Left: Naturally occurring greenhouse gases — carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) — normally trap some of the sun’s heat, keeping the planet from freezing. Right: Human activities, such as the burning of fossil fuels, are increasing greenhouse gas levels, leading to an enhanced greenhouse effect. The result is global warming and unprecedented rates of climate change.
While other planets in Earth's solar system are either scorching hot or bitterly cold, Earth's surface has relatively mild and stable temperatures.
Earth enjoys these temperatures because of its atmosphere — the thin layer of gases that cloak and protect the planet. But humans have changed Earth's atmosphere in dramatic ways over the past two centuries, resulting in global warming.
And to understand global warming, it's first necessary to become familiar with the greenhouse effect.
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