Step 1: The sun’s radiation travels toward earth.
Step 2: When it travels through the atmosphere, clouds and the atmosphere itself reflect about one-third of the radiation back toward the sun. They also absorb about twenty percent of it.
Step 3: The rest of the radiation–about fifty percent–reaches earth, where it is absorbed by oceans and land. This keeps the earth warm and sustains plant, animal, and human life.
Step 4: The earth also releases heat back toward space.
Step 5: Some of this heat passes directly through the atmosphere.
Step 6: But most of it is captured and retained by greenhouse gases before it can escape. This is the mechanism that keeps the earth warm.
Normally, the greenhouse effect keeps the earth just warm enough to sustain life. Scientists say that without the greenhouse effect, the average temperature of the earth would drop from 14˚C (57˚F) to as low as −18˚C (−0.4˚F). But these days, through human activities like deforestation and fossil fuel use, more greenhouse gases like carbon dioxide are being released into the atmosphere. This traps more heat and causes global warming.