Click image to open full size
Environmental Science
Climate Change
How Greenhouse Gases Warm Our Planet
Related Tools
Related Worksheets
Earth stays warm because its atmosphere lets most incoming sunlight reach the surface while slowing the escape of heat back to space. This natural greenhouse effect makes the planet habitable, but human activities are strengthening it. Burning fossil fuels, cutting forests, and some farming practices add extra greenhouse gases to the air. As these gases build up, more infrared radiation is absorbed and redirected, raising Earth’s average temperature.
Key Facts
- Incoming solar energy is mostly shortwave radiation, while Earth emits outgoing heat as longwave infrared radiation.
- The greenhouse effect occurs when gases absorb infrared radiation and re-emit it in all directions.
- Main greenhouse gases include H2O, CO2, CH4, N2O, and O3.
- Energy balance condition: incoming solar energy = outgoing infrared energy at equilibrium.
- Radiative forcing measures a change in Earth’s energy balance in W/m^2.
- Carbon dioxide concentration is often reported in parts per million: ppm = (CO2 molecules / air molecules) x 1,000,000.
Vocabulary
- Greenhouse gas
- A gas in the atmosphere that absorbs and re-emits infrared radiation, helping trap heat near Earth’s surface.
- Infrared radiation
- Longwave electromagnetic radiation emitted by warm objects, including Earth’s surface and lower atmosphere.
- Radiative forcing
- A measure of how much a factor changes the balance between incoming solar energy and outgoing heat energy.
- Albedo
- The fraction of incoming sunlight reflected by a surface, such as ice, clouds, land, or ocean.
- Carbon cycle
- The movement of carbon among the atmosphere, oceans, living organisms, rocks, and soils.
Common Mistakes to Avoid
- Thinking the greenhouse effect is entirely harmful. The natural greenhouse effect is necessary for life, while the problem is the enhanced greenhouse effect caused by extra greenhouse gases.
- Confusing ozone layer depletion with climate change. Ozone depletion is mainly about increased ultraviolet radiation reaching Earth, while climate change is mainly driven by changes in heat-trapping gases.
- Assuming greenhouse gases block incoming sunlight the same way they trap heat. Most visible sunlight passes through the atmosphere, but infrared radiation from Earth is strongly absorbed by greenhouse gases.
- Using one cold day as evidence against global warming. Climate describes long-term patterns over decades, while weather describes short-term conditions in a specific place.
Practice Questions
- 1 A sample of air contains 420 CO2 molecules per 1,000,000 air molecules. What is the CO2 concentration in ppm?
- 2 If Earth absorbs 240 W/m^2 of solar energy and emits 236 W/m^2 of infrared energy to space, what is the net energy gain in W/m^2?
- 3 Explain why melting sea ice can increase warming even though ice itself is not a greenhouse gas.