Which variable is crucial in studying climate change?

The historical record of solar output is crucial in studying climate change because it provides insights into how variations in solar radiation can influence the Earth's climate over long periods. Solar output affects the amount of energy the Earth receives, which directly impacts temperature, weather patterns, and, consequently, climate over time. Understanding changes in solar output helps scientists differentiate between natural climate variability and changes driven by human activities, such as greenhouse gas emissions.

In contrast, while yearly rainfall amounts are important for understanding specific weather patterns and regional climates, they do not provide the broader context needed for understanding long-term climate changes. The distance of Earth from the Sun does influence climate, but since this distance remains relatively constant over human timescales, it is less relevant for current climate change studies. Migration patterns of animals can indicate changes in climate, such as shifting habitats or breeding seasons, but they are more of a consequence of climate change rather than a fundamental driver of it. Therefore, the historical record of solar output offers the foundational context needed for interpreting climate shifts through the lens of natural variability.