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A New History of Total Solar Irradiance Since AD 1700
Krivova, N.A., Balmaceda, L. and Solanki, S.K. 2007. Reconstruction of solar total irradiance since 1700 from the surface magnetic flux. Astronomy & Astrophysics 467: 335-346.

Krivova et al. note there is "strong interest" in the subject of long-term variations of total solar irradiance (TSI) "due to its potential influence on global climate," and that "only a reconstruction of solar irradiance for the pre-satellite period with the help of models can aid in gaining further insight into the nature of this influence," which is what they set about to do in their paper.

What was done
The three scientists from the Max-Planck-Institut fur Sonnensystemforschung developed a history of TSI "from the end of the Maunder minimum [about AD 1700] to the present based on variations of the surface distribution of the solar magnetic field," which was "calculated from the historical record of the sunspot number using a simple but consistent physical model," i.e., that of Solanki et al. (2000, 2002).

What was learned
Krivova et al. report that their model "successfully reproduces three independent data sets: total solar irradiance measurements available since 1978, total photospheric magnetic flux since 1974 and the open magnetic flux since 1868," which was "empirically reconstructed using the geomagnetic aa-index." Based on this model, they reconstruct an increase in TSI since the Maunder minimum somewhere in the range of 0.9-1.5 Wm-2, which encompasses the results of several independent reconstructions that have been derived over the past few years. In the final sentence of their paper, however, they also note that "all the values we obtain are significantly below the ΔTSI values deduced from stellar data and used in older TSI reconstructions," the results of which range from 2 to 16 Wm-2.

What it means
Although there is still significant uncertainty about the true magnitude of the TSI change experienced since the end of the Maunder minimum, the wide range of possible values suggests that long-term TSI variability cannot be rejected out-of-hand as a possible cause of the majority of the global warming that has fueled earth's transition from the chilling depths of the Little Ice Age to the much milder weather of the Current Warm Period.

Solanki, S.K., Schussler, M. and Fligge, M. 2000. Evolution of the sun's large-scale magnetic field since the Maunder minimum. Nature 408: 445-447.

Solanki, S.K., Schussler, M. and Fligge, M. 2002. Secular variation of the Sun's magnetic flux. Astronomy & Astrophysics 383: 706-712.

Reviewed 3 October 2007