Evidence for long-term brightness changes of solar-type stars

TLDR: In this paper, the magnetic behaviour of a number of solar-type stars over several years has been studied to find indirect evidence that these stars undergo brightness changes of more than the 0.1% observed during the last solar cycle, which calls into question the assumption of a constant Sun in calculations using general circulation models for climate forecasting.

Abstract: CHANGES in the brightness of the Sun may introduce further uncertainties into forecasts of global warming by the greenhouse effect. The Sun is known to vary in brightness, on a timescale of years, by 0.1% in phase with changes in magnetic activity during the solar cycle1–3, and variations of up to 0.4%, also correlated with surface magnetic activity, have been found in stars similar to the Sun4. To delimit the magnitude of solar luminosity variations on a timescale of centuries, we have looked at the magnetic behaviour of a number of solar-type stars over several years. Observed in random phases of their long-term variability, they give a sample of the behaviour of a solar-type star over a long period of time. We find indirect evidence that these stars undergo brightness changes of more than the 0.1% observed during the last solar cycle, a result that calls into question the assumption of a constant Sun in calculations using general circulation models for climate forecasting.