Final answer:
Climate changes over millennia are driven mainly by Milankovitch cycles impacting Earth's orbit and axis, fluctuations in solar activity, and volcanic eruptions, all altering the planet's long-term climate patterns.
Step-by-step explanation:
Climate changes throughout thousands to hundreds of thousands of years are primarily driven by Milankovitch cycles, variations in solar activity, and volcanic eruptions. The Milankovitch cycles, which include changes in Earth's orbit and axis, have the most significant impact at these time scales. These orbital patterns include changes in eccentricity, obliquity, and precession, which alter Earth's distance from the sun and the distribution of sunlight on Earth, thus influencing long-term climate patterns.
Volcanic eruptions can cause short-term cooling effects by releasing particulate matter and sulfur dioxide into the atmosphere, blocking sunlight. However, these are temporary compared to the lengthy Milankovitch cycles. Solar variations, such as changes in solar irradiance, also affect the climate but have been relatively consistent since the mid-20th century.
The combined effect of these natural phenomena has been responsible for the swings in global climate, such as the transition between ice ages and warmer interglacial periods. It’s important to note that while these processes can explain past climate change, recent warming trends are more likely related to human activities.