Final answer:
The main man-made source of carbon dioxide is deforestation, which releases stored carbon when trees are cut down and burned or left to decompose. Another major source is the burning of fossil fuels. These activities contribute to the greenhouse effect by increasing atmospheric CO2 levels, trapping more infrared heat, and leading to global warming.
Step-by-step explanation:
Among the options provided, the main man-made source of carbon dioxide (CO2) is deforestation. This is because when forests are cleared, not only are the trees that absorb CO2 removed, but the stored carbon is often released into the atmosphere through burning or decomposition of the felled trees. In addition to this, burning fossil fuels such as coal, oil, and natural gas is another significant contributor to human-related CO2 emissions. These activities sharply increase the concentration of CO2 in the atmosphere, contributing to the greenhouse effect and global warming.
The greenhouse effect is a natural process that warms the Earth's surface. When the sun's energy reaches the Earth's atmosphere, some of it is reflected back to space and the rest is absorbed and re-radiated as infrared heat. Greenhouse gases like CO2 absorb this heat, trapping it in the atmosphere, which makes the Earth warmer. This effect is being strengthened by human activities that release more CO2, trapping more heat and thus contributing to global warming.