Which of the following human activities contributes most significantly to increased carbon dioxide levels?

Fossil fuel combustion is the activity that most significantly contributes to increased carbon dioxide levels in the atmosphere. When fossil fuels such as coal, oil, and natural gas are burned for energy, they release substantial amounts of carbon dioxide as a byproduct. This process is central to electricity generation, transportation, and industrial processes, making it a primary source of anthropogenic carbon emissions.

The vast scale of fossil fuel consumption globally means that its impact on carbon dioxide levels is profound, driving climate change and influencing global temperatures. This activity not only contributes directly to greenhouse gas emissions but also affects the carbon cycle by altering the balance of carbon stored in natural reservoirs.

In contrast, while agricultural practices and deforestation do contribute to greenhouse gas emissions, including carbon dioxide and methane, their overall contribution is lower compared to fossil fuel combustion. Recycling also plays a role in reducing emissions by minimizing waste and energy use but does not emit significant carbon dioxide itself. Therefore, the predominant driver of increased atmospheric carbon dioxide remains the burning of fossil fuels.