In grade 6, students learned that Earth's climate system consists of the hydrosphere (water), the atmosphere (air), the geosphere (solid part of Earth), and the biosphere (the living components).  

Many factors can influence different components of the climate system, including greenhouse gases. Greenhouse gases can be released and absorbed in various ways.  Carbon dioxide enters the atmosphere through burning fossil fuels (coal, natural gas, and oil), solid waste, trees, and other biological materials and also as a result of certain chemical reactions (e.g., manufacture of cement). Carbon dioxide is removed from the atmosphere (or sequestered) when it is absorbed by plants as part of the biological carbon cycle. Methane is emitted during the production and transport of coal, natural gas, and oil. Methane emissions also result from livestock and other agricultural practices, land use activities, and the decay of organic waste in municipal solid waste landfills. Nitrous oxide is emitted during agricultural, land use, and industrial activities; combustion of fossil fuels and solid waste; and treatment of wastewater.  Fluorinated gases (hydrofluorocarbons, perfluorocarbons, sulfur hexafluoride, and nitrogen trifluoride) are synthetic, powerful greenhouse gases that are emitted from a variety of industrial processes. Fluorinated gases are sometimes used as substitutes for stratospheric ozone-depleting substances (e.g., chlorofluorocarbons, hydrochlorofluorocarbons, and halons). These gases are typically emitted in smaller quantities, but because they are potent greenhouse gases, they are sometimes referred to as High Global Warming Potential gases.