The greenhouse effect is Earth’s built-in heating system. Sunlight reaches the planet’s surface, warms it, and the surface radiates that heat back upward. Greenhouse gases — mainly water vapor, carbon dioxide, methane, and nitrous oxide — absorb some of that outgoing heat and trap it in the atmosphere, like a blanket. Without this natural effect, Earth’s average temperature would be about 0°F (-18°C) instead of the 59°F (15°C) it is now.
The problem is that human activity — burning fossil fuels, deforestation, agriculture — has added extra greenhouse gases to the atmosphere. Carbon dioxide levels have risen by more than 50% since the Industrial Revolution. Methane has increased by about 150%. More greenhouse gas means a thicker blanket, which traps more heat and raises global temperatures.
Water vapor causes about half of the total greenhouse effect naturally. But carbon dioxide, even at a smaller concentration, is the main driver of recent warming because human emissions keep adding it faster than the natural carbon cycle can absorb it.
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