Final answer:
Without greenhouse gases, the Earth's average temperature would be -18°C, which is below the freezing point of water (0°C). Greenhouse gases are responsible for the insulation that makes life on Earth possible by maintaining average temperatures around 15°C. Absence of these gases would result in a global ice age, rendering the planet unsuitable for most life forms.
Step-by-step explanation:
If there were no greenhouse gases in our atmosphere, such as water vapor and carbon dioxide, the average temperature of the Earth would be significantly colder. The naturally occurring greenhouse effect is vital in keeping our planet warm enough to sustain life. Without it, Earth's average temperature would plummet to about -18°C (0°F), which is below the freezing point of water. Greenhouse gases work by trapping heat from the sun, specifically the long-wave infrared radiation emitted by the warmed Earth, creating an insulating layer that prevents this heat from escaping back into space.
This warming effect is what allows the Earth to have a surface temperature that averages around 15°C (59°F) instead of the -18°C that would exist without the greenhouse effect. Therefore, without these gases, the Earth would be in a perpetual global ice age, and life as we know it would not be possible. The current concerns with the greenhouse effect relate to the enhanced or anthropogenic effects that are due to human activities, such as the burning of fossil fuels and deforestation, which increase the concentration of these gases in the atmosphere and drive global warming.