Final answer:
The cause of regular carbon dioxide fluctuations in the atmosphere is natural processes such as respiration and volcanic eruptions, as well as the weathering of rocks. The burning of fossil fuels by human activities has significantly increased carbon dioxide levels, leading to climate change.
Step-by-step explanation:
The cause of regular carbon dioxide fluctuations in the atmosphere is primarily due to natural processes such as respiration, volcanic eruptions, and the weathering of rocks. These processes release carbon dioxide into the atmosphere, leading to cyclical fluctuations. However, the burning of fossil fuels by human activities has dramatically increased the levels of carbon dioxide in the atmosphere, contributing to the current climate change and increasing biodiversity impacts.