Questions: The Greenhouse Effect Basics

Question 1

Without the natural greenhouse effect, what would Earth's average surface temperature be?

• A. About the same as it is now — 15 degrees Celsius
• B. About -18 degrees Celsius — too cold for liquid water
• C. About 100 degrees Celsius — too hot for life
• D. About 0 degrees Celsius — just at the freezing point

Answer: (B)

Without greenhouse gases trapping heat, Earth's average surface temperature would be about -18 degrees Celsius (0 degrees Fahrenheit). The natural greenhouse effect raises it to about +15 degrees Celsius (59 degrees Fahrenheit) — a 33-degree difference that makes liquid water, and therefore life, possible. The greenhouse effect is not the problem; the problem is the enhanced greenhouse effect from human emissions.

Question 2

Explain how adding more CO2 to the atmosphere leads to warming.

Model answer: More CO2 molecules in the atmosphere absorb more of the infrared radiation (heat) emitted by Earth's surface. This absorbed energy is re-radiated in all directions, including back toward the surface. More CO2 means more heat is returned to the surface instead of escaping to space, raising the surface temperature. It is like adding an extra blanket — the Sun provides the same amount of heat, but less of it escapes.

This is a direct, well-understood physical mechanism. CO2 molecules vibrate at frequencies that match infrared radiation, allowing them to absorb and re-emit it. Doubling CO2 concentration does not double the warming (the relationship is logarithmic), but it does produce significant additional warming, amplified by feedback mechanisms like increased water vapor.

Question 3

The greenhouse effect works the same way as a glass greenhouse — by trapping warm air inside.

• T. True
• F. False

Answer: False

Despite the name, the mechanisms are different. A glass greenhouse works by preventing convection — warm air cannot rise and escape through the glass roof. The atmospheric greenhouse effect works through radiation: greenhouse gas molecules absorb outgoing infrared radiation and re-emit it in all directions, returning some heat to the surface. The name 'greenhouse effect' is a metaphor, not a precise description of the physics.