2. The greenhouse effect retains some of the sun’s warmth and makes Earth habitable for plants and animals.
Without this effect, described in Additional Fact #1, Earth's surface would be frozen. More than 90% of Earth's greenhouse effect is due to water in its liquid and gaseous forms. The contribution of CO2 is significant in determining Earth's climate only in low saturations because its ability to trap more heat radiated from Earth's surface into the atmosphere declines very rapidly, logarithmically, as more and more CO2 is added to the atmosphere.