Without its atmosphere—the envelope of gases that surrounds a planet or moon—the Earth would be unrecognizable. With no gases for light or sound to travel through, the skies would be black and silent. With no air in which to float or fly, pollen, birds, and airplanes would fall to the ground. Of course, there would be no plants, animals, or airplanes, since there would be no gaseous molecules to support life or to protect organisms from the Sun's harmful, high-energy radiation. The planet would be uninhabitable, except perhaps for the simplest life forms. As on the Moon, temperatures would be scorching in the day and frigid at night, and the temperature difference between the equator and the poles would be extreme. There would be no weather—clouds could not form and rain would not fall—and, by extension, there would be no climate. It would be a very different world: a world more like Mars than the Earth.

Fortunately, the Earth does have an atmosphere, even though it is very thin when compared to the size of the planet. Its gases provide some of the raw ingredients necessary for the manufacture of food by plants and for the use of food energy by living things. Ozone gas clustered in a layer of the upper atmosphere protects the planet's life by filtering out the incoming radiation of the Sun's most harmful rays. Greenhouse gases store heat, resulting in global temperatures that are much more moderate than they otherwise would be.

The atmosphere is the location of all weather, whether it is a mild summer breeze or a devastating hurricane. The weather may bring much-needed rain or an unremitting drought. Winds serve the planet by delivering heat from warmer regions to cooler ones, resulting in

a more evenly heated globe. Rains convey moisture from wet regions— especially from the oceans—to drier areas, allowing them to be inhabited by plants and animals. A region's climate is the long-term average pattern of its weather, which is shaped by its latitude, its position in atmospheric circulation patterns, and its proximity to oceans and mountain ranges, among other features.

The atmosphere is useful to humans for more than just these natural processes. People exploit the atmosphere's vastness by using it as a repository for the gaseous waste products of industrial society. And now the quantity of air pollution is overtaking us. Cities, rural areas, and even national parks are plagued by polluted air. Pollutants created by the burning of fuels or forests or by the manufacture of chemicals rise into the air above an area, resulting in reduced visibility, an altered environment, and compromised human health. Some pollutants combine with water in the atmosphere to create acids that fall as rain. This acid rain degrades forests, freshwater environments, and cultural objects. Even heat can be a pollutant. Some urban areas have experienced temperature increases in recent decades due to waste heat from modern machinery and the way that concrete and other manmade surfaces intensify the effects of solar radiation. Programs to reduce pollution have been very successful with some pollutants in some areas, although as populations and machinery increase, there is always more that needs to be done.

Earth's atmosphere is an extremely thin layer compared to the size of the planet. (NASA)

Air pollutants do not just harm the local or regional environment; they also can cause damage on a global scale. Certain man-made chemicals have damaged the planet's protective ozone layer, allowing more harmful solar radiation to strike the Earth's surface. Although the use of these chemicals is being phased out, their destructive effects will linger for many more decades. Rising concentrations of greenhouse gases, the result of human activities like fossil fuel burning, have boosted global temperatures. This has already brought about a rise in sea level, more extreme weather, and melting glaciers and ice caps. Many more alterations to the environment are inevitable as temperatures continue to climb. Efforts to reduce greenhouse gas emissions have had only limited success thus far, but the world is becoming increasingly aware of the need to find solutions.

Part One of Atmosphere describes the function of the atmosphere and discusses interesting phenomena such as the cause of rainbows. Part Two looks at the weather, both normal and extreme, and shows why even the most extreme weather is normal for some locations. Air pollutants and their effect on the environment and human health are covered in Part Three. Pollutants that cause global damage, either by destroying the ozone layer or by causing global warming, are discussed in Part Four.



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Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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