Answer: Carbon dioxide is the primary greenhouse gas emitted through human activities. In 2019, accounted for about 80 percent of all U.S. greenhouse gas emissions from human activities. Carbon dioxide is naturally present in the atmosphere as part of the Earth's carbon cycle (the natural circulation of carbon among the atmosphere, oceans, soil, plants, and animals. Human activities are altering the carbon cycle–both by adding more to the atmosphere, and by influencing the ability of natural sinks, like forests and soils, to remove and store from the atmosphere. While emissions come from a variety of natural sources, human-related emissions are responsible for the increase
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