Glossary

acid rain: rain or snow with higher than normal levels of acidic compounds, such as sulfuric acid and nitric acid. The compounds come from air pollution, mix with water vapor inside clouds, and fall as precipitation. When it reaches lakes, rivers, and soil, acid rain can kill fish and other wildlife. Acid can also eat away at the surface of buildings, bridges, and other structures.

aerosol: a mixture of extremely small particles or droplets suspended inside gas. In the air, aerosols can take the form of smoke, mist, fog, or clouds. Some particles in aerosols, such as volcanic ash and pollen, enter the atmosphere naturally. Other particles enter the air when people burn fossil fuels. High in the atmosphere, aerosols reflect sunlight back into space. So some climate scientists propose inserting aerosols into the stratosphere to fight global warming. The aerosols would deflect sunlight, leading to lower temperatures on Earth.

albedo: a measure of how much of the sun’s radiation is being reflected back into space. The measurement can range from a 0, or no reflection, to 1, or 100 percent reflection. Different surfaces on Earth, such as clouds, ice caps, and oceans, have different albedos. The albedo average for the planet as a whole is about 0.31, so Earth reflects about one-third of the radiation it receives from the sun.

atmosphere: the layer of gases surrounding Earth or another planet. Some of the gases, such as carbon dioxide, methane, and water vapor, trap heat near the planet. As people have burned more and more fossil fuels, atmospheric carbon dioxide levels have risen, trapping more heat and leading to climate change on Earth.

biochar: charcoal produced by the burning of plant matter for fuel. Some environmentalists propose placing large amounts of biochar on farm fields, where it will absorb rainwater, keep the soil moist, and help crops grow. Then the carbon inside biochar will simply remain there, not moving into the atmosphere to increase carbon levels.

biomass: organic matter that can be burned as fuel, such as leaves, sticks, grass, wood chips, and bark. Because plants practice photosynthesis and absorb carbon dioxide, biomass contains carbon. When biomass is burned, it releases this carbon back into the atmosphere. The amount of carbon taken from the atmosphere during photosynthesis and released into the atmosphere during burning cancels itself out. So we say that biomass is carbon neutral.

carbon cycle: the series of natural and industrial processes by which carbon travels through the environment. In the natural carbon cycle, carbon moves through the air, rocks, soil, volcanoes, clouds, rain, the oceans, and the bodies of plants and animals in an endless loop. In the natural cycle, atmospheric levels of carbon remain steady. However, by extracting fossil fuels from deep underground and burning them, people have increased atmospheric carbon levels.

carbon dioxide: a colorless and odorless greenhouse gas vital to life on Earth. All green plants use carbon dioxide to make food. Animals produce carbon dioxide when they convert food into energy. Carbon dioxide is a greenhouse gas—it traps the sun’s heat near Earth. Excess carbon dioxide in the atmosphere, caused by the burning of fossil fuels, has led to higher temperatures on Earth.

carbon neutral: having net-zero carbon emissions by taking out of the atmosphere the same amount of carbon that is released into the atmosphere

carbon sink: an area that absorbs large amounts of carbon dioxide from the atmosphere. Natural carbon sinks include forests, oceans, soil, and rocks.

climate change: in the modern era, the warming of Earth’s atmosphere caused by the burning of fossil fuels. The release of heat-trapping carbon dioxide into the atmosphere has altered Earth’s climate and led to more extreme weather, including droughts, floods, and ferocious storms.

cloud brightening: a proposed geoengineering technique that involves pumping seawater into low-level clouds. The salt in the seawater would increase the surface area of the water droplets in the clouds. With more surface area, the clouds would become more reflective and send more of the sun’s light back into space. The result would be lower temperatures on Earth.

cloud seeding: adding particles or gases to a cloud to cause it to precipitate, or make rain or snow. Farmers sometimes use cloud seeding to bring rain to a specific area. Nations have also used cloud seeding during warfare to flood enemy lands.

ecosystem: an ecological community consisting of interdependent biological and physical entities. The biological members of an ecosystem are the plants and animals that live there. The physical members are elements such as air, soil, water, and weather. Members of an ecosystem interact with and depend on one another. For instance, certain plants in an ecosystem might serve as food for certain animals.

erosion: natural processes such as water flow and wind that carry soil and rock from one location on Earth to another. Erosion can damage an ecosystem. For instance, strong winds might carry off rich topsoil from farm fields, leaving them dry and dusty. Without a layer of topsoil, fields cannot absorb rainwater needed to nourish plants.

evaporation: the process by which liquid water changes into water vapor, or water in gas form. Evaporation occurs when water is heated. Rising temperatures on Earth, caused by heat-trapping gases in the atmosphere, are leading to increased evaporation.

fossil fuels: fuels formed inside Earth from the remains of ancient plants and animals. Coal, petroleum, and natural gas are examples of fossil fuels. They contain carbon from the long-dead bodies of the plants and animals from which they formed. When people burn fossil fuels, that carbon enters the atmosphere.

geoengineering: the deliberate large-scale manipulation of Earth’s climate. Some scientists propose using geoengineering to halt or reverse human-made climate change and global warming. Proposed geoengineering techniques include cloud brightening, carbon capture and sequestration, and deflecting sunlight by using mirrors in outer space.

greenhouse gas: a gas that traps heat in Earth’s atmosphere. Examples include carbon dioxide and methane. Human activities such as the burning of fossil fuels have released extra greenhouse gases into the atmosphere, leading to global climate change.

limestone: a rock composed mainly of calcium carbonate. Many marine animals, including corals, oysters, and clams, use calcium carbonate from the water to build their shells and bones. After they die, over millions of years, the calcium carbonate in their bodies turns into limestone.

meteorologist: a scientist who studies weather and the atmosphere

ozone layer: a region of Earth’s stratosphere that holds a thick band of ozone. This layer of gas absorbs harmful radiation from the sun. By absorbing this radiation, the ozone layer protects life on Earth.

particulates: microscopic particles and droplets of liquid suspended in Earth’s atmosphere. Particulates can combine with moisture in the air to form smog, a type of air pollution.

photosynthesis: the process by which plants, algae, and some other organisms use sunlight, carbon dioxide, and water to make food. Large areas covered with plants, such as forests, absorb vast amounts of carbon from the air to use in photosynthesis. When people cut down forests, fewer plants are left to absorb carbon.

phytoplankton: plantlike organisms that live at or near the surface of oceans, lakes, and other bodies of water. Phytoplankton are important to the carbon cycle in two ways. First, they practice photosynthesis—they absorb carbon dioxide from the atmosphere to make food. Phytoplankton also use calcium carbonate from the water to build their protective shells. After they die, the carbon in their bodies turns into limestone. Carbon stored in limestone might remain underground or underwater for millions of years.

reforestation: planting new trees in areas where forests have been destroyed or in places where trees haven’t grown before. Reforestation might help fight climate change because trees in forests absorb so much carbon dioxide to use in photosynthesis.

renewable energy: fuel that replaces itself naturally or that never runs out. Examples include biomass, since people can grow new plants to replace those burned for fuel. Another example is solar power, since the sun will keep shining for billions of years.