From Global Warming Art
"An understanding of climate history prior to industrialization is crucial to understanding the nature of the 20th century warming and to predicting the climate change in the near future. This study integrates the complementary information preserved in the global database of borehole temperatures, the 20th century meteorological record, and an annually resolved multi proxy model for a more complete picture of the Northern Hemisphere temperature change over the past five centuries. The integrated reconstruction shows that the 20th century warming is a continuation to a long-term warming started before the onset of industrialization. However, the warming appears to have been accelerated towards the present day. Analysis of the reconstructed temperature and radiative forcing series offers an independent estimate of the transient climate-forcing response rate of 0.4–0.7 K per Wm−2 and predicts a temperature increase of 1.0–1.7 K in 50 years."
The following pages on Global Warming Art refer to this reference: