIndex{7}\), in June, the Sun is directly over:
    1. The Equator
    2. 23.5°N
    3. 23.5°S

13. Investigate the North Pole in Figure \(\PageIndex{7}\). Notice that it is completely covered with sunlight. Now imagine the Earth completing one 24-hour rotation around its axis. In June, the North Pole would never:
    1. experience any sunlight
    2. experience any darkness

14. Now let’s investigate Figure \(\PageIndex{8}\), which represents conditions in December. In December, the sun is directly over:
    1. The Equator
    2. 23.5°N
    3. 23.5°S

15. Investigate the North Pole in Figure \(\PageIndex{8}\). Notice that it is pointing away from the Sun. As the Earth completes its 24-hour rotations around its axis, in December, the North Pole would never:
    1. experience any sunlight
    2. experience any darkness