I just saw an interesting new paper by Lean and Rind in Geophysical Research Letters . These authors performed a multiple regression analysis to determine the influence of natural (solar activity, volcanoes, ENSO) and anthropogenic (greenhouse gases plus aerosols) factors on the temperature record of the past 100+ years. Looks like a good piece of work.
The "solar activity" and "natural cycles" skeptics will not like the conclusions, though. None of the natural factors comes close to explain the overall warming trend. A citation from the paper:
"None of the natural processes can account for the overall warming trend in global surface temperatures. In the 100 years from 1905 to 2005, the temperature trends produced by all three natural influences are at least an order of magnitude smaller than the observed surface temperature trend reported by IPCC . According to this analysis, solar forcing contributed negligible long-term warming in the past 25 years and 10% of the warming in the past 100years, not 69% as claimed by Scafetta and West ..."