The concept of the Sun "coming back on" after an ice age may stem from a misunderstanding. The Sun itself did not go away or cease to exist during an ice age. Instead, an ice age refers to a long period of time characterized by significant cooling of the Earth's climate and the growth of extensive ice sheets and glaciers.
Ice ages are caused by complex interactions between various factors, including variations in Earth's orbit, changes in atmospheric composition, and feedback mechanisms within the climate system. These factors can lead to a decrease in the amount of solar radiation reaching the Earth's surface, resulting in colder temperatures and the formation and expansion of ice.
Ice ages are not sudden events with an abrupt onset or conclusion. They occur over thousands to millions of years and consist of alternating periods of colder temperatures (glacial periods) and warmer interglacial periods. The most recent ice age, called the Pleistocene Ice Age, lasted from about 2.6 million years ago until approximately 11,700 years ago.
The end of an ice age, transitioning into an interglacial period, is typically associated with natural variations in Earth's orbital parameters, known as Milankovitch cycles. These cycles affect the distribution and intensity of solar radiation received by different regions of the Earth, leading to changes in climate. Additionally, other factors, such as volcanic activity and feedback processes within the climate system, can also influence the termination of an ice age.
During the transition from a glacial period to an interglacial period, temperatures gradually rise, causing the ice sheets and glaciers to melt and retreat. This process takes thousands of years. As the ice melts, the land and ecosystems that were once covered by ice become exposed again, allowing for the reestablishment of plant and animal life.
It is important to clarify that the Sun did not disappear or undergo any significant change during or after an ice age. Rather, ice ages are a result of complex climatic variations on Earth caused by a combination of factors, and the transition out of an ice age involves gradual climate changes over a long period of time.