Final answer:
Human activities such as the burning of fossil fuels, deforestation, cement production, and livestock agriculture significantly increase CO2 levels in the atmosphere, alongside methane emissions from organic waste and natural gas production.
Step-by-step explanation:
Human activities contribute to the rise in atmospheric CO2 levels in various ways. The most prominent among these is the combustion of fossil fuels, which includes coal, natural gas, and oil for energy and transportation. Another significant source is deforestation, which not only releases CO2 through the burning of trees but also reduces the number of plants available to absorb CO2 during photosynthesis. Additionally, the production and use of cement contribute to CO2 emissions. Cement manufacture involves the calcination of limestone (calcium carbonate), which releases CO2.
Also, animal agriculture is responsible for CO2 release, mainly through enteric fermentation in cattle and other farm animals and from the decomposition of organic waste including livestock manure. Methane, another potent greenhouse gas, is released in significant quantities due to human activities such as organic waste decomposition in landfills, livestock agriculture, and the production of natural gas. This is a concern because methane has a much higher global warming potential per molecule compared to CO2.