Example 1
A simplified Earth system absorbs 240 energy-units and emits 237 per interval. Find its net energy gain.
Net gain = absorbed − emitted =240−237=+3 energy-units per interval. Stored energy increases.
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Year 10
Earth’s energy balance and the greenhouse effect
Account for incoming, reflected and outgoing energy and identify greenhouse-gas effects.
Method and worked examples
Sunlight supplies energy to Earth. Some is reflected by clouds, air and surfaces; the remainder is absorbed by the surface and atmosphere. Earth emits infrared radiation towards space. When absorbed energy equals outgoing energy over a suitable interval, the system has no net energy gain. More absorbed than emitted energy raises stored energy until the balance changes. This is a whole-Earth energy budget.
Greenhouse gases absorb and emit infrared radiation, altering transfers between the surface, atmosphere and space. The natural greenhouse effect keeps the surface warmer than it would otherwise be. Increasing long-lived greenhouse gases changes the outgoing-energy balance and drives warming until a new balance is approached. This is not the same mechanism as the ozone hole, and gases do not form a solid lid preventing all energy escape.
Example 1
Example 2
Which radiation is most directly involved when greenhouse gases absorb energy emitted by Earth?
Outgoing infrared radiation. This differs from claiming greenhouse gases block all incoming sunlight.
Watch out: Greenhouse warming is primarily about infrared absorption and emission by greenhouse gases. Ozone depletion is a distinct issue.