Final answer:
Carbon in the atmosphere arises due to human activities such as the combustion of fossil fuels and deforestation, which contribute significantly to CO₂ emissions.
Step-by-step explanation:
Carbon in the atmosphere is a result of human activity and several factors. These include combustion of fossil fuels (coal, natural gas, and oil) for energy and transportation, which is a major source of CO₂ emissions. Another significant human activity is deforestation, which not only reduces the number of trees that absorb CO₂ but also often involves burning, releasing stored carbon into the atmosphere. Although not options provided in the question, other artificial sources include industrial processes, livestock manure decomposition, and waste from landfills releasing methane, while natural sources involve processes like volcanic eruptions and wildfires.