Earth Speak by HowStuffWorks.com

Acid Rain
Acid rain is caused by emissions of sulfur dioxide and nitrogen oxides from power plants, cars and factories. Volcanoes, forest fires and lightning don't help either. Acid rain occurs mostly in the Northern Hemisphere -- the more industrialized, dirtier half of the globe -- but it's still an international issue. Read more interesting facts, such as how acid rain is produced, how it affects natural and man-made objects and how governments aim to reduce it, in this article from HowStuffWorks.

Antarctic Circle
Antarctica is located over the South Pole and is about 1.5 times bigger than the United States. It's the coldest and windiest continent and it's considered a desert due to its lack of rainfall throughout the year. Blizzards are common and often create whiteout conditions, obstructing sight and leaving a person unable to see very far in front of him. Check out HowStuffWorks' maps of Antarctica to see the different areas of the continent, as well as some topographic features.

Arctic Circle
The Arctic Circle comprises the southern region of the Arctic near the North Pole, which marks the area where the sun doesn't set on the summer solstice in June and the sun doesn’t rise on the winter solstice in December. Rich in natural resources, the area has developers searching for oil, natural gas and minerals. See maps of the Arctic -- including the sea, numerous countries and islands it encompasses -- and check out a topographic map to look at some graphic features of the region from HowStuffWorks.com.

Aurora Borealis
The aurora borealis and aurora australis -- or the northern and southern lights -- occur when highly charged electrons from solar wind interact with elements in the atmosphere. Solar winds stream away from the sun at speeds of about one million miles per hour. When they reach Earth 40 hours later, they follow the lines of magnetic force generated by the planet's core and flow through the magnetosphere, a teardrop-shaped area of highly charged electrical and magnetic fields. As the electrons enter Earth's upper atmosphere, they encounter atoms of oxygen and nitrogen at altitudes from 20 to 200 miles above the earth's surface. The color of the aurora depends on which atom is struck and the altitude of the meeting. For example, greens and reds (oxygen) hover in the 150-mile altitude range while blues and purples are in the 60-mile range. Read more about this colorful phenomenon in this article from HowStuffWorks.com.

Biodegradable
"Biodegradable" means that an object can dissolve into raw materials that can safely disappear into the environment. Most materials that come from minerals, plants or animals can be returned to the Earth to degrade. It's when materials come from humans that they're no longer able to disintegrate into the Earth. When humans add chemicals, compounds and other materials to something, Mother Nature doesn't recognize it and therefore can't break it down. Learn more about the Earth, pollution and other green causes throughout HowStuffWorks' science channel.

Biodiversity
Biodiversity is the presence of a large number of different species. If an ecosystem (or planet) is diverse, then the conditions are right to support evolution, reproduction and genetic divergence. In other words, if our planet was a business, then biodiversity means business is good. During warm greenhouse periods, biodiversity suffers. This lack of biodiversity appears to be due to mass extinction -- the loss of large numbers of different species. In this HowStuffWorks article, find out if we're headed toward a mass extinction and what we could possibly do to stop it from occurring.

Biofuels
Biofuels are made from biological ingredients like corn, soy beans or animal fat instead of fossil fuels. Biodiesel is a major biofuel made from plant oils or animal fats as opposed to petroleum. It's also nontoxic and renewable through farming and recycling. Biodiesel can be used safely in its pure form, but it's usually mixed with standard diesel fuel. Learn more about the fats that make up biodiesel, how biofuels came about and some of the pros and cons of using a biofuel in this HowStuffWorks article.

Biosphere
The simplest definition of the biosphere is all life on Earth. That includes humans, animals, plants and all organic matter -- everything that's alive is a part of the biosphere. The biosphere has a hierarchical aspect to it known as the food chain and can be divided by ecosystems. To date, Earth is the only planet in our solar system that contains a biosphere, since no other planet has shown any signs of life forms. To learn more about biospheres, other spheres and our planet in general, head over to HowStuffWorks.com and read How the Earth Works.

Carbon
Carbon is an element of contradicting forms. It's found widely throughout nature in three different ways -- amorphous, graphite and diamond. Graphite is one of the softest known materials on Earth, while a diamond is one of the hardest. Graphite is also black in color, while diamonds are usually colorless. Not only is some form of carbon found throughout Earth, it's also prevalent in the sun, stars, comets and atmospheres of other planets. Find out more about the different elements of Earth at HowStuffWorks' Earth science channel.

Carbon Footprints
While actual footprints measure size, weight and speed, carbon footprints measure how much carbon dioxide (CO2) we produce in our daily lives. A drive to work and a flip of a light switch rely on the combustion of fossil fuels like oil, coal and gas. A carbon footprint is simply a figure -- usually a monthly or annual total of CO2 output measured in tons. By using a carbon calculator, you can turn easy-to-supply information like annual mileage and monthly power usage into a measurable tonnage of carbon. These calculators usually start by asking for your location. Some U.S. states rely on dirtier power sources, such as coal, while others may use renewable sources that produce less CO2. Most calculators use figures like the size of your household and the price of power in your area to determine an estimated electricity usage. The calculator may also take into account if you are a green power subscriber and what your transportation methods are. In this article from HowStuffWorks, learn how carbon calculators come up with your personal total, what it means and how to reduce your CO2 footprint.

Carbon Monoxide
Carbon monoxide is odorless, colorless and tasteless. It's also extremely toxic, and therefore incredibly dangerous, because you can't see, taste or smell it. If you've been exposed to small doses, it may feel like you have the flu, with headaches, dizziness, nausea and fatigue. But it can kill you if you are exposed to enough of what some call the "silent killer." Learn more about how carbon monoxide mixes with your blood to harm you in this article from HowStuffWorks.

Carbon Offsets
Carbon offsets are a form of trade. They let you pay to reduce the global greenhouse gas (GHG) total instead of making radical or impossible reductions of your own. When you buy an offset, you voluntarily fund projects that reduce GHG emissions around the world. Some of these endeavors might help reforestation, increase transportation energy efficiency or update power plant technology. The theory behind carbon offsets can be summed up like this: GHG emissions are a global problem. Carbon offsets operate on the idea that any reduction in any area is worthwhile, whether that means forest planning or converting energy sources to renewable forms. But can carbon neutrality really be bought? HowStuffWorks explores this question.

Carbon Sinks
Carbon is constantly recycled throughout the Earth to be used and then traded. Carbon sources release more carbon than they absorb, while carbon sinks absorb more carbon than they release. Some say that using these carbon sinks would be just as effective as cutting the emissions from fossil fuels, a commitment under the Kyoto Protocol. But others think this is dangerous and should be avoided. How Carbon Trading Works, found at HowStuffWorks.com, goes into more detail about the Kyoto Protocol and carbon emissions.

Chlorofluorocarbons (CFCs)
Chlorofluorocarbons are composed of carbon, fluorine, chlorine and hydrogen and are marketed under the name Freon. They're found in several household products, such as coolants for air conditioners and many cleaning agents. They're nontoxic and nonflammable, which makes them attractive to many manufacturers. While they're safe to use around the house, chlorofluorocarbons have been found to cause severe and permanent damage to the ozone layer. Read about other threats, and solutions to the dangers, at the HowStuffWorks' green science channel.

CITES Treaty
CITES stands for "Convention on International Trade in Endangered Species" of Wild Fauna and Flora. The treaty came into play in 1975, and its purpose is to help save endangered species. The original purpose of the treaty was to regulate international trade of protected species. Over the last 25 years, the organization has worked closely with many groups to set up rules and procedures for sustainable use and conservation worldwide. It currently has 152 member countries, which work under a set of permits and certificates. Visit the science channel at HowStuffWorks.com to learn about animals, endangered species and more animal rights groups.

Clouds
Clouds are formed when billions of water droplets or ice crystals come together. Each year, China sends thousands pellet-filled rockets and artillery shells into the clouds in the sky. The pellets they send into each cloud contain silver iodide, which is thought to cause rain. This process is known as cloud seeding, and China relies heavily on it. But can we really control the weather? It seems to be working; Beijing's water levels are up 13 percent. For more facts about cloud seeding, and to find out why China now wants to prevent rain from falling, read this HowStuffWorks article.

CO2
With every gallon of gas it burns, your car exhausts roughly 20 pounds of carbon dioxide (CO2). This is not to mention the carbon resulting from all of the coal-fired power plants, cleared forests, cow manure from farms and other sources. In total, we humans emit somewhere around 6 billion metric tons of CO2 each year. With this much carbon buildup, we've got to figure out a place to store it. One scientist has suggested burying it on the bottom of the ocean. To find out how this would work, and what it would do to seawater, read this article on HowStuffWorks.com.

Coral Bleaching
Under extreme weather conditions, coral reefs can lose all of their color. This is known as coral bleaching. The most common environmental condition to cause this is higher water temperatures. As global warming becomes more dangerous, the health of the reefs is causing concern among scientists. Read about some other effects of global warming in this HowStuffWorks article.

Cyclone
Early last century, the term "cyclone" was interchangeable with the term "tornado" -- both describing a land-based circular windstorm. That doesn't hold true anymore. Cyclones are now defined as any circular windstorm -- land based or not -- including hurricanes. Hurricanes are technically tropical cyclones that occur in the Atlantic Ocean. Learn how these deadly storms form, how they're named and the damage they can inflict in this article from HowStuffWorks.