The greenhouse effect

The «greenhouse effect» is the warming that happens when certain gases in Earth’s atmosphere trap heat. These gases let in light but keep heat from escaping, like the glass walls of a greenhouse, hence the name.Sunlight shines onto the Earth’s surface, where the energy is absorbed and then radiate back into the atmosphere as heat. In the atmosphere, greenhouse gas molecules trap some of the heat, and the rest escapes into space. The more greenhouse gases concentrate in the atmosphere, the more heat gets locked up in the molecules.

Scientists have known about the greenhouse effect since 1824, when Joseph Fourier calculated that the Earth would be much colder if it had no atmosphere. This natural greenhouse effect is what keeps the Earth’s climate livable. Without it, the Earth’s surface would be an average of about 60 degrees Fahrenheit (33 degrees Celsius) cooler.

Levels of greenhouse gases have gone up and down over the Earth’s history, but they had been fairly constant for the past few thousand years. Global average temperatures had also stayed fairly constant over that time—until the past 150 years. Through the burning of fossil fuels and other activities that have emitted large amounts of greenhouse gases, particularly over the past few decades, humans are now enhancing the greenhouse effect and warming Earth significantly, and in ways that promise many effects, scientists warn.