Final answer:
The decrease in solar irradiance during low sunspot activity may be greater than previously thought. Alternative possibilities such as volcanic activity and changes in surface reflectivity can affect global temperatures. Variations in solar activity can also impact the atmosphere, potentially influencing weather patterns.
Step-by-step explanation:
The decrease in solar irradiance during low sunspot activity may be greater than previously thought. While there is no satisfactory model that explains how a reduction in solar activity causes cooler temperatures on Earth, alternative possibilities include the role of volcanic activity and changes in surface reflectivity. Observations of volcanic eruptions and the reduction of sunlight reaching Earth's surface due to aerosols have resulted in measurable decreases in global temperatures. Additionally, variations in solar activity can affect the chemistry and temperature structure of the upper atmosphere, potentially impacting weather and climate patterns.