Final answer:
The solar irradiance has varied since 1750. According to a study by Kopp and Lean (2011), there is evidence of a new, lower value of total solar irradiance.
Step-by-step explanation:
The solar irradiance has varied since 1750. According to a study by Kopp and Lean (2011), there is evidence of a new, lower value of total solar irradiance. Solar irradiance refers to the power per unit area received from the Sun at a given distance. It is measured in watts per square meter (W/m²). The variations in solar irradiance can have an impact on climate and weather patterns on Earth.