Greenhouse Gas Science
Describe the electromagnetic spectrum and distinguish between short-wave solar radiation and long-wave infrared radiation emitted by Earth; explain how greenhouse gas molecules (CO2, CH4, N2O, H2O) absorb and re-emit infrared through molecular vibration while O2 and N2 do not; distinguish the natural greenhouse effect (which makes Earth habitable) from the enhanced greenhouse effect driven by human emissions; evaluate the relative potency of different greenhouse gases
The lesson
Sunlight reaches Earth as short-wave light, the kind your eyes can see. Earth's surface soaks up that light, warms up, and sends energy back out as a different kind of light: long-wave infrared. You can't see infrared, but you can feel it as heat.
CO2, methane (CH4), nitrous oxide (N2O), and water vapor (H2O) are each built from different kinds of atoms bonded together, so their bonds can stretch and bend. When outgoing infrared hits one of these molecules, the bending motion absorbs the energy. The molecule then re-emits that energy in a random direction, sometimes back toward the ground. Oxygen (O2) and nitrogen (N2) are each just two atoms of the same element joined by a simple bond. That bond doesn't flex the same way, so infrared light passes right through them.
Without any greenhouse gases, Earth's surface would average around 0°F (-18°C), a deep freeze. Because CO2, methane, water vapor, and other greenhouse gases trap some outgoing infrared, Earth actually averages about 59°F (15°C). That natural greenhouse effect is why oceans stay liquid and plants can grow. Since the 1800s, people have added extra CO2 and methane by burning coal, oil, and gas. Those extra molecules trap even more infrared on top of the natural effect, warming the planet beyond its usual balance. That extra warming is called the enhanced greenhouse effect.
When you compare gases, think about both amount and potency. CO2 is far more common in the air, but methane and nitrous oxide each trap more heat per molecule.
Greenhouse gases flex and catch outgoing infrared heat because of how their atoms bond, while O2 and N2 can't, and today's extra emissions add on top of the natural effect that already keeps Earth warm enough to live on.
Watch it
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.