Environmental Science / Unit 7: Air Pollution and Climate
7.5 The Greenhouse Effect
Notes
The greenhouse effect is a natural process that keeps Earth warm enough for life.
- Sunlight warms Earth's surface. The surface emits infrared (heat) radiation. Greenhouse gases absorb some of this heat and re-radiate it, warming the lower atmosphere.
- Without the natural greenhouse effect, Earth's average temperature would be about $-18^\circ\text{C}$ instead of about $15^\circ\text{C}$.
- Main greenhouse gases: water vapor, carbon dioxide ($CO_2$), methane ($CH_4$), nitrous oxide ($N_2O$), and fluorinated gases.
- Human sources: $CO_2$ from burning fossil fuels and deforestation; $CH_4$ from livestock, rice paddies, landfills, and natural gas leaks; $N_2O$ from fertilizers.
- Global warming potential (GWP) compares gases: methane traps much more heat per molecule than $CO_2$ over 100 years (about 28 times) but stays in the air for a shorter time (about 12 years).
- The enhanced greenhouse effect is the extra warming caused by human additions of these gases.
- Example: $CO_2$ rose from about 280 parts per million (ppm) before the Industrial Revolution to over 420 ppm today.
Practice
What is the natural greenhouse effect?
Without it Earth would be far colder.
Which activity releases the most methane?
Cattle digestion, rice paddies, and landfills are major sources of methane.
Atmospheric $CO_2$ rose from about 280 ppm to about 420 ppm. By how much did it increase, and what is the percent increase?
$420 - 280 = 140$, and $\displaystyle \frac{140}{280} = 0.50$ or 50%.
Ready for more? Take the Unit 7 test.