What are greenhouse gases?

Greenhouse gases are molecules in the atmosphere that absorb long-wavelength infrared energy radiated by the Earth. These  molecules move more rapidly when they absorb this energy and warm up the atmosphere.  These gases—like carbon dioxide (CO₂)—are referred to as greenhouse gases because, like the glass of a greenhouse, they let visible light from the Sun pass through the atmosphere but they absorb long-wavelength infrared energy from the Earth and keep the atmosphere warm.

Featured
Earth has a balanced energy budget. Incoming energy from the Sun is balanced by outgoing energy emitted by the Earth. Sunlight consists of visible, infrared, and ultraviolet light.  The Sun radiates visible light most strongly, and the sunligh

Earth has a balanced energy budget. Incoming energy from the Sun is balanced by outgoing energy emitted by the Earth.

Sunlight consists of visible, infrared, and ultraviolet light.  The Sun radiates visible light most strongly, and the sunlight that reaches the Earth’s surface is mostly visible light.

The Earth’s surface absorbs the visible sunlight and warms. Then it re-radiates the absorbed energy at long infrared wavelengths. Even though the Earth is radiating energy, we don’t see it glow because long-wavelength infrared energy is invisible to

The Earth’s surface absorbs the visible sunlight and warms. Then it re-radiates the absorbed energy at long infrared wavelengths. Even though the Earth is radiating energy, we don’t see it glow because long-wavelength infrared energy is invisible to people.

Most gases in the atmosphere are transparent to infrared energy, but some gases, like carbon dioxide and methane, absorb infrared.

When carbon dioxide absorbs infrared energy, the molecules vibrate and collide with other gas molecules. This raises the temperature of the atmosphere.  The absorbed energy is re-radiated in all directions: some back to Earth, some out to space

When carbon dioxide absorbs infrared energy, the molecules vibrate and collide with other gas molecules. This raises the temperature of the atmosphere.  The absorbed energy is re-radiated in all directions: some back to Earth, some out to space, some re-absorbed by other molecules.

Gases that absorb infrared energy are called greenhouse gases. The more greenhouse gases in the atmosphere, the warmer the atmosphere gets before the outgoing infrared energy finally leaves the Earth system.

Gases that absorb infrared energy are called greenhouse gases. The more greenhouse gases in the atmosphere, the warmer the atmosphere gets before the outgoing infrared energy finally leaves the Earth system.

Where do greenhouse gases come from?

Greenhouse gases (GHGs) can come from natural sources, such as CO₂ from volcanoes and decomposing plants, or methane from swamplands. But these sources are not responsible for the recent rapid increase in concentrations of GHGs in our atmosphere. Extracting and burning fossil fuels releases CO₂, methane, and nitrous oxide, another GHG. GHGs also come from materials in our refrigerators and air conditioners, solvents, and fire suppressants. Some come from agriculture, cement production, and from waste decomposing in landfills. The ways that we use land, such as cutting down forests to build farms, can lead to release of GHGs.

infographic.png

What do you think the world would look like if we could see greenhouse gases?
What parts of your community are the biggest emitters?

Learn more about the greenhouse effect on the Paleontological Research Institution’s Digital Encyclopedia and in these videos:

Dig deeper into climate change and energy on the Learn More page of this exhibit.