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:
- Drive less. Use public transportation, carpool, walk, or ride a bike.
- Fly less. Airplanes produce huge amounts of greenhouse gas emissions.
- Reduce, reuse, and recycle.
- Plant a tree. Trees absorb carbon dioxide, keeping it out of the atmosphere.
- Use less electricity.
- 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.
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.
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.
edge of land along the sea or other large body of water.
Encyclopedic Entry: coast crop Noun
Encyclopedic Entry: crop electricity Noun
set of physical phenomena associated with the presence and flow of electric charge.
conditions that surround and influence an organism or community.
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).
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.
water that is not salty.
state of matter with no fixed shape that will fill any container uniformly. Gas molecules are in constant, random motion.
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.
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.
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.
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.
freshwater that comes from melting snow or ice.
chemical compound that is the basic ingredient of natural gas.
having to do with very small organisms.
process of extracting ore from the Earth.
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.
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.
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.
Encyclopedic Entry: rain recycle Verb
to clean or process in order to make suitable for reuse.
to rebound or return light from a surface.
substance used to keep materials cool.
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.
land permanently saturated with water and sometimes covered with it.
Encyclopedic Entry: swamp temperate Adjective
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.
visible liquid suspended in the air, such as fog.
an opening in the Earth's crust, through which lava, ash, and gases erupt, and also the cone built by eruptions.
Encyclopedic Entry: volcano