Science · Earth and Space Science
Chapter 1: Earth as a System
What comes in must go out, or the temperature moves.
Earth’s average surface temperature is about 15 °C (59 °F). Yet a simple balance between the sunlight Earth absorbs and the energy it radiates predicts about −18 °C (0 °F), a world of frozen oceans.
Where does the missing 33 °C (59 °F) of warmth come from?
Make your guess to turn the page.
Still to come: 11 pages · Lab · Words to Know · What We Learned · 4 questions · Explain It in Writing · Open Questions
The idea this lesson is working on — Students hear "the greenhouse effect" as a synonym for climate damage, which leaves them unable to explain why Earth is not frozen or to think about degree. The book works the balance to −18 °C and the lab freezes the oceans at zero gas. Ask: does this change the energy arriving or the energy leaving, and where does the balance settle? The idea to reach is that the natural effect is necessary and the enhancement is the question.
What comes in must go out — Earth absorbs solar radiation and emits infrared. If the two are equal the temperature is steady; if outgoing falls short the planet warms until the balance is restored at a higher temperature. CERES measures an imbalance of roughly 1 W/m² (Loeb et al., 2021). The simple balance gives the effective radiating temperature, 255 K; the physical mechanism of the greenhouse effect is that adding absorbers raises the altitude of emission to space, where it is colder.
Albedo decides how much is absorbed — Ice and cloud reflect most incoming sunlight; ocean and forest absorb most of it. Changing surface cover changes the energy budget directly, which is why land use affects climate. Tyndall's measurements were reported in 1859; Eunice Foote's paper was read at the American Association for the Advancement of Science in 1856.