The past few decades were the warmest during the past millennium (IPCC 2001; Osborn and Briffa 2006, and references therein) owing to greenhouse gas-induced warming. The temperature rise during the first half of the last century, however, is clearly linked to increased solar activity (Lockwood et al. 1999). Reconstruction of the solar variability reveals that, at present, the Sun is in a very active phase, but shows no clear indication of a trend since 1980 when the satellite-based measurements of the total solar irradiance (TSI) began. Based on paleorecords, and considering the fact that amplification mechanisms for changing solar activity are not well understood - and therefore cannot yet be sufficiently quantified in climate models - we conclude that the solar forcing of climate change may be more important than has been suggested by the Intergovernmental Panel on Climate Change (IPCC 2001). If the Little Ice Age and the subsequent warming were mainly driven by changes in solar activity this component of natural forcing plays an important role in estimating the future climate warming induced by greenhouse gases due to human activities. A future major decline of solar activity as predicted by de Jager (2005) may bring further progress in our understanding of present and future climate change.

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