According to the latest IPCC report, AR5, the influence of the sun on our climate since pre-industrial times, in terms of radiative forcing, is very small compared to the effect of greenhouse gases.
According to some more skeptical scientists such a small solar influence is counterintuitive. The Little Ice Age, the period roughly from 1350 to 1850, in which winters on the Northern Hemisphere could be severe and glaciers advanced, coincided with the so-called Maunder Minimum, a period of supposedly low solar activity. In their eyes, the sun therefore still is a serious candidate to also explain a substantial part of the warming since pre-industrial times.
Sunspot records since 1600 suggest there has been a considerable increase in solar activity in the 20th century leading to a Grand Solar Maximum or Modern Maximum. However recently these sunspot records have come under increasing scrutiny and newer reconstructions show a much ‘flatter’ sunspot history. This challenges the idea of a Modern Maximum.
The current solar cycle 24 is the lowest sunspot cycle in 100 years and the third in a trend of diminishing sunspot cycles. Solar physicists expect cycle 25 to be even smaller than Cycle 24 and expect the sun to move into a new minimum, comparable with the Dalton or even the Maunder Minimum. Studying such a minimum with modern instruments could potentially answer a lot of the questions surrounding the influence of the sun on our climate.
We are very pleased that no fewer than five (solar) scientists have agreed to participate in this exciting new Climate Dialogue: Mike Lockwood (UK), Nicola Scafetta (US), Jan-Erik Solheim (NO), José Vaquero (ES) and Ilya Usoskin (FI).
The introduction and guest posts can be read online below. For convenience we also provide pdf’s: