Final answer:
Climate change over millennia is primarily driven by natural factors such as Milankovitch cycles, volcanic eruptions, and solar activity, while in recent decades, human activities, particularly the combustion of fossil fuels, have become the primary cause, leading to increased greenhouse effect and global warming.
Step-by-step explanation:
Mechanisms that Drive Climate Change
The mechanisms behind climate change vary depending on the time scale being considered. Over thousands to hundreds of thousands of years, climate change is predominantly driven by Milankovitch cycles, which are long-term changes in the Earth's orbital patterns, including its eccentricity, obliquity, and precession. These cycles influence the amount and distribution of solar energy received by the Earth. Additionally, volcanic eruptions can create aerosols and dust that reflect sunlight, leading to temporary cooling, while variations in solar activity can also induce climate changes.
In recent decades, the climate change observed cannot be solely attributed to these natural factors. The rapid increase in global temperatures and the sustained growth in atmospheric carbon dioxide levels are closely linked to human activities, especially the burning of fossil fuels, which intensifies the greenhouse effect. This human-induced alteration of the carbon cycle is the main driver of current climate change.