This is interesting. This recent paper published in the journal Astronomy & Astrophysics here has done a reconstruction of TSI using Beryllium 10 isotope records combined with sunspot records. The paper suggests that the Total Solar Irradiance (TSI) has increased since the end of the Little Ice Age (around 1850) by up to 6 x more than cited by the IPCC.
Here is how they did it:
For the reconstruction to the past this amplitude is scaled with proxies for solar activity. Two proxies are available for the reconstruction: Group sunspot number, which is available from the present to 1610 AD, and the solar modulation potential extending back to circa 7300 BC. The latter is a measure of the heliospheric shielding from cosmic rays derived from the analysis of cosmogenic isotope abundances in tree rings or ice
cores, and is available with a time resolution of 2-3 solar cycles (Steinhilber et al. 2008). Although sunspot number dropped to zero for a long time during the Maunder minimum, the solar cycle was uninterrupted (Beer et al. 1998; Usoskin et al. 2001) and the modulation potential did not fall to zero. Hence, a reconstruction based solely on sunspot number may underestimate the solar activity during theMaunderminimum. Therefore in our reconstruction we used the solar modulation potential to calculate the long-term variations and sunspot number to superpose them with the 11-year cycle variations (see the Online Section 6.2).
The modulation potential used in the calculations is based on the composite of data determined from the cosmogenic isotope records of 10Be and neutronmonitor. 10Be data are available up to about 1970 (McCracken et al. 2004) and neutron monitor data, which are used to calculate the current solar modulation potential, are available since the 1950s.
A. I. Shapiro, W. Schmutz1, E. Rozanov, M. Schoell, M. Haberreiter1, A. V. Shapiro and S. Nyeki
1 Physikalisch-Meteorologishes Observatorium Davos, World Radiation Center, 7260 Davos Dorf, Switzerland
2 Institute for Atmospheric and Climate science ETH, Zurich, Switzerland
3 Institute for Astronomy ETH, Zurich, Switzerland
Context. The variable Sun is the most likely candidate for the natural forcing of past climate changes on time scales of 50 to 1000 years. Evidence for this understanding is that the terrestrial climate correlates positively with the solar activity. During the past 10 000 years, the Sun has experienced the substantial variations in activity and there have been numerous attempts to reconstruct solar irradiance. While there is general agreement on how solar forcing varied during the last several hundred years – all reconstructions are proportional to the solar activity – there is scientific controversy on the magnitude of solar forcing. Aims. We present a reconstruction of the total and spectral solar irradiance covering 130 nm–10 μm from 1610 to the present with an annual resolution and for the Holocene with a 22-year resolution. Methods. We assume that the minimum state of the quiet Sun in time corresponds to the observed quietest area on the present Sun. Then we use available long-term proxies of the solar activity, which are 10Be isotope concentrations in ice cores and 22-year smoothed neutron monitor data, to interpolate between the present quiet Sun and the minimum state of the quiet Sun. This determines the long-term trend in the solar variability, which is then superposed with the 11-year activity cycle calculated from the sunspot number. The time-dependent solar spectral irradiance from about 7000 BC to the present is then derived using a state-of-the-art radiation code.
We present a new technique to reconstruct total and spectral solar irradiance over the Holocene. We obtained a large historical solar forcing between the Maunder minimum and the present, as well as a significant increase in solar irradiance in the first half of the twentieth-century. Our value of the historical solar forcing is remarkably larger than other estimations published in the recent literature.
We note that our conclusions can not be tested on the basis of the last 30 years of solar observations because, according to the proxy data, the Sun was in a maximumplato state in its longterm evolution.All recently published reconstructions agree well during the satellite observational period and diverge only in the past. This implies that observational data do not allow to select and favor one of the proposed reconstructions. Therefore, until new evidence become available we are in a situation that different approaches and hypothesis yield different solar forcing values. Our result allows the climate community to evaluate the full range of present uncertainty in solar forcing.
The full dataset of the solar spectral irradiance back to 7000
BC is available upon request.