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What Is a Greenhouse Gas?

Greenhouse gases play an important role in climate change

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The burning of fossil fuels is a major contributor to greenhouse gas levels.

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The phrase "greenhouse gas" has become a political hot potato, especially in conversations about global warming and climate change. But not everyone understands what a greenhouse gas is, how the greenhouse effect works, or why greenhouse gases are so critical to life on Earth. Here's a brief introduction to greenhouse gases and their effect on the Earth's climate.

What Is a Greenhouse Gas?

To put it simply, a greenhouse gas, or GHG, is any gas that captures and stores heat. The Earth's atmosphere -- like the atmosphere of some other planets -- is filled with dozens of different gases, some of which function as heat-trapping greenhouse gases.

The most prevalent GHG in the Earth's atmosphere is water vapor, which comes from the evaporation of water in the oceans, lakes and soil. Carbon dioxide (CO2) is another important greenhouse gas; CO2 occurs naturally from animal respiration -- you release CO2 each time you exhale -- and from the burning of plant material (wood, paper) and of fossil fuels (gasoline, oil, natural gas, coal, etc.).

Methane, another greenhouse gas, is also created from biological activity and from the production of fossil fuels. Nitrous oxide, ozone and gases like chlorofluorocarbons (CFCs), hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride are created by agricultural and industrial processes -- these gases also contribute to the total amount of greenhouse gases in our atmosphere.

Not all greenhouse gases are created equal, or pose the same risks: Methane, for example, has about 30 times the heat-trapping ability of CO2. Some researchers therefore believe that releases of methane gas may be a more serious concern than CO2 or other greenhouse gases.

Greenhouse Gases and the Greenhouse Effect

To fully understand how greenhouse gases work, it's important to understand a little bit about how the Earth's atmosphere functions. A simple, everyday example of this occurs in a parked car.

If you park a car outside on a sunny day, sunlight enters through the car's glass windows. That incoming sunlight warms the inside of the car when it shines on the dashboard, the car seats, the steering wheel and other areas. But once the sunlight hits those surfaces, it loses some of its energy, and it can't shine back out of the car. The sunlight's energy -- also called solar radiation -- becomes trapped inside the car, and after an hour or two of sitting in the sun, the inside of the car becomes very warm, even on a cold winter day.

A similar process happens when sunlight shines on the Earth. Some of that solar radiation is absorbed by the atmosphere and by the Earth's surface, so it loses energy. Technically speaking, the powerful incoming shortwave solar radiation loses energy when it shines on the Earth's surface and is converted into longwave radiation, which is weaker and can't escape through the atmosphere. That longwave solar radiation becomes trapped in the atmosphere by greenhouse gases, which get warmer and warmer as the gases absorb more and more solar radiation.

This whole process -- where solar radiation is trapped in the Earth's atmosphere by greenhouse gases -- is often referred to as the "greenhouse effect." A greenhouse, which has glass windows instead of walls, acts like a parked car and absorbs incoming sunlight. That's how tropical plants are able to grow inside a greenhouse, even when the weather outside is cold.

How Do Greenhouse Gases Affect Climate Change?

Ideally, the amount of solar radiation coming into the Earth's atmosphere should be about equal to the amount of solar radiation absorbed, converted into plants, or radiating out into space. That stable situation would result in a stable, steady atmospheric temperature.

However, scientists around the world have noticed two important things in recent decades: The amount of greenhouse gases in the atmosphere has increased dramatically, and the overall temperatures of the atmosphere and the Earth have also increased.

According to the U.S. Energy Information Administration, levels of greenhouse gases have increased 25% since 1850, when fossil fuels like coal and oil started to be widely burned for heating, transportation, manufacturing and other processes. Carbon dioxide is the gas that's largely responsible for this overall increase -- in the United States, roughly 82% of our greenhouse gas emissions are CO2 from burning fossil fuels like gasoline, oil, natural gas and coal.

Scientists worldwide agree that greenhouse gases from human activity -- primarily, the burning of fossil fuels -- are responsible for climate change and global warming. Furthermore, as humans continue to add more greenhouse gases to the atmosphere, the rise in temperatures worldwide is expected to increase dramatically. The combined effects of increased industrial activity (especially in developing countries like China and India), political inertia and ever-increasing global temperatures could have catastrophic impacts to life on Earth.

What You Can Do to Lower GHG Emissions

In the face of an overwhelming challenge like global warming and climate change, it's easy to feel utterly helpless. However, there are a great number of things that people can do on an individual and group level to change things like greenhouse gas emissions. Discover 8 easy things you can do to reduce green house gas levels and help to stave off global climate change.

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