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Briefing: The Greenhouse Effect

The greenhouse effect makes life on Earth possible

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The greenhouse effect is rapidly heating up Earth's atmosphere.

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As natural phenomena go, the greenhouse effect has to be one of the most bipolar: It makes life on Earth possible, but when it overacts and contributes to climate change and global warming, the greenhouse effect wreaks worldwide havoc and makes parts of the Earth almost uninhabitable.

How the Greenhouse Effect Works

To understand the greenhouse effect, it's important to know a little of the basic physics that underlay this important concept. One useful everyday example is a car parked outdoors on a cool, sunny day. When the windows are rolled up, the inside of the car gets warmer than the outside air. Here's how:

We'll start with the sun, which sends out visible light as well as other kinds of radiation that humans can't see, including ultraviolet (UV) radiation and infrared (IR) radiation. UV radiation is relatively high in energy -- it's what causes sunburns and oxidizes paint -- and it has a shorter wavelength; IR radiation is somewhat weaker and has a longer wavelength.

When sunlight hits the Earth, visible light, UV and IR radiation fall through the atmosphere. This radiant energy strikes the surfaces of oceans, land, plants, roads and buildings, heating them up. But not all of this radiation is absorbed -- after striking the Earth, some of the energy is reflected back out from the surface, though in a weaker form, usually as IR radiation that, once again, has a shorter wavelength.

When this weaker IR radiation is reflected back out from the Earth's surface, it must travel through the atmosphere, where it meets gases like oxygen, nitrogen, argon and the other gases that make up the atmosphere.

Some of these gases are known as greenhouse gases; examples include water vapor, carbon dioxide (CO2) and methane. These gases, because of their molecular structure, are very good at absorbing some of the outgoing infrared radiation. Greenhouse gases absorb heat energy from IR radiation and hold it in the atmosphere.

This is basically what happens inside a car parked outside on a cool, sunny day: Sunlight comes through the car's windows, and that solar radiation is absorbed by the upholstery, the dashboard, the steering wheel, etc. Some of that radiation bounces back out, but is too weak to pass through the windows again, so it's trapped inside the car, which then heats up after just a few hours in the sun, even on a cold winter day.

This is also how a glass greenhouse works, keeping tropical plants blooming even in a wintry climate -- thus the terms "greenhouse gas" and "greenhouse effect." Due to the greenhouse effect, the global average temperature is roughly 57 degrees F. Without the greenhouse effect and the atmosphere's ability to capture IR radiation, the global average temperature would be much colder, about 0 degrees F.

Why the Greenhouse Effect Is Important

Since the greenhouse effect warms the Earth's surface and atmosphere, we have the relatively mild, life-sustaining climate in which all life has evolved. But ever since the Industrial Revolution got into full swing in the 1800s, we have been burning enormous amounts of carbon-based fuels like coal, oil, gasoline and natural gas. And when these carbon-based fuels are burned, they release enormous amount of CO2, one of the greenhouse gases that is most adept at absorbing radiation.

Of course, the combustion of carbon-based fuels has been going on long before the rise of human civilization: forest fires, volcanoes and plant and animal metabolism release CO2 and other greenhouse gases into the atmosphere. The amount of CO2 in the atmosphere has increased from about 289 parts per million before the Industrial Revolution to over 360 parts per million -- and rising.

Higher CO2 levels in the atmosphere bring a stronger greenhouse effect and therefore warmer temperatures worldwide. According to the National Oceanic and Atmospheric Administration (NOAA), global surface temperatures have increased about 33 degrees Fahrenheit since the late 1800s.

Additionally -- and alarmingly -- seven of the eight warmest years on record have occurred since 2001, and the 10 warmest years have all occurred since 1995. These facts leave climate change skeptics with virtually nothing to substantiate their increasingly meaningless position.

What You Can Do About the Greenhouse Effect

Given the harsh realities of climate change as caused by the greenhouse effect, many people are rightfully concerned about what can be done to reverse the trend toward global warming. Less driving and more use of public transportation, use of insulation with a higher R-value to decrease the fuel burned to heat and cool our homes, more efficient appliances and use of energy-efficient light bulbs will reduce our energy needs in the short term.

In the long term, converting to green or renewable energy sources like wind, geothermal and solar which don't emit CO2 into the atmosphere is imperative. Sustainable agriculture that doesn't rely on heavy use of fertilizer, meat-based proteins or petroleum-based additives will also make a huge difference. And stopping deforestation in the forests around the world will keep more carbon on Earth rather than sending it back into the atmosphere.

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