Estimating Solar Irradiance Since 850 CE

Abstract

Solar total and spectral irradiance are estimated from 850 to 1610 by regressing cosmogenic irradiance indices against the National Oceanic and Atmospheric Administration Solar Irradiance Climate Data Record after 1610. The new estimates differ from those recommended for use in the Paleoclimate Model Intercomparison Project (PMIP4) in the magnitude of multidecadal irradiance changes, spectral distribution of the changes, and amplitude and phasing of the 11‐year activity cycle. The new estimates suggest that total solar irradiance increased 0.036 ± 0.009% from the Maunder Minimum (1645–1715) to the Medieval Maximum (1100 to 1250), compared with 0.068% from the Maunder Minimum to the Modern Maximum (1950–2009). PMIP4's corresponding increases are 0.026% and 0.055%, respectively. Multidecadal irradiance changes in the new estimates are comparable in magnitude to the PMIP4 recommendations in the ultraviolet spectrum (100–400 nm) but somewhat larger at visible (400–700 nm) and near‐infrared (700–1,000 nm) wavelengths; the new estimates suggest increases from the Maunder Minimum to the Medieval Maximum of 0.17 ± 0.04%, 0.030 ± 0.008%, and 0.036 ± 0.009% in the ultraviolet, visible, and near‐infrared spectral regions, respectively, compared with PMIP4 increases of 0.17%, 0.021%, and 0.016%. The uncertainties are 1σ estimates accruing from the statistical procedures that reconstruct irradiance in the Medieval Maximum relative to the Modern Maximum, not from the specification of Modern Maximum irradiances per se. In the new estimates, solar irradiance cycle amplitudes in the Medieval Maximum are comparable to those in the Modern Maximum, whereas in the PMIP4 reconstruction they are at times almost a factor of 2 larger at some wavelengths and differ also in phase.

Causes of climate change over the historical record

“…Period Only few studies are available that estimate the role of solar forcing alone. Over the last five centuries, reconstructions support only a moderate magnitude of solar forcing (Schurer et al 2014), as do analyses of the instrumental period based on formal attribution (Stott et al 2003, Benestad andSchmidt 2009) and global time series regression analyses (Folland et al 2018, Lean 2018). Analysis also suggests a role of solar forcing in trends ( figure 1(d)), although it is not significant against internal variability in climate models (indicated by the spread of simulations) yet may have slightly influenced trends.…”

Solar Irradiance Variability: Comparisons of Models and Measurements

“…Extension of the NRLTSI2 and NRLSSI2 irradiance estimates from 1610 to 850 CE uses the correlation of average of irradiance variations modeled using two different sunspot number records with cosmogenic isotopes (Lean, 2018). For this reason, irradiance estimates prior to 1882 are provided only as yearly values determined by the relationship of the annually averaged modeled irradiance after 1882 (i.e., the net change of the facular and sunspot influences) with annual sunspot numbers.…”

“…For this reason, irradiance estimates prior to 1882 are provided only as yearly values determined by the relationship of the annually averaged modeled irradiance after 1882 (i.e., the net change of the facular and sunspot influences) with annual sunspot numbers. Extension of the NRLTSI2 and NRLSSI2 irradiance estimates from 1610 to 850 CE uses the correlation of average of irradiance variations modeled using two different sunspot number records with cosmogenic isotopes (Lean, 2018).…”

“…The updated NRLTSI2 and NRLSSI2 models (Coddington et al, 2016;Coddington & Lean, 2015), respectively, specify total and spectral solar irradiance annually since 1610 and daily since 1882 for the operational NOAA Solar Irradiance CDR. For time periods prior to the spacecraft-based record, the models estimate solar irradiance using proxy records of solar activity that span long time periods, such as sunspot numbers and cosmogenic isotopes archived in ice cores and tree rings (Lean, 2018). For the original NRLTSI and NRLSSI models (Lean, 2000;Lean et al, 2005;Lean & Woods, 2010), the observations predated the launch of the SORCE spacecraft.…”

“…At wavelengths not covered by daily instrumental observations (i.e., longer than 400 nm for the original models and longer than 2400 nm for version 2), the NRL models estimate solar irradiance using theoretical estimates of the contrasts of magnetic features. For time periods prior to the spacecraft-based record, the models estimate solar irradiance using proxy records of solar activity that span long time periods, such as sunspot numbers and cosmogenic isotopes archived in ice cores and tree rings (Lean, 2018). The NRL models have been used in many studies of Earth's climate such as the Coupled Model Intercomparison Project (Matthes et al, 2017) and the Paleoclimate Model Intercomparison Project (PMIP) (Schmidt et al, 2011) and in review assessments of Earth's climate by the Intergovernmental Panel on Climate Change (Schimel, 1996;Shine et al, 1990;Solomon et al, 2007).…”