Author: V. Ramaswamy, NOAA/ Geophysical Fluid Dynamics Laboratory, Princeton University
Variations and secular changes in the Sun's irradiance output constitute an important forcing agent capable of perturbing the Earth's radiative energy balance. Observations of the irradiance variations over the past two decades have revealed a wealth of quantitative information about the nature of solar variations on this timescale, while attempts have been made to reconstruct the changes in irradiance further back in time.
We will discuss the current state of knowledge of this forcing in the context of the Earth's climate change over the past century. We will also discuss uncertainties in this knowledge and its implications, particularly when viewed against the other known forcing agents.
Solar irradiance affects both the tropospheric climate and stratospheric thermal balance. The manner in which the solar-induced changes compare and contrast against the climate impacts due to other forcings will be reviewed. The effect of the solar irradiance variations upon stratospheric temperature changes will also be discussed.