The greenhouse effect is the way heat is trapped near the Earth’s surface by “greenhouse gases”. These heat-trapping gases can be thought of as a blanket that wraps around the Earth, keeping the planet warmer than it would be without it. Greenhouse gases include carbon dioxide, methane, nitrous oxides, and water vapor. (Water vapor, which responds physically or chemically to changes in temperature, is called a “feedback.”) Scientists have determined that the warming effect of carbon dioxide helps stabilize the Earth’s atmosphere. By removing carbon dioxide, the Earth’s greenhouse effect would collapse. Without carbon dioxide, Earth’s surface would be about 33°C (59°F) cooler.

Greenhouse gases occur naturally and are part of the composition of our atmosphere. For that reason, Earth is sometimes called the “Goldilocks” planet: its conditions are neither too hot nor too cold, but just right to allow life (including us) to flourish. Part of what makes Earth so docile is its natural greenhouse effect, which keeps the planet at a friendly average of 15 °C (59 °F). But in the last century or so, humans have been interfering with the planet’s energy balance, mainly through the burning of fossil fuels that add carbon dioxide to the air. The level of carbon dioxide in the Earth’s atmosphere has been rising steadily for decades and traps extra heat near the Earth’s surface, causing temperatures to rise.