• greenhouse effect
    The greenhouse effect is a vital natural phenomenon, intensified by human activity.

    Manmade Gas
    Chlorofluorocarbons (CFCs) are the only greenhouse gases not created by nature. Other greenhouse gases, such as carbon dioxide, are emitted by human activity, but the molecules also occur naturally in the Earth's atmosphere. CFCs, used mostly as refrigerants, are chemicals that were developed in the late 19th century and came into wide use in the mid-20th century. Many countries, including the United States, are phasing out use of CFCs because of the danger they pose to the environment.

    The greenhouse effect happens when certain gases—known as greenhouse gases—collect in Earth’s atmosphere. These gases include carbon dioxide (CO2), methane, nitrous oxide (N2O), fluorinated gases, and ozone.

    Greenhouse gases let the sun’s light shine onto the Earth’s surface, but they trap the heat that reflects back up into the atmosphere. In this way, they act like the glass walls of a greenhouse. This greenhouse effect keeps the Earth warm enough to sustain life. Scientists say that without the greenhouse effect, the average temperature of the Earth would drop from 14˚C (57˚F) to as low as –18˚C (–0.4˚F).

    Some greenhouse gases come from natural sources. Evaporation adds water vapor to the atmosphere. Animals and plants release carbon dioxide when they respire, or breathe. Methane is released naturally from some low-oxygen environments, such as swamps. Nitrous oxide is produced by certain processes in soil and water. Volcanoes—both on land and under the ocean—release greenhouse gases, so periods of high volcanic activity tend to be warmer. 

    Since the Industrial Revolution of the late 1700s and early 1800s, people have been releasing large quantities of greenhouse gases into the atmosphere. That amount has skyrocketed in the past century. Greenhouse gas emissions increased 70 percent between 1970 and 2004. Emissions of CO2, the most important greenhouse gas, rose by about 80 percent during that time. The amount of CO2 in the atmosphere today far exceeds the natural range seen over the last 650,000 years.

    Most of the CO2 that people put into the atmosphere comes from burning fossil fuels. Cars, trucks, trains, and planes all burn fossil fuels. Many electric power plants do, as well. Another way humans release CO2 into the atmosphere is by cutting down forests, because trees contain large amounts of carbon.

    People add methane to the atmosphere through livestock farming, landfills, and fossil fuel production such as coal mining and natural gas processing. Nitrous oxide comes from agriculture and fossil fuel burning. Fluorinated gases include chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and hydrofluorocarbons (HFCs). These gases are used in aerosol cans and refrigeration.

    All of these human activities add greenhouse gases to the atmosphere. As the level of these gases rises, so does the temperature of the Earth. The rise in Earth’s average temperature contributed to by human activity is known as global warming.


    The Greenhouse Effect and Climate Change

    Even slight increases in average global temperatures can have huge effects. Perhaps the biggest, most obvious effect is that glaciers and ice caps melt faster than usual. The meltwater drains into the oceans, causing sea levels to rise.

    Glaciers and ice caps cover about 10 percent of the world’s landmasses. They hold about 75 percent of the world’s freshwater. If all of this ice melted, sea levels would rise by about 70 meters (230 feet). The Intergovernmental Panel on Climate Change states that the global sea level rose about 1.8 millimeters per year from 1961 to 1993, and 3.1 millimeters per year since 1993.

    Rising sea levels could flood coastal cities, displacing millions of people in low-lying areas such as Bangladesh, the U.S. state of Florida, and the Netherlands. Millions more people in countries like Bolivia, Peru, and India depend on glacial meltwater for drinking, irrigation, and hydroelectric power. Rapid loss of these glaciers would devastate those countries.

    Greenhouse gas emissions affect more than just temperature. Another effect involves changes in precipitation, such as rain and snow. Over the course of the 20th century, precipitation increased in eastern parts of North and South America, northern Europe, and northern and central Asia. However, it has decreased in parts of Africa, the Mediterranean, and southern Asia.

    As climates change, so do the habitats for living things. Animals that are adapted to a certain climate may become threatened. Many human societies depend on specific crops for food, clothing, and trade. If the climate of an area changes, the people who live there may no longer be able to grow the crops they depend on for survival. Some scientists also worry that tropical diseases will expand their ranges into more temperate regions if the temperatures of those areas increase.

    Most climate scientists agree that we must reduce the amount of greenhouse gases released into the atmosphere. There are lots of ways to do this, including:

    • Fly less. Airplanes produce huge amounts of greenhouse gas emissions.
    • Plant a tree. Trees absorb carbon dioxide, keeping it out of the atmosphere.
    • Eat less meat. Cows are one of the biggest methane producers.
    • Support alternative energy sources that don’t burn fossil fuels.
  • Term Part of Speech Definition Encyclopedic Entry
    aerosol can Noun

    container of liquid material under high pressure. When released through a small opening, the liquid becomes a spray or foam.

    agriculture Noun

    the art and science of cultivating the land for growing crops (farming) or raising livestock (ranching).

    Encyclopedic Entry: agriculture
    atmosphere Noun

    layers of gases surrounding a planet or other celestial body.

    Encyclopedic Entry: atmosphere
    carbon Noun

    chemical element with the symbol C, which forms the basis of all known life.

    carbon dioxide Noun

    greenhouse gas produced by animals during respiration and used by plants during photosynthesis. Carbon dioxide is also the byproduct of burning fossil fuels.

    chlorofluorocarbon (CFC) Noun

    chemical compound mostly used in refrigerants and flame-retardants. Some CFCs have destructive effects on the ozone layer.

    climate Noun

    all weather conditions for a given location over a period of time.

    Encyclopedic Entry: climate
    coal Noun

    dark, solid fossil fuel mined from the earth.

    coast Noun

    edge of land along the sea or other large body of water.

    Encyclopedic Entry: coast
    crop Noun

    agricultural produce.

    Encyclopedic Entry: crop
    electricity Noun

    set of physical phenomena associated with the presence and flow of electric charge.

    environment Noun

    conditions that surround and influence an organism or community.

    evaporation Noun

    process by which liquid water becomes water vapor.

    Encyclopedic Entry: evaporation
    flood Noun

    overflow of a body of water onto land.

    Encyclopedic Entry: flood
    fluorinate Verb

    to add or combine with the element fluorine (F).

    forest Noun

    ecosystem filled with trees and underbrush.

    fossil fuel Noun

    coal, oil, or natural gas. Fossil fuels formed from the remains of ancient plants and animals.

    freshwater Noun

    water that is not salty.

    gas Noun

    state of matter with no fixed shape that will fill any container uniformly. Gas molecules are in constant, random motion.

    glacier Noun

    mass of ice that moves slowly over land.

    Encyclopedic Entry: glacier
    global warming Noun

    increase in the average temperature of the Earth's air and oceans.

    Encyclopedic Entry: global warming
    greenhouse Noun

    building, often made of glass or other clear material, used to help plants grow.

    greenhouse effect Noun

    phenomenon where gases allow sunlight to enter Earth's atmosphere but make it difficult for heat to escape.

    Encyclopedic Entry: greenhouse effect
    greenhouse gas Noun

    gas in the atmosphere, such as carbon dioxide, methane, water vapor, and ozone, that absorbs solar heat reflected by the surface of the Earth, warming the atmosphere.

    habitat Noun

    environment where an organism lives throughout the year or for shorter periods of time.

    Encyclopedic Entry: habitat
    hydrochlorofluorocarbon Noun

    greenhouse gas often used as an industrial cooling material.

    hydroelectric power Noun

    usable energy generated by moving water converted to electricity.

    hydrofluorocarbon Noun

    greenhouse gas often used as an industrial cooling material.

    ice cap Noun

    area of fewer than 50,000 square kilometers (19,000 square miles) covered by ice.

    Encyclopedic Entry: ice cap
    Industrial Revolution Noun

    change in economic and social activities, beginning in the 18th century, brought by the replacement of hand tools with machinery and mass production.

    irrigation Noun

    watering land, usually for agriculture, by artificial means.

    Encyclopedic Entry: irrigation
    landfill Noun

    site where garbage is layered with dirt and other absorbing material to prevent contamination of the surrounding land or water.

    livestock noun, plural noun

    animals raised for sale and profit.

    meltwater Noun

    freshwater that comes from melting snow or ice.

    methane Noun

    chemical compound that is the basic ingredient of natural gas.

    microbial Adjective

    having to do with very small organisms.

    mining Noun

    process of extracting ore from the Earth.

    molecule Noun

    smallest physical unit of a substance, consisting of two or more atoms linked together.

    natural gas Noun

    type of fossil fuel made up mostly of the gas methane.

    Encyclopedic Entry: natural gas
    nitrous oxide Noun

    greenhouse gas used in medicine and the manufacture of rockets. Also known as laughing gas or happy gas.

    ocean Noun

    large body of salt water that covers most of the Earth.

    Encyclopedic Entry: ocean
    ozone Noun

    form of oxygen that absorbs ultraviolet radiation.

    power plant Noun

    industrial facility for the generation of electric energy.

    precipitation Noun

    all forms in which water falls to Earth from the atmosphere.

    Encyclopedic Entry: precipitation
    public transportation Noun

    methods of movement that are available to all community members for a fee, and which follow a fixed route and schedule: buses, subways, trains and ferries.

    rain Noun

    liquid precipitation.

    Encyclopedic Entry: rain
    recycle Verb

    to clean or process in order to make suitable for reuse.

    reflect Verb

    to rebound or return light from a surface.

    refrigerant Noun

    substance used to keep materials cool.

    respiration Noun

    breathing.

    sea level Noun

    base level for measuring elevations. Sea level is determined by measurements taken over a 19-year cycle.

    Encyclopedic Entry: sea level
    snow Noun

    precipitation made of ice crystals.

    swamp Noun

    land permanently saturated with water and sometimes covered with it.

    Encyclopedic Entry: swamp
    temperate Adjective

    moderate.

    temperature Noun

    degree of hotness or coldness measured by a thermometer with a numerical scale.

    Encyclopedic Entry: temperature
    tropical Adjective

    existing in the tropics, the latitudes between the Tropic of Cancer in the north and the Tropic of Capricorn in the south.

    vapor Noun

    visible liquid suspended in the air, such as fog.

    volcano Noun

    an opening in the Earth's crust, through which lava, ash, and gases erupt, and also the cone built by eruptions.

    Encyclopedic Entry: volcano