A network of interdisciplinary scholars studying past climate change
The article D.M. Anderson et al., “Global Warming in an Independent Record of the Past 130 Years,” published here in Geophysical Research Letters, uses an index of 173 temperature-sensitive proxies to reconstruct global temperatures going back to 1880, and a smaller index of 67 proxies to extend the record back to 1730. The results strongly mirror those of the instrumental record, with clear indications of accelerating warming in the 20th century. The study notes that “The upward trend appears to begin in the early 19th century but the year-to-year variability is large and the 1730-1929 trend is small.”
Of course, for climate historians the study also serves as a nice confirmation of the validity of proxies in historical climate reconstruction. The broad Paleo Index used in the study actually shows much stronger correlation with the instrumental record than single, local proxies tend to do.