Sun Angle by Latitude – Climate Zones and the Greenhouse Effect
GeographyWeather & ClimateAges 11–12
Use it with your class: students open it from a link or a QR code, with no account needed.
Next in Weather & Climate
A beam of sunlight of equal width strikes the Earth: at the equator the rays hit nearly straight down, so energy is concentrated, while toward the poles the angle shrinks and the same amount of heat spreads over a wider area, making it colder. Drag the marker along the edge of the globe (or the latitude slider) to see how the angle of incidence, the spread of the beam, the estimated average temperature and the climate zone (tropical, temperate, polar, bounded by 23°27′ and 66°33′) all change. Drag the CO₂ slider to see how greenhouse gases trap heat radiation and warm the Earth.
Lesson: Air temperature; Earth's climate zones; climate change and responses
What it shows
Why is it hotter at the equator than at the poles? Not because the poles are farther from the Sun, but because of the angle at which sunlight arrives. A beam of fixed width that strikes the ground at an angle h spreads over an area 1/sin h times larger. The latitude where the noon Sun is directly overhead shifts between the Tropic of Cancer and the Tropic of Capricorn, which fixes the boundaries of the five climate zones. A simple greenhouse model adds about 3 °C of warming for each doubling of CO₂.
How to use
Start on Equinox at the equator and drag the marker along the globe's edge, or the Latitude slider, toward a pole while reading the angle of incidence and the beam spread. Switch to Summer solstice and Winter solstice to see where the Sun is overhead. Turn on Show climate zones to read the tropics and polar circles, then raise the CO₂ slider with Show greenhouse effect diagram on. The 3D view shows parallel beams landing at several latitudes at once.
Parameters you can change
- Latitude (negative = Southern Hemisphere) -90–90 °
- Atmospheric CO₂ concentration 150–1200 ppm
- Time of year Spring / autumn equinox, around 20 March / 22–23 September (Sun directly overhead at equator), Summer solstice, around 21 June (directly overhead at Tropic of Cancer), Winter solstice, around 21 December (directly overhead at Tropic of Capricorn)
- Show greenhouse effect diagram
- Show climate zones
Questions to explore
- At the summer solstice, at which latitude is the noon Sun directly overhead, and what is the angle of incidence there?
- On the equinox, how many times wider does the same beam spread at 60° latitude than at the equator?
- How much does the estimated temperature change when CO₂ is doubled from 280 to 560 ppm?
