How have humans contributed to changes in atmospheric CO2 levels?

Humans have significantly contributed to changes in atmospheric CO2 levels primarily through the burning of fossil fuels. When fossil fuels such as coal, oil, and natural gas are burned for energy, they release carbon dioxide into the atmosphere as a byproduct of combustion. This process has dramatically increased the concentration of CO2 in the atmosphere, especially since the Industrial Revolution, leading to climate change and global warming.

While the other factors are also important contributors to increased CO2 levels, burning fossil fuels is a direct and major source of emissions. The combustion process alone accounts for a substantial portion of human-caused CO2 emissions. This action not only raises CO2 levels but also affects other greenhouse gases, compounding the issue of climate change.