Abstract
A set of global climate model simulations for the last thousand years developed by the Max Planck Institute is compared with paleoclimate proxy data and instrumental data, focusing on surface temperatures for land areas between 30° and 75°N. The proxy data are obtained from six previously published Northern Hemispheric-scale temperature reconstructions, here re-calibrated for consistency, which are compared with the simulations utilizing a newly developed statistical framework for ranking several competing simulations by means of their statistical distance against past climate variations. The climate model simulations are driven by either “low” or “high” solar forcing amplitudes (0.1 and 0.25 % smaller total solar irradiance in the Maunder Minimum period compared to the present) in addition to several other known climate forcings of importance. Our results indicate that the high solar forcing amplitude results in a poorer match with the hemispheric-scale temperature reconstructions and lends stronger statistical support for the low-amplitude solar forcing. However, results are likely conditional upon the sensitivity of the climate model used and strongly dependent on the choice of temperature reconstruction, hence a greater consensus is needed regarding the reconstruction of past temperatures as this currently provides a great source of uncertainty.
Highlights
Solar irradiance can impact upon the global climate through its variations (Gray et al 2010)
A set of global climate model simulations for the last thousand years developed by the Max Planck Institute is compared with paleoclimate proxy data and instrumental data, focusing on surface temperatures for land areas between 30° and 75°N
The climate model simulations are driven by either ‘‘low’’ or ‘‘high’’ solar forcing amplitudes (0.1 and 0.25 % smaller total solar irradiance in the Maunder Minimum period compared to the present) in addition to several other known climate forcings of importance
Summary
Solar irradiance can impact upon the global climate through its variations (Gray et al 2010). TSI has been directly measured using instruments mounted on satellites as of the mid-1970s, before this period it must be reconstructed based on proxy indices of solar irradiance found to correlate with TSI variations during the instrumental period Recent estimates of these solar activity indices have generally been based on sunspot numbers and/or solar magnetic flux changes (derived from geomagnetic information or cosmogenic isotopes). The magnitude of TSI variations is often portrayed as the hypothesized reduction, compared to present values, during the Maunder Minimum period (AD 1645–1715; characterized by low solar activity Eddy (1976) This reduction is widely regarded, of present, as being in the range 0.04–0.1 %, as adopted by the Paleoclimate Model Intercomparison Project Phase III (PMIP3) (Schmidt et al 2011). This, in turn, would correspond in magnitude to about 40 % of the radiative forcing from increased greenhouse-gas concentrations over the twentieth century (Lockwood 2011)
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