  How the solar electromagnetic energy entering the Earth's atmosphere varied
since pre-industrial times is an important consideration in the climate change
debate. Detrimental to this debate, estimates of the change in total solar
irradiance (TSI) since the Maunder minimum, an extended period of weak solar
activity preceding the industrial revolution, differ markedly, ranging from a
drop of 0.75 Wm-2 to a rise of 6.3 Wm-2. Consequently, the exact contribution
by solar forcing to the rise in global temperatures over the past centuries
remains inconclusive. Adopting a novel approach based on state-of-the-art solar
imagery and numerical simulations, we establish the TSI level of the Sun when
it is in its least-active state to be 2.0 +/- 0.7 Wm-2 below the 2019 level.
This means TSI could not have risen since the Maunder minimum by more than this
amount, thus restricting the possible role of solar forcing in global warming.
