The "biggest thorn in the side" paper RWG found, http://www.jpands.org/vol12no3/robinson600.pdf also contains this large error: "Between 1900 and 2000, on absolute scales of solar irradiance and degrees Kelvin, solar activity increased 0.19%, while a [USA-average] 0.5C temperature change is 0.21%." The problem is, a 1.0019 factor increase in solar power should lead to an earth temperature increase (same earth) of that factor to the power 1/4, namely 1.000475 NOT 1.0021. So in short: thank you Robinson et al, for disproving your own idea solar changes are the main cause of the warming. (Idiot.) ------ Oddly enough, just today this new paper hit the hype-o-matic: http://www.ncas.ac.uk/index.php/en/climate-science-highlights/978-small-infl... (see also http://www.research.ed.ac.uk/portal/files/8542848/PDF_Schurer.et.al2013INPRE...) which studies this very question using various historical and geo/bio data (e.g. tree rings, volcanic eruptions). I have no idea how much to trust it, but it claims its conclusions are that 1. variations in solar output and explosive volcanism were the main drivers of climate change from 1400-1900 2. we are also able to detect a significant contribution from greenhouse gas variations to the cold conditions during 1600-1800 3. after 1900 the main driver was human generated greenhouse gases.