Glossary Hydroelectric

albedo A measure of the amount of sunlight an object reflects.

atoll A coral island encircling a lagoon.

carbon dioxide (CO2) A greenhouse gas chemically composed of carbon and oxygen. Carbon dioxide is produced by the burning of fossil fuels such as oil and coal. It is also exhaled by human beings and inhaled by plants. Burning plants also releases carbon dioxide.

continental climates Climates that are relatively cold in winter and hot in summer; usually found at the interiors of continents.

El NiƱo A periodic oceanic warming, which can have major effects on weather.

feedback loop A process in which one condition creates other conditions that reinforce the first.

glacier A mass of ice that year-round is located on and moves over land.

global warming The increase in the average temperature of the earth's surface and oceans. Global warming has been occurring since the mid-twentieth century, and it is expected to continue because of the greenhouse effect.

greenhouse effect The heating of the surface of the earth due to the presence of gases that trap energy from the sun.

greenhouse gases Substances that contribute to the greenhouse effect and global warming. Carbon dioxide, methane, and water vapor are all greenhouse gases.

groundwater Water located underneath the ground, either in porous soil or in spaces in rock.

Hurricane Katrina The 2005 storm that devastated the city of New Orleans.

hydroelectric power Electrical power generated by dams.

hydrologic cycle The circulation of water from the earth's surface as a solid or liquid to the air as water vapor and back to the earth as precipitation.

hydropower Power derived from the motion of water.

ice sheet A mass of glacial ice more than 20,000 square miles (50,000 sq. km) in area.

ice shelf A floating platform of ice that forms at the junction of a glacier and a coastline.

Intergovernmental Panel on Climate Change (IPCC) A scientific body established by the United Nations to evaluate the risk of climate change caused by human activity.

jet stream Fast flowing, narrow air currents in the atmosphere.

mangroves Trees and shrubs that grow in salt-water habitats.

maritime climates Climates that are relatively warm in winter and mild in summer; usually located near the ocean.

methane A greenhouse gas about 20 times more potent than carbon dioxide. Methane gas is produced when organic matter decays in the absence of oxygen. It also exists below the earth's surface and is produced in the intestines of livestock, such as cows, which release it into the atmosphere through flatulence.

monsoons Seasonal winds, which often have a profound effect on seasonal precipitation.

moulin A narrow, tubular chute, hole, or crevasse through which water enters a glacier from its surface.

North Atlantic Current An important ocean current in the Atlantic that moves warm surface waters from the equator north toward the Arctic, then sinks down and pulls cold water back toward the equator.

snowpack Naturally formed compressed snow. It is especially common in mountainous regions, and it often melts in springtime.

specific heat A measure of the amount of energy needed to increase the temperature of a substance by a set amount.

sublimation The process whereby snow or ice turns directly into water vapor.

thermal expansion The increase in volume in matter caused by an increase in temperature. Thermal expansion of ocean water as a result of global warming is believed to be one of the major short-term causes of sea-level rise.

tidal power The conversion of tidal energy into useful forms of power.

transpiration The release of water from plants.

wave power The conversion of wave energy into useful forms of power.

wetlands An area of land whose soil is saturated with moisture, either permanently or seasonally.

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